I'm curious about these...my use for one would be for a medium sized RV for musical touring purposes. I'm going diesel only because WVO will be a huge component of making ends meet on the road, and because there's no gas motor that can both move a load like that and deliver the fuel economy I'm after.

Previously I'd been looking at utilizing a 5.9l Cummins and an Allison. I know for a fact that one of those will move a vehicle as large and heavy as a 1970 GMC Bus over the rockies despite a dying turbo and a slipping transmission - LA to NOLA to West Virginia to Monterey, both times going over the Vail pass. The turbo and transmission were eventually rebuilt and as far as I know that thing is still humming down the highway. I was duly impressed, especially since we were seeing mpg #s higher than 12 on the flats despite all of our handicaps.

I'm thinking of something less heavy than that, and while the Cummins is still a great choice I'm wondering about these NPR diesels. 3.9l, 140hp with an intercooler if I remember correctly but something more like 350lb-ft. I was on one guy's site offering parts for NPR conversions and he claimed that a full size Ford van pulled a travel trailer (Airstream, I'm thinking) running this motor and got 22mpg highway despite being bolted to an inefficient, non-overdrive C6 transmission. That sounds like something I can get down with, but I'd want to verify such numbers in the stock NPRs first (people claim a LOT of things on the net, after all).

If anyone wants to chime in with some NPR experience, I'm all ears. Seems for the same amount of money you could get a Dodge 3500 or a NPR Box Truck...of course, the advantage of the Cummins being that, of course, more power is available if the need arises...I don't know of anyone modifying NPR motors but technically, of course it could be done.

http://www.4btswaps.com
There's an Isuzu forum there dedicated to these engines (4BD1T). I'm a mod.

I've got one of these and had it for a long time in my 4wd. Some of our members are hell bent on finding the limits of the engines and haven't broken much yet. Apparently the stock head gasket starts to leak at 60psi boost.

No kidding. Good heads up there. Hey, since you have one, and you're on this forum...well, let's see if you can guess where I'm heading with this ;-)