MPG Quest
MPG Quest
Car: 1982 300SD
I am looking for ideas on how to get the highest MPG's.
My rough idea starts with increasing hp/tq by about 20%, decrease final drive ratio, lower ride height for decreased wind resistance, thin tires (currently 205's) at high pressure (35-40 psi), blocking off lower bumper, shedding some weight.
Target: 700+ miles per tank (35mpg?)
How would you go about this?
Ron Burgundy
1982 300SD - 310,XXX - Orient Red
Hello Everyone,
Car: 1982 300SD
I am looking for ideas on how to get the highest MPG's.
My rough idea starts with increasing hp/tq by about 20%, decrease final drive ratio, lower ride height for decreased wind resistance, thin tires (currently 205's) at high pressure (35-40 psi), blocking off lower bumper, shedding some weight.
Target: 700+ miles per tank (35mpg?)
How would you go about this?
Ron Burgundy
1982 300SD - 310,XXX - Orient Red
(04-29-2010, 04:38 PM)arceo_1 Target: 700+ miles per tank (35mpg?)
Not possible with the slushbox. You'll be lucky to touch 28mpg on straight highway/24 city.
ForcedInduction
04-29-2010, 05:21 PM
#2
(04-29-2010, 04:38 PM)arceo_1 Target: 700+ miles per tank (35mpg?)
Not possible with the slushbox. You'll be lucky to touch 28mpg on straight highway/24 city.
How about a 2.24 or 2.47 rear end?
If 70 mph = 3000 rpm, dumb math tells me that a 2.24 will get me to 2160 rpm at the same speed (vs 3.07)
The question is...is there enough power to push me through the air @ that rpm, which is why I think additional power is needed.
Doesnt make sense to lower the rpm if it will require more throttle to keep it at the same speed.
Propane?
Ron Burgundy
1982 300SD - 310,XXX - Orient Red
Currently giving me 29-31, which gives me 500-550 per tank (17-18 gal)....21 gal total right?
How about a 2.24 or 2.47 rear end?
If 70 mph = 3000 rpm, dumb math tells me that a 2.24 will get me to 2160 rpm at the same speed (vs 3.07)
The question is...is there enough power to push me through the air @ that rpm, which is why I think additional power is needed.
Doesnt make sense to lower the rpm if it will require more throttle to keep it at the same speed.
Propane?
Ron Burgundy
1982 300SD - 310,XXX - Orient Red
The only way to go is to reduce weight and improve aerodynamics. Or get a better engine. And getting a 190d is a shortcut to all that. You'll be lucky to get 30mpg with all the effort on a 617 126.
Though the random thought of what mpg an om602 would get in a 126 comes up. Sounds doable too.
More power = use more fuel. Oh, and propane is fuel. Presumably it also costs money/takes space.
The only way to go is to reduce weight and improve aerodynamics. Or get a better engine. And getting a 190d is a shortcut to all that. You'll be lucky to get 30mpg with all the effort on a 617 126.
Though the random thought of what mpg an om602 would get in a 126 comes up. Sounds doable too.
Hope some of this helps out, welcome to the forum!
82 300SD aka The Flyin Pumpkin (Gone): 7.5mm super M-pump, T3 60 trim turbo, Coldish air intake, A/W intercooler, propane injection, SW Boost and EGT gauges, Monark 265 nozzles, ported/polished cylinder head.
84 Euro 300D 4 sp: White with black trunk and hood. Blue cloth interior. Manual everything. 300DT front swaybar. C320 17" wheels. Now with the Flyin Pumpkins engine!
I've had a best so far of just over 33mpg at steady 70ish driving on the highway, going across Washington in my '82 300SD. I have 225/65R16 tires pumped up to 40psi running the stock 3.07 rear diff. That milage is with propane on. My car has been lowered a bit, but no skinny tires for me. I enjoy taking my corners at an exciting clip. You could do a different rear diff ratio, I found the taller tires were cheaper than a diff (got the tires for just about free...). I'd recommend either the 2.66 or 2.88 rear diff, but neither one of those are super easy to find. My speedo is off by 11% with the taller tires, the milage is with corrected odo readings. These cars are heavy, 4000 lbs across the truck scale with me in it at a half tank of fuel. If you don't really, really need all the interior bits, you could probably shed some pounds, but I don't feel you're going to get significant wieght loss in the 126 chassis. If you find some wieght to lose though, please, feel free to share it with us! Hope some of this helps out, welcome to the forum!
82 300SD aka The Flyin Pumpkin (Gone): 7.5mm super M-pump, T3 60 trim turbo, Coldish air intake, A/W intercooler, propane injection, SW Boost and EGT gauges, Monark 265 nozzles, ported/polished cylinder head.
84 Euro 300D 4 sp: White with black trunk and hood. Blue cloth interior. Manual everything. 300DT front swaybar. C320 17" wheels. Now with the Flyin Pumpkins engine!
1987 300SDL 6spd manual om606.962 swap project
1985 300td euro 5spd wagon running
willbhere4u
04-29-2010, 08:43 PM #8Every little bit helps!!! weight, aerodynamics and performance personally I would make sure it in tip top tune with rebuilt injectors and a valve adjustment and a free flowing exhaust and intake!
1987 300SDL 6spd manual om606.962 swap project
1985 300td euro 5spd wagon running
The car is in good shape, purchased with full service records all the way back to '81. I've been going through the car for the last few months cleaning everything up. All fluids, brakes, tires, bushings and whatnot.
If i can keep the same fuel consumption with a taller diff I think I can get to what I'm shooting for.
I thought I would get ideas from you guys, but it seems like some here are wet blankets about it...
Let's take the current 29 MPG and multiply by the difference in rpm with the taller diff (3.07/2.24=1.37*29=39 theoretical MPG)
39*19 gallons=741 miles - again, dumb math but the possibility is there.
I'm flushing the engine with oil/filer changes every 2000 miles then every 1000 miles to check for oil consumption and in order to change over to synthetic. Every little bit helps right?
I think I'll start with looking around for a diff from a V8...new Bilstein shocks are in the works to go with the cut spring (starting with one coil)
Anyone think I can win a gumball rally by going 700 miles between stops?
Ron Burgundy
1982 300SD - 310,XXX - Orient Red
We all know that once at speed weight is a minimal issue, the majority of the power is used to overcome drag.
The car is in good shape, purchased with full service records all the way back to '81. I've been going through the car for the last few months cleaning everything up. All fluids, brakes, tires, bushings and whatnot.
If i can keep the same fuel consumption with a taller diff I think I can get to what I'm shooting for.
I thought I would get ideas from you guys, but it seems like some here are wet blankets about it...
Let's take the current 29 MPG and multiply by the difference in rpm with the taller diff (3.07/2.24=1.37*29=39 theoretical MPG)
39*19 gallons=741 miles - again, dumb math but the possibility is there.
I'm flushing the engine with oil/filer changes every 2000 miles then every 1000 miles to check for oil consumption and in order to change over to synthetic. Every little bit helps right?
I think I'll start with looking around for a diff from a V8...new Bilstein shocks are in the works to go with the cut spring (starting with one coil)
Anyone think I can win a gumball rally by going 700 miles between stops?
Ron Burgundy
1982 300SD - 310,XXX - Orient Red
(04-29-2010, 06:47 PM)arceo_1 Doesnt make sense to lower the rpm if it will require more throttle to keep it at the same speed.
This to me is the real question here. My understanding is that you want the engine to be working at it's maximum torque RPM. It's at that RPM that you're most effectively using fuel.
So if max torque is 2500 RPM, then you want a taller gearing in the rear end or increase tire size and or lower your cruising speed to maintain that RPM.
Alternately, if you're really just looking for range, then add a second fuel tank.
And if you're going to get tweaky, then swap out the automatic transmission for a manual, upgrade your turbo to something more modern and efficient,
put a big teardrop faring on the rear of the car like the hypermilers do.
-------------
'84 G-Wagen turbodiesel
'75 240D 4-Speed
(04-29-2010, 06:47 PM)arceo_1 Doesnt make sense to lower the rpm if it will require more throttle to keep it at the same speed.
This to me is the real question here. My understanding is that you want the engine to be working at it's maximum torque RPM. It's at that RPM that you're most effectively using fuel.
So if max torque is 2500 RPM, then you want a taller gearing in the rear end or increase tire size and or lower your cruising speed to maintain that RPM.
Alternately, if you're really just looking for range, then add a second fuel tank.
And if you're going to get tweaky, then swap out the automatic transmission for a manual, upgrade your turbo to something more modern and efficient,
put a big teardrop faring on the rear of the car like the hypermilers do.
-------------
'84 G-Wagen turbodiesel
'75 240D 4-Speed
(04-29-2010, 11:55 PM)Syncro_G(04-29-2010, 06:47 PM)arceo_1 Doesnt make sense to lower the rpm if it will require more throttle to keep it at the same speed.
This to me is the real question here. My understanding is that you want the engine to be working at it's maximum torque RPM. It's at that RPM that you're most effectively using fuel.
So if max torque is 2500 RPM, then you want a taller gearing in the rear end or increase tire size and or lower your cruising speed to maintain that RPM.
Alternately, if you're really just looking for range, then add a second fuel tank.
And if you're going to get tweaky, then swap out the automatic transmission for a manual, upgrade your turbo to something more modern and efficient,
put a big teardrop faring on the rear of the car like the hypermilers do.
Ron Burgundy
1982 300SD - 310,XXX - Orient Red
(04-29-2010, 11:55 PM)Syncro_G(04-29-2010, 06:47 PM)arceo_1 Doesnt make sense to lower the rpm if it will require more throttle to keep it at the same speed.
This to me is the real question here. My understanding is that you want the engine to be working at it's maximum torque RPM. It's at that RPM that you're most effectively using fuel.
So if max torque is 2500 RPM, then you want a taller gearing in the rear end or increase tire size and or lower your cruising speed to maintain that RPM.
Alternately, if you're really just looking for range, then add a second fuel tank.
And if you're going to get tweaky, then swap out the automatic transmission for a manual, upgrade your turbo to something more modern and efficient,
put a big teardrop faring on the rear of the car like the hypermilers do.
Ron Burgundy
1982 300SD - 310,XXX - Orient Red
You should shoot for about 2500rpm at cruising speed any lower and it will probably lower mileage as you will need more throttle input to cruise
1987 300SDL 6spd manual om606.962 swap project
1985 300td euro 5spd wagon running
willbhere4u
04-30-2010, 12:33 PM #13Look for a front bumper off of a w126 560sel some of them already have a front air damn and the euro light should also help a little bit as they are flush to the body and look nicer!!!
You should shoot for about 2500rpm at cruising speed any lower and it will probably lower mileage as you will need more throttle input to cruise
1987 300SDL 6spd manual om606.962 swap project
1985 300td euro 5spd wagon running
GREASY_BEAST
04-30-2010, 01:31 PM #14Look at this thread. It has most of the gearing and engine-related information you are looking for.
about 4 years ago I took a trip to the mid-atlantic states, ran with traffic on the way south and got about 27 MPG in the stock 300TD. On the way home, I was trying to keep the marginal radiator on the job, so I slowed down to 2300-2500 RPM. not only did the engine stay cooler, but I got 34.9 MPG.... at speeds above 55mph more and more fuel is used to push the air out of the way.. so I would say find a way to cheat the wind, and you will win some gains at the pump. I doubt most people are willing to drive at such a slow pace just to get good mileage.. I don't.
if you want better mileage all you have to do is slow down...
about 4 years ago I took a trip to the mid-atlantic states, ran with traffic on the way south and got about 27 MPG in the stock 300TD. On the way home, I was trying to keep the marginal radiator on the job, so I slowed down to 2300-2500 RPM. not only did the engine stay cooler, but I got 34.9 MPG.... at speeds above 55mph more and more fuel is used to push the air out of the way.. so I would say find a way to cheat the wind, and you will win some gains at the pump. I doubt most people are willing to drive at such a slow pace just to get good mileage.. I don't.
(04-30-2010, 03:14 PM)Jdmills if you want better mileage all you have to do is slow down...
Good aero does the same thing.
GREASY_BEAST
04-30-2010, 09:33 PM #16(04-30-2010, 03:14 PM)Jdmills if you want better mileage all you have to do is slow down...
Good aero does the same thing.
The motor is an air pump that needs to be made as efficient as possible.... easy fixes: perfect injectors, perfect injector pump, synthetic oil, low resistance air filter (K&N), low resistance exhaust, always run at max volumetric efficiency rpm.
The driveline is a parasite that needs to have it's appetite trimmed... easy fixes: synthetic fluids in transmission & differential, a well adjusted transmission
The Car is a resistance to the wind that needs to be reduced... easy fixes: keep the car waxed, antenna down, lowering springs
The wheels resist turning and need to be free... easy fixes: wheel bearings adjusted correctly or almost loose, synthetic grease, brakes without drag
The tires want to bite the road and that bite needs to be changed... easy fixes: low rolling resistant tires
With all that you will hove spent $3+K and get 2-3mpg overall improvement... there is no way to get a large 2-3 ton blunt object through the air at 70mph and 35mpg. Go do the math... how much energy it takes to move that mass through the air, the efficiency of the engine minus the loss of driveline, wheels, tires, etc. and you will find it neigh to impossible in any current configuration.
Check what MB has done with the new diesels to get 35mpg: lighter weigh, more aerodynamic design, seven speed transmission, electronic fuel management with seven to 20 injections on every stroke, variable turbo, multiple valves per cylinder, etc. You and I can't even compete. So I remain happy with 24-25 in town and 27-30 on the road.
NRK
86 300SDL
64 230SL
You have to think differently...
The motor is an air pump that needs to be made as efficient as possible.... easy fixes: perfect injectors, perfect injector pump, synthetic oil, low resistance air filter (K&N), low resistance exhaust, always run at max volumetric efficiency rpm.
The driveline is a parasite that needs to have it's appetite trimmed... easy fixes: synthetic fluids in transmission & differential, a well adjusted transmission
The Car is a resistance to the wind that needs to be reduced... easy fixes: keep the car waxed, antenna down, lowering springs
The wheels resist turning and need to be free... easy fixes: wheel bearings adjusted correctly or almost loose, synthetic grease, brakes without drag
The tires want to bite the road and that bite needs to be changed... easy fixes: low rolling resistant tires
With all that you will hove spent $3+K and get 2-3mpg overall improvement... there is no way to get a large 2-3 ton blunt object through the air at 70mph and 35mpg. Go do the math... how much energy it takes to move that mass through the air, the efficiency of the engine minus the loss of driveline, wheels, tires, etc. and you will find it neigh to impossible in any current configuration.
Check what MB has done with the new diesels to get 35mpg: lighter weigh, more aerodynamic design, seven speed transmission, electronic fuel management with seven to 20 injections on every stroke, variable turbo, multiple valves per cylinder, etc. You and I can't even compete. So I remain happy with 24-25 in town and 27-30 on the road.
NRK
86 300SDL
64 230SL
1987 300D Sturmmachine
1991 300D Nearly Perfect
1985 300D Weekend/Camping/Dog car
1974 L508D Motoroam Monarch "NightMare"
OBK #42
I got 32mpg driving from ATL to FL in a hurricane at 35mph on the interstate. Was a personal best for me. Don't expect great MPG achievements with the 61x engines and old german steel (as FI calls it).
1987 300D Sturmmachine
1991 300D Nearly Perfect
1985 300D Weekend/Camping/Dog car
1974 L508D Motoroam Monarch "NightMare"
OBK #42
tall order to get 35 and go fast though. Id love to see your improvments, ive been very interested in MPG improvements as well. Problem is that I have a huge lead foot, and cannot keep the speed down.
Saw a guy in a TDI the other day doing that ecomodder stuff that annoys the hell out of truckers, following along right in their slip stream barely in view.
You should try that with no mods and see what kind of improvement that makes on a 617 powered SD over distance. I just can't bring myself to do that for more than a few miles.
1974 240D 617 turbo swap, W201 5-speed, in the works project
1983 240D 616 stock, DD
1989 Chevy Astro, 617 turbo swap, T5 5-speed, 4.56 diff, work van
thin tall tires you have listed, reducing drag underneath as well. This was discussed in another thread over in body mods, but if you could encapsulate the engine compartment and maybe some of the driveshaft tunnel and rear suspension area, you might cut down on some of that drag as well.
tall order to get 35 and go fast though. Id love to see your improvments, ive been very interested in MPG improvements as well. Problem is that I have a huge lead foot, and cannot keep the speed down.
Saw a guy in a TDI the other day doing that ecomodder stuff that annoys the hell out of truckers, following along right in their slip stream barely in view.
You should try that with no mods and see what kind of improvement that makes on a 617 powered SD over distance. I just can't bring myself to do that for more than a few miles.
1974 240D 617 turbo swap, W201 5-speed, in the works project
1983 240D 616 stock, DD
1989 Chevy Astro, 617 turbo swap, T5 5-speed, 4.56 diff, work van
Flushing out the engine with a few frequent oil changes in order to start using synthetics, including trans and diff.
I just went from 215.65.15 to 205.60.15 tires (Goodyear Eagle GT), not as tall but thinner. Although this went in the opposite direction of the taller gearing idea, the size is closer to the original 195.something.14's. I also think they weigh less, and the small size decreases rotating mass. Currently running 40 PSI.
Lower the car by approx an inch. Tape off the lower opening in the bumper, nascar style. Then depending on what engine temps do some of the upper grill (probably not though).
Take out the spare tire and empty the trunk. This will be the only weight saving I can live with.
I will start this weekend with fresh engine, trans, and diff fluids. I've gone 4 tanks on this oil (approx 2K miles).
When the new shocks come in I will do the lowering and get an alignment. I'll be posting results.
Ron Burgundy
1982 300SD - 310,XXX - Orient Red
Okay, this is the plan...
Flushing out the engine with a few frequent oil changes in order to start using synthetics, including trans and diff.
I just went from 215.65.15 to 205.60.15 tires (Goodyear Eagle GT), not as tall but thinner. Although this went in the opposite direction of the taller gearing idea, the size is closer to the original 195.something.14's. I also think they weigh less, and the small size decreases rotating mass. Currently running 40 PSI.
Lower the car by approx an inch. Tape off the lower opening in the bumper, nascar style. Then depending on what engine temps do some of the upper grill (probably not though).
Take out the spare tire and empty the trunk. This will be the only weight saving I can live with.
I will start this weekend with fresh engine, trans, and diff fluids. I've gone 4 tanks on this oil (approx 2K miles).
When the new shocks come in I will do the lowering and get an alignment. I'll be posting results.
Ron Burgundy
1982 300SD - 310,XXX - Orient Red
I don't think I've put 100 miles on it yet, so no updates on mileage with new T3/T4OE turbo. I think you are heading the right direction though for getting better milage. Keep us posted on the results!
82 300SD aka The Flyin Pumpkin (Gone): 7.5mm super M-pump, T3 60 trim turbo, Coldish air intake, A/W intercooler, propane injection, SW Boost and EGT gauges, Monark 265 nozzles, ported/polished cylinder head.
84 Euro 300D 4 sp: White with black trunk and hood. Blue cloth interior. Manual everything. 300DT front swaybar. C320 17" wheels. Now with the Flyin Pumpkins engine!
I'm looking forward to seeing what kind of gains you get. I'm pretty happy with my milage so far... but I also just swapped in a bigger turbo this weekend. I don't think I've put 100 miles on it yet, so no updates on mileage with new T3/T4OE turbo.
I think you are heading the right direction though for getting better milage. Keep us posted on the results!
82 300SD aka The Flyin Pumpkin (Gone): 7.5mm super M-pump, T3 60 trim turbo, Coldish air intake, A/W intercooler, propane injection, SW Boost and EGT gauges, Monark 265 nozzles, ported/polished cylinder head.
84 Euro 300D 4 sp: White with black trunk and hood. Blue cloth interior. Manual everything. 300DT front swaybar. C320 17" wheels. Now with the Flyin Pumpkins engine!
(05-01-2010, 09:21 PM)arceo_1 looks great....
An explanation:
There is a chart in that thread which states the BSFC (brake specific fuel consumption) of the standard OM617 engine. This chart has lines of constant horsepower, as well as a max power line (draw an imaginary vertical line on which to guess demand), and fuel consumption regions plotted on it. If you could get your aerodynamics situated such that you have enough power at around 2250rpm and ~65% engine load to push the car through the wind at your desired cruising speed, you should see an MPG gain by running at this speed. Aerodynamic drag is the dominant resistance at highway speed. Tires and drivetrain contribute, but air is the real killer. If you could make the car more slippery, then you could see some real gains, but the effort required to do so on this bodystyle far outweighs the potential gain. You would be better off starting from scratch (I.E a pile of tubing and driveline components).
EDIT: Basically, at this gearing level, you have 45-50hp to work with. The challenge is to make the car go as fast as you can with this power output, at 2250rpm.
GREASY_BEAST
05-04-2010, 09:30 PM #24(05-01-2010, 09:21 PM)arceo_1 looks great....
An explanation:
There is a chart in that thread which states the BSFC (brake specific fuel consumption) of the standard OM617 engine. This chart has lines of constant horsepower, as well as a max power line (draw an imaginary vertical line on which to guess demand), and fuel consumption regions plotted on it. If you could get your aerodynamics situated such that you have enough power at around 2250rpm and ~65% engine load to push the car through the wind at your desired cruising speed, you should see an MPG gain by running at this speed. Aerodynamic drag is the dominant resistance at highway speed. Tires and drivetrain contribute, but air is the real killer. If you could make the car more slippery, then you could see some real gains, but the effort required to do so on this bodystyle far outweighs the potential gain. You would be better off starting from scratch (I.E a pile of tubing and driveline components).
EDIT: Basically, at this gearing level, you have 45-50hp to work with. The challenge is to make the car go as fast as you can with this power output, at 2250rpm.
(05-04-2010, 09:30 PM)GREASY_BEAST(05-01-2010, 09:21 PM)arceo_1 looks great....
An explanation:
There is a chart in that thread which states the BSFC (brake specific fuel consumption) of the standard OM617 engine. This chart has lines of constant horsepower, as well as a max power line (draw an imaginary vertical line on which to guess demand), and fuel consumption regions plotted on it. If you could get your aerodynamics situated such that you have enough power at around 2250rpm and ~65% engine load to push the car through the wind at your desired cruising speed, you should see an MPG gain by running at this speed. Aerodynamic drag is the dominant resistance at highway speed. Tires and drivetrain contribute, but air is the real killer. If you could make the car more slippery, then you could see some real gains, but the effort required to do so on this bodystyle far outweighs the potential gain. You would be better off starting from scratch (I.E a pile of tubing and driveline components).
EDIT: Basically, at this gearing level, you have 45-50hp to work with. The challenge is to make the car go as fast as you can with this power output, at 2250rpm.
Hmm, interesting. Is this why 55mph give you right abour 2350-2400rpm?
Was that not the legal limit back then?
The National Maximum Speed Law in the United States was a provision of the 1974 Emergency Highway Energy Conservation Act that prohibited speed limits higher than 55 mph (90 km/h). This law was modified in 1987 to allow 65 mph (105 km/h) limits on certain roads.
Sounds like I need to gain about 20-25% power in order to run the type of gearing that could yield max MPG.
Better stock up on duck tape....
Let me introduce Ron Burgundy...
Ron Burgundy
1982 300SD - 310,XXX - Orient Red
(05-04-2010, 09:30 PM)GREASY_BEAST(05-01-2010, 09:21 PM)arceo_1 looks great....
An explanation:
There is a chart in that thread which states the BSFC (brake specific fuel consumption) of the standard OM617 engine. This chart has lines of constant horsepower, as well as a max power line (draw an imaginary vertical line on which to guess demand), and fuel consumption regions plotted on it. If you could get your aerodynamics situated such that you have enough power at around 2250rpm and ~65% engine load to push the car through the wind at your desired cruising speed, you should see an MPG gain by running at this speed. Aerodynamic drag is the dominant resistance at highway speed. Tires and drivetrain contribute, but air is the real killer. If you could make the car more slippery, then you could see some real gains, but the effort required to do so on this bodystyle far outweighs the potential gain. You would be better off starting from scratch (I.E a pile of tubing and driveline components).
EDIT: Basically, at this gearing level, you have 45-50hp to work with. The challenge is to make the car go as fast as you can with this power output, at 2250rpm.
Hmm, interesting. Is this why 55mph give you right abour 2350-2400rpm?
Was that not the legal limit back then?
The National Maximum Speed Law in the United States was a provision of the 1974 Emergency Highway Energy Conservation Act that prohibited speed limits higher than 55 mph (90 km/h). This law was modified in 1987 to allow 65 mph (105 km/h) limits on certain roads.
Sounds like I need to gain about 20-25% power in order to run the type of gearing that could yield max MPG.
Better stock up on duck tape....
Let me introduce Ron Burgundy...
Ron Burgundy
1982 300SD - 310,XXX - Orient Red
An aeronautical engineer named Phil Knox took a Toyota T100 pickup truck, and with extensive aeromods, increased its highway fuel economy from 25 mpg to 32 mpg, with no other modifications. Do a google search for some articles on this.
Weight reduction would be the next place to look, except that weight reduction is going to cost far too much for appreciable gains with a Benz. Are you willing to spend thousands of dollars? Reducing your weight by 1,000 lbs would probably give you an extra 25% to fuel economy in the city from stock, maybe 10% on the highway.
Gearing will have a significant impact. Without any other changes, going to a 2.65 ratio would probably give you a 10% gain on the highway, but may be detrimental to fuel economy in the city due to increased throttle usage for a desired amount of acceleration; this can be mitigated with a driving style that uses high load under acceleration and lots of coasting; drive in such a way to minimize the use of your brakes and coast as much as possible. The best way to find out how your fuel economy in various operating conditions will be impacted would be to obtain a BSFC curve of your engine; later, I will post the math relating to vehicle dynamics so you can get an idea of what goes on. Gearing would compliment aerodynamic drag reduction nicely; your top speed would increase tremendously as a result of both! With extreme drag reduction on the order of basjoos Honda Civic and the gearing to accomodate it, your 300 SD would have no problem reaching 150 mph with its anemic stock engine; although its acceleration from 0-60 mph would not be changed much, acceleration above 60 mph would improve dramatically with drag reduction.
Low rolling resistance tires is another obvious place. Installing Goodyear Assurance Fuel Max 205/65R15 tires on my 300 SDL has increased the fuel economy at a steady 70 mph from 28.5 mpg to 30.1 mpg(warning: I did not measure wind speeds on my trip so any headwinds, tail winds, or cross winds could have affected the accuracy).
Synthetic engine and transmission oils both used would have a 1-2% impact combined. Every little bit helps.
Getting 40 mpg highway at 70 mph is not out of the question with about $2,000 in investments and lots of work.
I'm still in the planning stages for my 300 SDL. I want performance AND fuel economy while running on WVO. Efficiency mods + Myna are calling my name... I'm not going to pursue weight reduction, although it would be nice. Gearing and aerodynamics will be my focus for fuel economy... and it will mostly be on the highway. The car will still be a 3,800 lb tank and still get less than 20 mpg in the city; I'll have to live with that, but 45 mpg highway is possible, and I'm planning on about 220 horsepower and 290 lb-ft of torque with performance upgrades for when I want to slam my foot to the floor...
The Toecutter
05-06-2010, 06:35 AM #28The first place to start would be aerodynamics. People at sites like gassavers.org and ecomodder have done aerodynamic mods to their cars with dramatic results. Member basjoos has a Honda Civic that can exceed 90 mpg at 55 mph, 40 mpg at 90 mph. Corrugated plastic is a commonly used material due to its low cost and the fact that it is easy to bend and mount. Cardboard mockups are commonly tested first. If you want it to look professional, as if it was part of the car from the factory, you will have to use fiberglass or steel and will have your work cut out for you; coroplast looks tacky, but it works. The gain in economy from your aeromods will depend on what you do. Metrompg.com is a good source of info; wheel skirts alone will give you a 3% gain from what I've read. Other modifications, like a partial grill block, side skirts with front air dam, reduced ride height(optimum for reduced drag ~3 inches ground clearance, but for practical reasons you will probably need more than that), removing passenger mirror, thinner tires, all add up. Depending upon the extent of your aerodynamic mods, this could net you +40% fuel economy on the highway and +5% in the city. If your mods are modest, say blocking half of the grill in the right places, rear wheel skirts, no passenger mirror, ride height lowered to 5 inches, and skinnier tires, you'll probably see a 10% gain from that alone. The big gains will come from an extension of the rear roofline that maintains laminar flow so as to reduce turbulence generated, but you will acquire blind spot issues.
An aeronautical engineer named Phil Knox took a Toyota T100 pickup truck, and with extensive aeromods, increased its highway fuel economy from 25 mpg to 32 mpg, with no other modifications. Do a google search for some articles on this.
Weight reduction would be the next place to look, except that weight reduction is going to cost far too much for appreciable gains with a Benz. Are you willing to spend thousands of dollars? Reducing your weight by 1,000 lbs would probably give you an extra 25% to fuel economy in the city from stock, maybe 10% on the highway.
Gearing will have a significant impact. Without any other changes, going to a 2.65 ratio would probably give you a 10% gain on the highway, but may be detrimental to fuel economy in the city due to increased throttle usage for a desired amount of acceleration; this can be mitigated with a driving style that uses high load under acceleration and lots of coasting; drive in such a way to minimize the use of your brakes and coast as much as possible. The best way to find out how your fuel economy in various operating conditions will be impacted would be to obtain a BSFC curve of your engine; later, I will post the math relating to vehicle dynamics so you can get an idea of what goes on. Gearing would compliment aerodynamic drag reduction nicely; your top speed would increase tremendously as a result of both! With extreme drag reduction on the order of basjoos Honda Civic and the gearing to accomodate it, your 300 SD would have no problem reaching 150 mph with its anemic stock engine; although its acceleration from 0-60 mph would not be changed much, acceleration above 60 mph would improve dramatically with drag reduction.
Low rolling resistance tires is another obvious place. Installing Goodyear Assurance Fuel Max 205/65R15 tires on my 300 SDL has increased the fuel economy at a steady 70 mph from 28.5 mpg to 30.1 mpg(warning: I did not measure wind speeds on my trip so any headwinds, tail winds, or cross winds could have affected the accuracy).
Synthetic engine and transmission oils both used would have a 1-2% impact combined. Every little bit helps.
Getting 40 mpg highway at 70 mph is not out of the question with about $2,000 in investments and lots of work.
I'm still in the planning stages for my 300 SDL. I want performance AND fuel economy while running on WVO. Efficiency mods + Myna are calling my name... I'm not going to pursue weight reduction, although it would be nice. Gearing and aerodynamics will be my focus for fuel economy... and it will mostly be on the highway. The car will still be a 3,800 lb tank and still get less than 20 mpg in the city; I'll have to live with that, but 45 mpg highway is possible, and I'm planning on about 220 horsepower and 290 lb-ft of torque with performance upgrades for when I want to slam my foot to the floor...
(05-06-2010, 06:35 AM)The Toecutter but 45 mpg highway is possible
Not with an OM61x. The thermal efficiency needed simply isn't there.
ForcedInduction
05-06-2010, 06:46 AM
#29
(05-06-2010, 06:35 AM)The Toecutter but 45 mpg highway is possible
Not with an OM61x. The thermal efficiency needed simply isn't there.
(05-06-2010, 06:46 AM)ForcedInduction(05-06-2010, 06:35 AM)The Toecutter but 45 mpg highway is possible
Not with an OM61x. The thermal efficiency needed simply isn't there.
Do you have available a BSFC map of the engine? If so, i'd love to have it so I can go through the math, to either support or deny my assertion.
My 300 SDL's engine has a higher thermal efficiency than the OM617 found in the 300SD. I did go through some math on mine, but had to make some assumption's about my engine's efficiency.
If you reduce the combined rolling, air, and mechanical drag of a car at the speed he gets 30 mpg by two-thirds, even with the drop of thermal efficiency present in the engine from reduced load, gaining another one-half to highway gas mileage doesn't seem out of the question. Getting a reduction in drag to that extent in that car would require extensive aerodynamic modifications though, on the order of basjoos' Honda Civic I mentioned earlier.
My 300 SDL, while it gets ~25-30 mpg on a highway cruise keeping with the flow of traffic, and < 20 in town, it had no problem getting more than 40 mpg on a trip from Corpus Christi, TX, to Falfurrias, TX. How? I kept it at a steady 50 mph the entire trip. I had similar results trying a different road trip at this speed with a gasoline Ford Contour as well, that normally got ~28 mpg at 70 mph.
Didn't the C111-III use a modified version of the OM617 engine? It still achieved more than 14 mpg at 195 mph, when the gasoline cars that can reach that speed and maintain it are hard-pressed to exceed 5 mpg at that speed(even with their engines at near-optimum thermal efficiency due to the load present). Given that the C111-III has about half of the drag of the typical "supercar", and a diesel engine that is about twice as efficient as an Otto Cycle engine, this varience in mpg makes sense.
Also notice the dorsal ridge on the C111-III; the functionality of that is to help provide stability at speed and during crosswinds. A lot can be learned from that car.
The Toecutter
05-06-2010, 05:11 PM #30(05-06-2010, 06:46 AM)ForcedInduction(05-06-2010, 06:35 AM)The Toecutter but 45 mpg highway is possible
Not with an OM61x. The thermal efficiency needed simply isn't there.
Do you have available a BSFC map of the engine? If so, i'd love to have it so I can go through the math, to either support or deny my assertion.
My 300 SDL's engine has a higher thermal efficiency than the OM617 found in the 300SD. I did go through some math on mine, but had to make some assumption's about my engine's efficiency.
If you reduce the combined rolling, air, and mechanical drag of a car at the speed he gets 30 mpg by two-thirds, even with the drop of thermal efficiency present in the engine from reduced load, gaining another one-half to highway gas mileage doesn't seem out of the question. Getting a reduction in drag to that extent in that car would require extensive aerodynamic modifications though, on the order of basjoos' Honda Civic I mentioned earlier.
My 300 SDL, while it gets ~25-30 mpg on a highway cruise keeping with the flow of traffic, and < 20 in town, it had no problem getting more than 40 mpg on a trip from Corpus Christi, TX, to Falfurrias, TX. How? I kept it at a steady 50 mph the entire trip. I had similar results trying a different road trip at this speed with a gasoline Ford Contour as well, that normally got ~28 mpg at 70 mph.
Didn't the C111-III use a modified version of the OM617 engine? It still achieved more than 14 mpg at 195 mph, when the gasoline cars that can reach that speed and maintain it are hard-pressed to exceed 5 mpg at that speed(even with their engines at near-optimum thermal efficiency due to the load present). Given that the C111-III has about half of the drag of the typical "supercar", and a diesel engine that is about twice as efficient as an Otto Cycle engine, this varience in mpg makes sense.
Also notice the dorsal ridge on the C111-III; the functionality of that is to help provide stability at speed and during crosswinds. A lot can be learned from that car.
(05-06-2010, 05:11 PM)The Toecutter Do you have available a BSFC map of the engine?
(04-30-2010, 01:31 PM)GREASY_BEAST Look at this thread. It has most of the gearing and engine-related information you are looking for.
(05-06-2010, 05:11 PM)The Toecutter Also notice the dorsal ridge on the C111-III; the functionality of that is to help provide stability at speed and during crosswinds. A lot can be learned from that car.
The bold part makes no sense.
GREASY_BEAST
05-06-2010, 05:30 PM #31(05-06-2010, 05:11 PM)The Toecutter Do you have available a BSFC map of the engine?
(04-30-2010, 01:31 PM)GREASY_BEAST Look at this thread. It has most of the gearing and engine-related information you are looking for.
(05-06-2010, 05:11 PM)The Toecutter Also notice the dorsal ridge on the C111-III; the functionality of that is to help provide stability at speed and during crosswinds. A lot can be learned from that car.
The bold part makes no sense.
(05-06-2010, 05:30 PM)GREASY_BEAST(05-06-2010, 05:11 PM)The Toecutter Do you have available a BSFC map of the engine?
(04-30-2010, 01:31 PM)GREASY_BEAST Look at this thread. It has most of the gearing and engine-related information you are looking for.
(05-06-2010, 05:11 PM)The Toecutter Also notice the dorsal ridge on the C111-III; the functionality of that is to help provide stability at speed and during crosswinds. A lot can be learned from that car.
The bold part makes no sense.
That info was also for full-load, which is nearly useless for steady state highway cruising. However, the proper info is certainly there for me to calculate theoretical fuel economy, at what would be a theoretical top speed.
I have studied BSFC maps for other vehicles, like the Golf TDI, and the plot was usually a line depicting full load RPM vs Torque, with either g/kWh or percentage thermal efficiency overlayed on a map that composed everything underneath that full load rpm vs torque line, so that you could see the efficiency at all or nearly all of the engine's operating points.
Also, a properly designed fin can actually help mitigate crosswinds, so long as it is shaped in such a way that the crosswinds are directed around it, instead of it acting like a sail as you would expect it to(and depending on application, often acts as a sail in many airplanes). The dorsal fin on the Tatra T87 was built specifically for stability during crosswinds, as an example; the complex intereaction of the air and the fin helped keep the nose of the vehicle pointed straight. I would not dare make one for my car unless I had windtunnel access and knew what I was doing when using one. Subtle, almost imperceptable changes to the shape can have significant effects on how the air behaves.
*update*
I retract my earlier statement about that thread not having a BSFC map. I opened the same thread on my PS3 and an image in post #8 showed up, that did not show up on my computer when I looked at the tread weeks earlier. Score!
Now I have the data that I need. Time to get number crunching.
The Toecutter
05-06-2010, 05:47 PM #32(05-06-2010, 05:30 PM)GREASY_BEAST(05-06-2010, 05:11 PM)The Toecutter Do you have available a BSFC map of the engine?
(04-30-2010, 01:31 PM)GREASY_BEAST Look at this thread. It has most of the gearing and engine-related information you are looking for.
(05-06-2010, 05:11 PM)The Toecutter Also notice the dorsal ridge on the C111-III; the functionality of that is to help provide stability at speed and during crosswinds. A lot can be learned from that car.
The bold part makes no sense.
That info was also for full-load, which is nearly useless for steady state highway cruising. However, the proper info is certainly there for me to calculate theoretical fuel economy, at what would be a theoretical top speed.
I have studied BSFC maps for other vehicles, like the Golf TDI, and the plot was usually a line depicting full load RPM vs Torque, with either g/kWh or percentage thermal efficiency overlayed on a map that composed everything underneath that full load rpm vs torque line, so that you could see the efficiency at all or nearly all of the engine's operating points.
Also, a properly designed fin can actually help mitigate crosswinds, so long as it is shaped in such a way that the crosswinds are directed around it, instead of it acting like a sail as you would expect it to(and depending on application, often acts as a sail in many airplanes). The dorsal fin on the Tatra T87 was built specifically for stability during crosswinds, as an example; the complex intereaction of the air and the fin helped keep the nose of the vehicle pointed straight. I would not dare make one for my car unless I had windtunnel access and knew what I was doing when using one. Subtle, almost imperceptable changes to the shape can have significant effects on how the air behaves.
*update*
I retract my earlier statement about that thread not having a BSFC map. I opened the same thread on my PS3 and an image in post #8 showed up, that did not show up on my computer when I looked at the tread weeks earlier. Score!
Now I have the data that I need. Time to get number crunching.
What you want to do is perfectly possible.
To all interested, feel free to make a spreadsheet using the info contained in my post below. All items in parenthesis are used as variables in the equations used.
Here is a projected model of arceo_1’s 300 SD.
Laden curb weight(M): 1700 kg
Stock Drag Coefficient(Cd): 0.36
Stock Frontal Area(A): 2.10
Tire Size: 205/60R15
Rolling Resistance Coefficient(Crr): 0.011 (typical of high performance tires)
Gear Ratio®: 3.07 (obtained from multiplying 4th gear, 1.00, by the final drive ratio of 3.07, and assuming 4th gear is used)
Driveline efficiency(TE): 82%, expressed in equation as 0.82 (assumes no synthetic lubricants)
Assumed Accessory Losses(Acc): 3,000 Watts (about 4 horsepower)
Note: The frontal area was estimated by taking the width and height of the car and multiplying by 0.8. This rough estimate of frontal area tends to be within about 5% of reality. The estimated driveline efficiency is typical for cars of that era, and the assumed accessory losses of 3 kW are a guess as to the average load being placed on the engine by the climate control, power steering, electronics, and other accessories at any given time, including the times that the accessories are demanding no load.
Knowing the tire size, this gives a wheel diameter of 24.7 inches, a wheel circumference of 77.6 inches, and 817 revolutions per mile(for the purposes of these calculations, will be expressed as 0.50766 revolutions per meter and denoted as T). This calculation was quickly obtained from the following tire size calculator:
http://www.miata.net/garage/tirecalc.html
The additional parameters that need to be expressed or calculated at various points to find the estimated fuel efficiency at various speeds are the following:
Velocity(V): expressed in meters per second
Force Air Drag(FD): expressed in Newtons
Force Rolling(FR): expressed in Newtons
Force Sliding(FS): sliding tire friction, expressed in Newtons, for a 1700 kg car, assumed as being 30 Newtons for simplicity’s sake
Wheel Power Required(WP): expressed in Watts
Engine Power Required(P): expressed in Watts
Air Density(Rho): 1.25 kg/m^3
Gravitational Constant(G): 9.8 N/kg
Engine Speed(RPM): expressed in revolutions per minute
Percentage thermal Efficiency(E): expressed in equations as a decimal
The equations we will use are the following:
FD = 0.5 * Rho * Cd * A * V^2
FR = G * Crr * M
WP = (FD + FR + FS) * V
P = WP / TE + Acc
RPM = V * T * 60 * R
To convert from miles per hour to meters per second, multiply the speed in mph by 0.44704.
So as not to lose anyone in confusion, I will model arceo_1’s car with the above baseline parameters at 70 mph. 70 mph is 31.3 m/s.
For FD, we get 462.7 Newtons. For FR, we get 183.3 Newtons. For WP, we get 21154 Watts. For P, we get 27798 Watts. For RPM, we discover that at 70 mph, the engine is turning at 2927 rpm.
The above paragraph tells use that the engine needs to put out 28.8 kW to maintain 70 mph, and is turning at 2927 rpm at that speed. Looking at the BSFC map posted in the thread that GREASYBEAST linked(post number 8), this tells us that our brake specific fuel consumption at that speed is about 310 g/kWh.
This means that 310 g/kWh of fuel is being consumed at 70 mph. A gallon of diesel fuel typically weighs 7.15 lbs(varies with temperature, but for purposes of the calculation, we will use 7.15 lbs), which is 3246 grams. There are 130500 BTUs of energy in a gallon of petro diesel, which is 38.2 kWh per gallon of petrodiesel. From this, we can calculate of percentage the fuel economy.
How?
At 70 mph, we will need to produce 28.8 kW from the engine for one hour to go 70 miles. We are consuming 0.0955 gallons of diesel fuel(310g/kWh divided by 3246 g/gallon) to generate 1 kWh of energy mechanically from the engine. To go 70 mph for one hour, or 70 miles, we need to generate 28.8 kWh from the engine. 0.0955 gallons/kWh * 28.8 kWh means we have used 2.7504 gallons of fuel to go 70 miles at 70 mph, or a fuel economy of 25.5 mpg!
25.5 mpg sounds pretty reasonable for a 300 SD at 70 mph, which is stock except for the tire size, don’t you think?
So what happens if we reduce the drag coefficient to 0.28 with some modest aerodynamic modifications(rear wheel skirts, smooth undertray, block off half of the grill, use a Kamm-style roof extension, lowered ground clearance to 4.5 inches), reduce the frontal area to 2.07 m^2 from the lowered ride height, swap in a 2.47 rear end, use synthetic lubricants to increase the efficiency of the driveline to 84%, and shave off 100 lbs of weight?
For FD, we get 356.6 Newtons. For FR, we get 178.4 Newtons. For WP, we get 17685 Watts. For P, we get 24053 Watts. At 70 mph, the engine is turning at 2355 rpm. This, 24 kW demanded at 2355 rpm, the BSFC map tells us that about 270 g/kWh is consumed. We have used exactly 2 gallons of fuel to do 70 mph for one hour, or 70 miles.
This is 35 mpg, right in line with the target by this topic’s creator!
BUT, there is much more than can be done with regard to aerodynamics and rolling resistance.
What happens if we not only keep the above proposed changes, but then reduce the drag coefficient further to 0.20 and reference area to 2.0 m^2 with some more extreme aerodynamic modifications(rear boat tail in place of Kamm roof extension, side skirts, cameras replacing side mirrors, front wheel spoilers, ect), reduce the frontal area to 2.0 m^2 from the mirror removal, and install Goodyear Assurance Fuel Max tires with a Crr of around 0.008 and size of 205/65R15 giving .492 revs per meter(there are much better tires for rolling resistance, some going as low as 0.006(!), but these are readily available for this wheel size and comparable in cost to normal tires and don’t sacrifice traction or tread wear characteristics)?
For FD, we get 244.9 Newtons. For FR, we get 129.7 Newtons. For WP, we get 12664 Watts. For P, we get 18076 Watts. At 70 mph, the engine is turning at 2282 rpm. This, 18 kW demanded at 2282 rpm, the BSFC map tells us that about 275 g/kWh is consumed. This is 1.531 gallons consumed to do 70 mph for 1 hour, which is 70 miles.
This equates to 45.7 mpg!
It is possible. Trust me, it is. Doing the work needed to get such a car to do this won’t be easy, but doable, yes. The C111-III streamliner would have had even better results thanks to its low weight, smaller frontal area, and taller final drive ratio.
Obviously, for WVO, B20, B100, and other alternative fuels, you are going to have to use a different energy amount per gallon to match the fuel used.
EPA cycle fuel economy will not be accurately reflected in the above calculations, although if you cruise down the interstate at a steady 70 mph, you probably will get similar results to those depicted here. These figures are for steady state cruising only. Math involving calculus is used when estimating fuel economy based on EPA driving cycles and it is probably above what most would be willing to go through on this board for a theoretical figure such as this.
I would also do my 300 SDL’s calculations in the exact same manner if I had a BSFC map for its specific engine; the link provided was for the OM617 engine, and not the one I have. The 300 SD engine is less efficient than the 6 cylinder used in my 300 SDL from what I have read on peachparts.com and elsewhere. I have done calculations for my 300 SDL(not posted) but without specific BSFC numbers; I am thus guessing in an educated manner. It is safe to say that my results will be at least as good as those projected with this 300 SD, if I can get the drag down to the appropriate levels.
Yes, 45 mpg *is* theoretically possible with this OM617 engine with the right modifications.
Whenever my 300 SDL’s body rusts away 15 years or more from now, I am probably going to use a VW chassis with custom low drag AND light weight fiberglass body for my engine, and gear the fucker for 200 mph. With say, 1,000 kg mass, 0.2 Cd, 1.4 m^2 frontal area, sticky racing tires with a Crr around 0.012, and 220 hp/290 lb-ft from engine mods, 60 MPG wouldn’t be out of the question, 0-60 mph in under 5 seconds would be doable, and somewhere around 190-200 mph top speed. Whether it would be stable at that speed, I would have to have a wind tunnel to have an idea beforehand... See the GM Precept(0.16 Cd, 2,600 lbs, 80 mpg, midsize car) on fuel economy, as such a figure of 70 mpg really isn't that far fetched.
Even if the engine from my 300 SDL is shoehorned into a Triumph Spitfire with no aerodynamic tweaks, the low frontal area, moderate drag coefficient(0.39 for Mk III, 1.4 m^2 frontal area, 1700 lbs laden weight with stock 350 lbs 4 cylinder engine), and being half the weight of a 300 SD would probably net 40+ mpg as well, and the thing would also haul some serious ass!
Another possibility would be using the engine and transmission from my 300 SDL on a 300 SL gullwing replica, just to keep it true to its Mercedes lineage. It would still be formidable in performance and fuel economy both, and it would definately have the pimp factor to attract the ladies.
The Toecutter
05-07-2010, 01:58 AM #33arceo_1, please absorb the information in this post. It will help you achieve your goals. Also, go to www.ecomodder.com for information on how to implement these changes, and for some starting info on how to design your aerodynamic extensions(eg. what books to read, ect.).
What you want to do is perfectly possible.
To all interested, feel free to make a spreadsheet using the info contained in my post below. All items in parenthesis are used as variables in the equations used.
Here is a projected model of arceo_1’s 300 SD.
Laden curb weight(M): 1700 kg
Stock Drag Coefficient(Cd): 0.36
Stock Frontal Area(A): 2.10
Tire Size: 205/60R15
Rolling Resistance Coefficient(Crr): 0.011 (typical of high performance tires)
Gear Ratio®: 3.07 (obtained from multiplying 4th gear, 1.00, by the final drive ratio of 3.07, and assuming 4th gear is used)
Driveline efficiency(TE): 82%, expressed in equation as 0.82 (assumes no synthetic lubricants)
Assumed Accessory Losses(Acc): 3,000 Watts (about 4 horsepower)
Note: The frontal area was estimated by taking the width and height of the car and multiplying by 0.8. This rough estimate of frontal area tends to be within about 5% of reality. The estimated driveline efficiency is typical for cars of that era, and the assumed accessory losses of 3 kW are a guess as to the average load being placed on the engine by the climate control, power steering, electronics, and other accessories at any given time, including the times that the accessories are demanding no load.
Knowing the tire size, this gives a wheel diameter of 24.7 inches, a wheel circumference of 77.6 inches, and 817 revolutions per mile(for the purposes of these calculations, will be expressed as 0.50766 revolutions per meter and denoted as T). This calculation was quickly obtained from the following tire size calculator:
http://www.miata.net/garage/tirecalc.html
The additional parameters that need to be expressed or calculated at various points to find the estimated fuel efficiency at various speeds are the following:
Velocity(V): expressed in meters per second
Force Air Drag(FD): expressed in Newtons
Force Rolling(FR): expressed in Newtons
Force Sliding(FS): sliding tire friction, expressed in Newtons, for a 1700 kg car, assumed as being 30 Newtons for simplicity’s sake
Wheel Power Required(WP): expressed in Watts
Engine Power Required(P): expressed in Watts
Air Density(Rho): 1.25 kg/m^3
Gravitational Constant(G): 9.8 N/kg
Engine Speed(RPM): expressed in revolutions per minute
Percentage thermal Efficiency(E): expressed in equations as a decimal
The equations we will use are the following:
FD = 0.5 * Rho * Cd * A * V^2
FR = G * Crr * M
WP = (FD + FR + FS) * V
P = WP / TE + Acc
RPM = V * T * 60 * R
To convert from miles per hour to meters per second, multiply the speed in mph by 0.44704.
So as not to lose anyone in confusion, I will model arceo_1’s car with the above baseline parameters at 70 mph. 70 mph is 31.3 m/s.
For FD, we get 462.7 Newtons. For FR, we get 183.3 Newtons. For WP, we get 21154 Watts. For P, we get 27798 Watts. For RPM, we discover that at 70 mph, the engine is turning at 2927 rpm.
The above paragraph tells use that the engine needs to put out 28.8 kW to maintain 70 mph, and is turning at 2927 rpm at that speed. Looking at the BSFC map posted in the thread that GREASYBEAST linked(post number 8), this tells us that our brake specific fuel consumption at that speed is about 310 g/kWh.
This means that 310 g/kWh of fuel is being consumed at 70 mph. A gallon of diesel fuel typically weighs 7.15 lbs(varies with temperature, but for purposes of the calculation, we will use 7.15 lbs), which is 3246 grams. There are 130500 BTUs of energy in a gallon of petro diesel, which is 38.2 kWh per gallon of petrodiesel. From this, we can calculate of percentage the fuel economy.
How?
At 70 mph, we will need to produce 28.8 kW from the engine for one hour to go 70 miles. We are consuming 0.0955 gallons of diesel fuel(310g/kWh divided by 3246 g/gallon) to generate 1 kWh of energy mechanically from the engine. To go 70 mph for one hour, or 70 miles, we need to generate 28.8 kWh from the engine. 0.0955 gallons/kWh * 28.8 kWh means we have used 2.7504 gallons of fuel to go 70 miles at 70 mph, or a fuel economy of 25.5 mpg!
25.5 mpg sounds pretty reasonable for a 300 SD at 70 mph, which is stock except for the tire size, don’t you think?
So what happens if we reduce the drag coefficient to 0.28 with some modest aerodynamic modifications(rear wheel skirts, smooth undertray, block off half of the grill, use a Kamm-style roof extension, lowered ground clearance to 4.5 inches), reduce the frontal area to 2.07 m^2 from the lowered ride height, swap in a 2.47 rear end, use synthetic lubricants to increase the efficiency of the driveline to 84%, and shave off 100 lbs of weight?
For FD, we get 356.6 Newtons. For FR, we get 178.4 Newtons. For WP, we get 17685 Watts. For P, we get 24053 Watts. At 70 mph, the engine is turning at 2355 rpm. This, 24 kW demanded at 2355 rpm, the BSFC map tells us that about 270 g/kWh is consumed. We have used exactly 2 gallons of fuel to do 70 mph for one hour, or 70 miles.
This is 35 mpg, right in line with the target by this topic’s creator!
BUT, there is much more than can be done with regard to aerodynamics and rolling resistance.
What happens if we not only keep the above proposed changes, but then reduce the drag coefficient further to 0.20 and reference area to 2.0 m^2 with some more extreme aerodynamic modifications(rear boat tail in place of Kamm roof extension, side skirts, cameras replacing side mirrors, front wheel spoilers, ect), reduce the frontal area to 2.0 m^2 from the mirror removal, and install Goodyear Assurance Fuel Max tires with a Crr of around 0.008 and size of 205/65R15 giving .492 revs per meter(there are much better tires for rolling resistance, some going as low as 0.006(!), but these are readily available for this wheel size and comparable in cost to normal tires and don’t sacrifice traction or tread wear characteristics)?
For FD, we get 244.9 Newtons. For FR, we get 129.7 Newtons. For WP, we get 12664 Watts. For P, we get 18076 Watts. At 70 mph, the engine is turning at 2282 rpm. This, 18 kW demanded at 2282 rpm, the BSFC map tells us that about 275 g/kWh is consumed. This is 1.531 gallons consumed to do 70 mph for 1 hour, which is 70 miles.
This equates to 45.7 mpg!
It is possible. Trust me, it is. Doing the work needed to get such a car to do this won’t be easy, but doable, yes. The C111-III streamliner would have had even better results thanks to its low weight, smaller frontal area, and taller final drive ratio.
Obviously, for WVO, B20, B100, and other alternative fuels, you are going to have to use a different energy amount per gallon to match the fuel used.
EPA cycle fuel economy will not be accurately reflected in the above calculations, although if you cruise down the interstate at a steady 70 mph, you probably will get similar results to those depicted here. These figures are for steady state cruising only. Math involving calculus is used when estimating fuel economy based on EPA driving cycles and it is probably above what most would be willing to go through on this board for a theoretical figure such as this.
I would also do my 300 SDL’s calculations in the exact same manner if I had a BSFC map for its specific engine; the link provided was for the OM617 engine, and not the one I have. The 300 SD engine is less efficient than the 6 cylinder used in my 300 SDL from what I have read on peachparts.com and elsewhere. I have done calculations for my 300 SDL(not posted) but without specific BSFC numbers; I am thus guessing in an educated manner. It is safe to say that my results will be at least as good as those projected with this 300 SD, if I can get the drag down to the appropriate levels.
Yes, 45 mpg *is* theoretically possible with this OM617 engine with the right modifications.
Whenever my 300 SDL’s body rusts away 15 years or more from now, I am probably going to use a VW chassis with custom low drag AND light weight fiberglass body for my engine, and gear the fucker for 200 mph. With say, 1,000 kg mass, 0.2 Cd, 1.4 m^2 frontal area, sticky racing tires with a Crr around 0.012, and 220 hp/290 lb-ft from engine mods, 60 MPG wouldn’t be out of the question, 0-60 mph in under 5 seconds would be doable, and somewhere around 190-200 mph top speed. Whether it would be stable at that speed, I would have to have a wind tunnel to have an idea beforehand... See the GM Precept(0.16 Cd, 2,600 lbs, 80 mpg, midsize car) on fuel economy, as such a figure of 70 mpg really isn't that far fetched.
Even if the engine from my 300 SDL is shoehorned into a Triumph Spitfire with no aerodynamic tweaks, the low frontal area, moderate drag coefficient(0.39 for Mk III, 1.4 m^2 frontal area, 1700 lbs laden weight with stock 350 lbs 4 cylinder engine), and being half the weight of a 300 SD would probably net 40+ mpg as well, and the thing would also haul some serious ass!
Another possibility would be using the engine and transmission from my 300 SDL on a 300 SL gullwing replica, just to keep it true to its Mercedes lineage. It would still be formidable in performance and fuel economy both, and it would definately have the pimp factor to attract the ladies.
(05-06-2010, 05:11 PM)The Toecutter Do you have available a BSFC map of the engine? If so, i'd love to have it so I can go through the math, to either support or deny my assertion.
![[Image: om617a-bsfc.jpg]](http://jason.pepas.com/images/om617a-bsfc.jpg)
Quote:Didn't the C111-III use a modified version of the OM617 engine? It still achieved more than 14 mpg at 195 mph, when the gasoline cars that can reach that speed and maintain it are hard-pressed to exceed 5 mpg at that speed(even with their engines at near-optimum thermal efficiency due to the load present). Given that the C111-III has about half of the drag of the typical "supercar", and a diesel engine that is about twice as efficient as an Otto Cycle engine, this varience in mpg makes sense.They ran the engine at its 2400rpm torque peak, while most gas engines peak torque in the 4000-6000rpm range. Thats sure to contribute to the difference. If they had used a wastegated turbo I'd bet its possible they could have run it lower. VNT conversions on the 617 usually peak right away on dyno tests, so if you match the turbo for maximum low-rpm efficiency through boost while sacrificing top-end power (a GT1748V for example) you should be able to run at 1800-2000rpm with enough torque to maintain speed.
ForcedInduction
05-07-2010, 07:37 AM
#35
(05-06-2010, 05:11 PM)The Toecutter Do you have available a BSFC map of the engine? If so, i'd love to have it so I can go through the math, to either support or deny my assertion.
Quote:Didn't the C111-III use a modified version of the OM617 engine? It still achieved more than 14 mpg at 195 mph, when the gasoline cars that can reach that speed and maintain it are hard-pressed to exceed 5 mpg at that speed(even with their engines at near-optimum thermal efficiency due to the load present). Given that the C111-III has about half of the drag of the typical "supercar", and a diesel engine that is about twice as efficient as an Otto Cycle engine, this varience in mpg makes sense.They ran the engine at its 2400rpm torque peak, while most gas engines peak torque in the 4000-6000rpm range. Thats sure to contribute to the difference. If they had used a wastegated turbo I'd bet its possible they could have run it lower. VNT conversions on the 617 usually peak right away on dyno tests, so if you match the turbo for maximum low-rpm efficiency through boost while sacrificing top-end power (a GT1748V for example) you should be able to run at 1800-2000rpm with enough torque to maintain speed.
(05-07-2010, 01:58 AM)The Toecutter [see above]
Most epic post of all time.
GREASY_BEAST
05-07-2010, 08:18 PM #36(05-07-2010, 01:58 AM)The Toecutter [see above]
Most epic post of all time.
(05-07-2010, 07:37 AM)ForcedInduction They ran the engine at its 2400rpm torque peak, while most gas engines peak torque in the 4000-6000rpm range. Thats sure to contribute to the difference. If they had used a wastegated turbo I'd bet its possible they could have run it lower. VNT conversions on the 617 usually peak right away on dyno tests, so if you match the turbo for maximum low-rpm efficiency through boost while sacrificing top-end power (a GT1748V for example) you should be able to run at 1800-2000rpm with enough torque to maintain speed.
I'll have to keep that in mind. Thanks. Perhaps I shouldn't aim for only 45 mpg, but maybe into the 50s... I have very little experience playing with turbos, but I will accumulate some gladly! My concern with my 300 SDL is finding the tallest gear ratio that will fit; putting on a different turbo to further exploit its lower RPM at cruising speed would be the proverbial icing on the cake, and may yield some dramatic results for fuel economy.
Does anyone here have any fuel economy datapoints to share on trying different turbos with the same engine?
I do prefer to have a high amount of torque and low revs, versus the opposite often found in hotrodded Hondas, just so I can bait unsuspecting cars on the highway! When my turbo was functionig properly, even though I only had ~150 brake horsepower on tap, the torque and the gearing this car posessed stock had allowed it to accelerate very readily once it had built up some speed; 0-60 may have been a sedate 11 seconds or so, 0-30 was outright embarassing, but from 50-80, it could match some 200 horsepower cars of similar weight... I love it. Imagine what a turbo set up to exploit this car's powerband would do... there may be a possibility of having a 220 horsepower 300 SDL, that at least on the highway, can hang with some 300 horsepower gas burners. The drag reduction would also help with this once implemented since more torque is left over to accelerate the car than to push away air...
The Toecutter
05-08-2010, 01:41 AM #37(05-07-2010, 07:37 AM)ForcedInduction They ran the engine at its 2400rpm torque peak, while most gas engines peak torque in the 4000-6000rpm range. Thats sure to contribute to the difference. If they had used a wastegated turbo I'd bet its possible they could have run it lower. VNT conversions on the 617 usually peak right away on dyno tests, so if you match the turbo for maximum low-rpm efficiency through boost while sacrificing top-end power (a GT1748V for example) you should be able to run at 1800-2000rpm with enough torque to maintain speed.
I'll have to keep that in mind. Thanks. Perhaps I shouldn't aim for only 45 mpg, but maybe into the 50s... I have very little experience playing with turbos, but I will accumulate some gladly! My concern with my 300 SDL is finding the tallest gear ratio that will fit; putting on a different turbo to further exploit its lower RPM at cruising speed would be the proverbial icing on the cake, and may yield some dramatic results for fuel economy.
Does anyone here have any fuel economy datapoints to share on trying different turbos with the same engine?
I do prefer to have a high amount of torque and low revs, versus the opposite often found in hotrodded Hondas, just so I can bait unsuspecting cars on the highway! When my turbo was functionig properly, even though I only had ~150 brake horsepower on tap, the torque and the gearing this car posessed stock had allowed it to accelerate very readily once it had built up some speed; 0-60 may have been a sedate 11 seconds or so, 0-30 was outright embarassing, but from 50-80, it could match some 200 horsepower cars of similar weight... I love it. Imagine what a turbo set up to exploit this car's powerband would do... there may be a possibility of having a 220 horsepower 300 SDL, that at least on the highway, can hang with some 300 horsepower gas burners. The drag reduction would also help with this once implemented since more torque is left over to accelerate the car than to push away air...
(05-05-2010, 09:06 AM)meareweird Beautiful car!!
thanks. I'd also like to keep it that way. Im not willing to give to much up on the looks.
im thinking i need to find a way of getting some vortex generators (ala evo) or maybe roof spolier...im not turning my whip into a nerd mobile...or a small spoiler (M5ish)
I think smoothing out the underside is going to be my main focus...5 bucks I can get it like this...
Ron Burgundy
1982 300SD - 310,XXX - Orient Red
(05-05-2010, 09:06 AM)meareweird Beautiful car!!
thanks. I'd also like to keep it that way. Im not willing to give to much up on the looks.
im thinking i need to find a way of getting some vortex generators (ala evo) or maybe roof spolier...im not turning my whip into a nerd mobile...or a small spoiler (M5ish)
I think smoothing out the underside is going to be my main focus...5 bucks I can get it like this...
Ron Burgundy
1982 300SD - 310,XXX - Orient Red
(05-08-2010, 01:44 AM)arceo_1(05-05-2010, 09:06 AM)meareweird Beautiful car!!
thanks.
im thinking i need to find a way of getting some vortex generators (ala evo) or maybe roof spolier...im not turning my whip into a nerd mobile
Vortex generators have such a small effect on drag that you will need a wind tunnel to tell the difference. They may reduce your drag coefficient by abouit 0.001-0.002, but probably no more...
A roof spoiler, especially a Kamm-style one, would help greatly. So would a smooth undertray which isn't visible to the casual observer. A partial grill block would also not be noticable. Those three items by themselves could have a > 10% impact on your fuel economy, and may get you a Cd of around 0.30(guess, based on other cars I have seen).
With this engine after studying the BSFC chart, it seems a swapped out final drive ratio would have a bigger impact than I thought it would before having ever seen that curve; then again, most of my studies on this have pertained to gasoline cars.
You could probably meet or come close to your 35 mpg goal without significantly altering your cars looks. If you want more, it's nerdmobile time...
***edit***
Also, that is basjoos Civic that you posted. If some fiberglass work were done to make it look like it was built that way from the factory, it would look decent. As it is, the car is his testbed. I would not permanently keep my SDL looking like that if I did similar mods. I would want it to look professional. Needless to say, you can't argue with 90 mpg at 55 mph, 40 mpg at 90 mph, and 70 mpg in normal highway driving... That thing is a money saver.
The boattail he designed for that Civic is a thing of beauty when it comes to function. A member of ecomodder.com made one for his Pontiac Firefly(Geo Metro in US), and by itself it added 15% to his highway fuel economy. A Kamm style roof spoiler won't be nearly as dramatic, and vortex generaters wouldn't even give you a measurable fuel economy benefit by themselves, *but* every little bit helps, and a bunch of small modifications do eventually add up to something significant.
The Toecutter
05-08-2010, 02:00 AM #39(05-08-2010, 01:44 AM)arceo_1(05-05-2010, 09:06 AM)meareweird Beautiful car!!
thanks.
im thinking i need to find a way of getting some vortex generators (ala evo) or maybe roof spolier...im not turning my whip into a nerd mobile
Vortex generators have such a small effect on drag that you will need a wind tunnel to tell the difference. They may reduce your drag coefficient by abouit 0.001-0.002, but probably no more...
A roof spoiler, especially a Kamm-style one, would help greatly. So would a smooth undertray which isn't visible to the casual observer. A partial grill block would also not be noticable. Those three items by themselves could have a > 10% impact on your fuel economy, and may get you a Cd of around 0.30(guess, based on other cars I have seen).
With this engine after studying the BSFC chart, it seems a swapped out final drive ratio would have a bigger impact than I thought it would before having ever seen that curve; then again, most of my studies on this have pertained to gasoline cars.
You could probably meet or come close to your 35 mpg goal without significantly altering your cars looks. If you want more, it's nerdmobile time...
***edit***
Also, that is basjoos Civic that you posted. If some fiberglass work were done to make it look like it was built that way from the factory, it would look decent. As it is, the car is his testbed. I would not permanently keep my SDL looking like that if I did similar mods. I would want it to look professional. Needless to say, you can't argue with 90 mpg at 55 mph, 40 mpg at 90 mph, and 70 mpg in normal highway driving... That thing is a money saver.
The boattail he designed for that Civic is a thing of beauty when it comes to function. A member of ecomodder.com made one for his Pontiac Firefly(Geo Metro in US), and by itself it added 15% to his highway fuel economy. A Kamm style roof spoiler won't be nearly as dramatic, and vortex generaters wouldn't even give you a measurable fuel economy benefit by themselves, *but* every little bit helps, and a bunch of small modifications do eventually add up to something significant.
82 300SD aka The Flyin Pumpkin (Gone): 7.5mm super M-pump, T3 60 trim turbo, Coldish air intake, A/W intercooler, propane injection, SW Boost and EGT gauges, Monark 265 nozzles, ported/polished cylinder head.
84 Euro 300D 4 sp: White with black trunk and hood. Blue cloth interior. Manual everything. 300DT front swaybar. C320 17" wheels. Now with the Flyin Pumpkins engine!
arceo_1, any updates on progress or milage?
82 300SD aka The Flyin Pumpkin (Gone): 7.5mm super M-pump, T3 60 trim turbo, Coldish air intake, A/W intercooler, propane injection, SW Boost and EGT gauges, Monark 265 nozzles, ported/polished cylinder head.
84 Euro 300D 4 sp: White with black trunk and hood. Blue cloth interior. Manual everything. 300DT front swaybar. C320 17" wheels. Now with the Flyin Pumpkins engine!
(05-20-2010, 10:47 AM)Biohazard arceo_1, any updates on progress or milage?
nothing new so far. last fill up got me 31.3 MPG.
It's getting hot in AZ, so the A/C gets turned on now...we'll see what that does.
Ron Burgundy
1982 300SD - 310,XXX - Orient Red
82 300SD aka The Flyin Pumpkin (Gone): 7.5mm super M-pump, T3 60 trim turbo, Coldish air intake, A/W intercooler, propane injection, SW Boost and EGT gauges, Monark 265 nozzles, ported/polished cylinder head.
84 Euro 300D 4 sp: White with black trunk and hood. Blue cloth interior. Manual everything. 300DT front swaybar. C320 17" wheels. Now with the Flyin Pumpkins engine!
Thats not all bad! Is that mostly highway or combination of city/highway? I'm usually around 26ish for a tankfull, thats combined city and highway though. The a/c will probably drop it a little. Mine crapped out so it got removed. Then again, I'm not in Arizona with triple digit temps...
82 300SD aka The Flyin Pumpkin (Gone): 7.5mm super M-pump, T3 60 trim turbo, Coldish air intake, A/W intercooler, propane injection, SW Boost and EGT gauges, Monark 265 nozzles, ported/polished cylinder head.
84 Euro 300D 4 sp: White with black trunk and hood. Blue cloth interior. Manual everything. 300DT front swaybar. C320 17" wheels. Now with the Flyin Pumpkins engine!
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