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OM606 compound small turbo size
engineengineer Offline
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#1
OM606 compound small turbo size
Hi all, planning an OM606 compound build, with the aim of daily driveability while keeping top end power. I see many people have built compound setups, usually using an HX35 as the small turbo and HX40/50/55 as the larger turbo. I am considering a smaller turbo, perhaps an HX30 or HX27 for a much lower boost threshold. 
Can anybody give me an idea of what RPM I can expect to see usable boost with an HX30 or HX27 compared to an HX35? Also, would the HX30/27 compressor housing be too restrictive up high? 

The alternative is to supercharge and single turbo. Has anybody had good results with the like of a big Eaton? Or would you expect this to increase fuel consumption on the highway greatly?


Thanks, Jack.
(This post was last modified: 01-20-2019, 09:09 PM by engineengineer.)
01-20-2019, 08:43 PM
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Turbo Offline
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#2
RE: OM606 compound small turbo size
I have original R2S turbo compound turbo
small is like original turbo on om606 but can boost a lot more, LP turbo will go to something like 400whp, it will boost 3 bar if you want
they are like 25kg together.
what are you going to put it in for a car?
mercedes s210 will have something like 10-20mm spare place but exhaust need to be lite bit special and turbo need to be rotate and make LP on top instead of original HP top with is possible with a little trix
very easy to control, no turbine or compressor bypass needed
PM me if you want to know more

There is a lot to think about if you want to built a well working compound set up, you just not put is as simple like -"Can anybody give me an idea of what RPM I can expect to see usable boost with an HX30 or HX27 compared to an HX35?"
play with match bot and you will learn a lot, Holsets exhaust house can ruffly translate into A/R and it can also be translated into exhaust swallowing on the turbine side just to give a hint

I have been thinking of writing a ABC on how to calculate turbo but no time so fare for it
01-21-2019, 03:00 PM
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firen456 Offline
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#3
RE: OM606 compound small turbo size
Been building a compound setup for a while. Started my calculations with a KKK K29 on PR 2-2.5 at about 60-65lb/min. If figured out that a HX30 with a PR 2-2.5 at about 32lb/minwould work out wel. Will run that setup in spring and can sa more...
01-22-2019, 03:15 AM
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Turbo Offline
Holset
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#4
RE: OM606 compound small turbo size
firen456 can you please in detail explain your calculation of the turbos.
Just to be clear a compound means that both turbos work together at all time, this you do for really high boost
then there is sequential turbo set up where one turbo starts and the other turbo eventually take over all work needed
this you must take in consideration in the calculation.
intercooler, between turbos, make difference in the choosing process

First what you want to achieve with the setup , target parameters? I want that boost at that rpm to be able to make that power from the engine.....
01-22-2019, 05:14 AM
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firen456 Offline
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#5
RE: OM606 compound small turbo size
reason for compounding is to stay in the efficient area of the comp map. It's difficult to find a large turbo providing over 60lb/min at 3bar boost with high efficiency. Second, this turbo will have some huge lag. The pressure ratios of the turbos are multiplied in a compound setup. In a real compound setup it's not neccessary to bypass the hp turbo. If u would do this, the smapper hp turbo would only be kind of boost assistance but the problem of working in an inefficient area of the lp compressor will stay... Let's say you build up about 1bar boost with the lp, it must have a pressure ratio of about 2.0. Then you will let the hp turbo also work in a pr of 2.0. PRs will be multiplicated and so u got pr 4.0 which means around 3bar boost, depending on some losses and compressor efficiency. There are many diesel compound calculators around. Just calculate the air demand of u'r engine and find a proper LP turbo. Then calculate the needed flow of the hp turbo. The pr of it do u know from the desired boost level u wanna run. After that find the right hp compressor whichs works efficient around this pr and flow. 

I wanna run around 3bar boost, maybe a little more with as little epg as possible. Problem on compound setups seem to be egp. The balance of pr between hp und lp turbo will have to be chosen properly so that egp stays low.
01-22-2019, 07:07 AM
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atypicalguy Offline
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#6
RE: OM606 compound small turbo size
There are many reasons to compound. Even the R2S setup used by Turbo came in varying configurations for different vehicles. Some required full compound for higher boost, some required earlier spool and were more sequential in operation. Running on the map of whatever turbos you are using is always smart of course. But you might choose to have the small turbo doing nothing at high rpm/horsepower, or you might choose to have it always in the mix.

So the desired power level and driving characteristics of the vehicle drive the turbo selection and function. Some may want good low end toque at low rpm. Some may care less about this.

For an OM606 to run higher hp ~400 at an AFR of 17:1, and not need 4 bar of boost to hit the air mass target, you will need an hx50 sized turbo. Personally I favor the hx52 "pro" model. It can supply the needed airflow at a moderate PR. Anything smaller will be boosting 4 bar at 80lb/minute, which is not what you really want in a compound. If you want 300hp then an hx40 will do the trick. The 40-sized turbos will make big power at lower AFR, but EGT will be high and they will smoke a lot before they come on line. Outfits like DPUK don't care about that stuff; they maintain the duty cycle is so low that the EGT doesn't matter, and they don't even tell you what it is when they sell you a kit. It is true that most street cars cannot put out maximum power for longer than a few seconds before breaking all sorts of laws and common sense.

But if you want earlier spool, little smoke, and good pull from low rpm, you need a vnt or compound. If compound, you can still use vnt, but not necessary. If not VNT, small turbo must be small to spool early.

Smaller turbo can be truly tiny. he221w, hx30 40mm/6cm, or even a stock om648 vnt Garrett. I would be tempted to try an he200wg 5cm, but it would only wake the big turbo and then go to sleep instantly. It might not spool an hx50 either. You can easily work this out in a spreadsheet taking into consideration compressor and intercooler efficiencies, and then plan the whole system and how much boost you need from the little turbo to light the large one.

You will need large bypass gates, one or two 60mm to keep backpressure down.

If you want to run full compound at all rpms, then you need a larger HP turbo. I think Sultzi had a nice 9cm HP turbine housing on a daily compound driver, so look up that build thread.
01-27-2019, 04:45 PM
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barrote Offline
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#7
RE: OM606 compound small turbo size
We assume u have practical experience ?
With diesels?
FD,
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01-28-2019, 02:54 AM
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