This one is only semi-Mercedes related...

I recently bought a low-mileage good running GM 4.3 L V6 diesel engine out of a FWD 84 Olds Cutlass for a couple of hundred bucks. THIS IS NOT one of the converted gasser V8s that GM had such disastrous problems with. It has 14 head bolts per head and is built appropriately beefy for a diesel. Almost all reports are that this is a very good motor, but it was just introduced at the wrong time - right after several years of the GM V8 diesels being out there on the road and failing miserably. By the time the V6 was engineered, produced, and introduced, the public had such a bad taste in their mouth for the GM diesels that nobody wanted one and the 4.3 L was discontinued after only 3 years.

Anyway, this particular motor mates up to the same trannies as the GM 2.8 L V6 gassers. It just so happens that at about that same time, Jeep introduced the Cherokee - and the first ones on the market had either the GM 2.8 L V6 gasser (putting out 115 HP and 150 ft-lbs torque), OR a 2.1 L Renault turbo diesel (producing 85 HP and 132 ft-lbs torque). Both of these engines mated up to the same AX5 5-speed manual, and the 2.8 L was also offered with the A904 automatic. For some reason they never offered the automatic behind the diesel - even though it would obviously handle anything the little Renault mill could dish out.

Well, enough history - fast forward to the present day. I recently made another aquisition - a 1986 Jeep Cherokee with an A904 automatic tranny and a 2.8 L V6 that has one rod sticking out the side of the block (!) for the princely sum of $100. So now you can see where I'm going with this. I'm getting ready to transplant the 4.3 diesel into the Cherokee. It should almost drop right in with very little trouble.

In stock trim the 4.3 only makes 85 HP - the same as the Renault turbo diesel - but it pumps out a respectable 165 ft-lbs torque - more than either the 2.1 L turbo diesel OR the 2.8 L gasser. Here's where the story takes a turn towards the Mercedes marquee - and where I start asking questions...

I have a spare turbo setup from an OM617 and I'd like to graft it onto the 4.3 L V6. Since it was installed in a FWD car, GM, in their infinte engineering wisdom decided not to run dual exhausts. Instead they chose to make the 2" downpipe from one exhaust manifold cross under the engine, connect to the other exhaust manifold, and then all of the exhaust from both banks exits that manifold through a larger 2.5" pipe. It is almost as if they planned to add a turbo to this engine right from the start.

Here are my thoughts, and I'm hoping the turbo gurus around here can either tell me I'm on the right track, or tell me where I'm going wrong. On the 3.0 L OM617, the stock turbo maxes out at around 14-15 PSI. So if it were on a 4.3 L (based on the volume of air being taken in), with roughly 1.4 times the displacement, the turbo compressor ought to be able to supply enough volume to make about 2/3 that much pressure - something like 9 or 10 PSI max. Conversely, since the volume of exhaust gasses being pushed out through the turbo impeller is 1.4 times greater, the turbo should also get enough flow to start to spool up at about 70% of the RPMs that it takes to spool it on the 3.0 L (the inverse of 1.4 = .71 or 71%). Assuming it works that way, the turbo would start to spool below 800 RPMs - almost at idle, and would spool up to its wastegated max pressure really quick.

I'm thinking that if the wastegate can be adjusted to limit boost pressure to around 7-10 PSI, then dumping the excess exhaust through the wastegate will also keep the turbo from being too big of a restriction on the exhaust flow (creating excessive backpressure) and keep the turbo from over-speeding.

My goal here is to bump the HP output of the 4.3 L to at least the same HP output as the 2.8 L gasser, and of course the torque would increase proportionally. If I can get it up to 115, maybe even a little higher (130HP and 250 ft-lbs torque would be AWESOME!) I'd be one happy camper. I figure that if by adding a turbo Renault could get the same HP out of the little 2.1 L diesel (with half the displacement) as what GM got out of the NA 4.3 L, then it doesn't seem unreasonable to expect that adding a mild turbo boost (and turning up the fuel delivery of course) on the 4.3 L ought to be able to bump up its output something like 40%-50%. If it works out that way, this ought to be a really cool project.

Trouble is, I'm not that well versed in turbos, so I'm not sure it will all work this way. It seems logical, but I just don't know for sure, so...
CALLING ALL turbo gurus! Please let me know what you think about the idea and my thought processes here...

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1984 300 Coupe TurboDiesel
Silver blue paint over navy blue interior
2nd owner & 2nd engine in an otherwise
99% original unmolested car
~210k miles on the clock

1986 Ford F250 4x4 Supercab
Charcoal & blue two tone paint over burgundy interior
Banks turbo, DRW, ZF-5 & SMF conversion
152k on the clock - actual mileage unknown