I am thinking of adding a turbo to my unimog to help driveability issues, I figure I might be able to get some help here, the theory is the same.

A 5.6L inline 6 diesel mercedes om352 engine is naturally aspirated and makes about110 peak horsepower at 2800rpm. The pump can be turned up for a bit more power and the governor adjusted for more RPM, but it will raise the EGT too much for what I need, and EGT gauge is mandatory as it will run close to 1350 fahrenheit. Originally it did 75kms with stock engine at maxed at 2500rpm, new engine is governed for 2800 rpm, can do 85km/h. I have new tires for it, the larger tires installed will also rob more power, which this 8000 pound truck cannot afford but will increase my top speed to a theorethical 99km/hr, more if I up the governor and pump. For prolonger full power use like driving on the highway, adding a turbo will add more air and lower the EGT if I understand correctly.

How much boost could a diesel engine take before more fuel is needed? Is it like a gas engine, where after x-amount of boost the air mixture is too lean and would get hot again? Is there a "happy zone", boost that a diesel engine would like? I know some of the dodge cummins engines run crazy boost to make serious horsepower, I dont want to go that crazy, I'm strictly interested in prolonged high rpm use, the drivetrain cannot take more than 200 hp without a lot of work

 

Welcome to the DTR.

Diesel engines are not bound to the same air fuel ratios as a gasoline engine. More air and leaner combustion creates cooler combustion temperatures, so any boost you can add to the engine would greatly improve its performance as well as keeping the EGT's down.

Sizing the turbo wouldn't be that difficult, "adding" the turbo, may be another story as far as plumbing. However, being that it is Mercedes there is a good possibility that there are turbo flange type exhaust manifolds available that would fit the engine without much modification. The air side of the turbo would not be hard and for the fuel you are using, probably not in need of intercooling either. I am thinking a steady 14-16 psi boost at peak RPM would be ample and therefore the intake air temps wouldn't be totally out of the useable range.

Funny you post this, I was just behind one of these bad boys in Grande Prairie last week and that thing was ripping in town. Didn't know it had a top speed limit though.....

 

since a NA diesel normally has a higher compression ratio than a turbocharged diesel i wonder how much boost you could safely add without blowing the heads off. assuming the engine in question has a very high C/R

 

The compression ratio should be around 17.1:1. There are diesel versions but be sissy is model never came with a turbo it will be a PITA to make it fit. I am doing a 2 inch cab lift which will give more room to work with. I need the turbo about 10 to 15 inches lower then the exhaust manifold because there just is no room for it, needs t go under the cab. If I put a snorkle type intake behind the cabin a lot of my plumbing will be easier. I was thinking of one of those air filte assemblies I see behind the cab on the hino cabover trucks. The turbo version of the newer engines do come with piston cooling jets but mine does not, limiting how much power I can make, some or these engines make 240 hp wih a turbo from the factory. I don't know what other internal differences there are

 

I've added turbos to two of my John Deere tractors.
JD recommended 15 psi boost at full throttle.
The guys here set me up with the correct turbos> http://www.htturbo.com/

 

may also want to try 4btswaps . com

 

Having the turbo remote mounted is not the end of the world and if it makes the install easier, then go for it.. Keep in mind oil flow and feed to/from the turbo for good cooling and long life. The trick would be to wrap the exhaust to the turbo from the engine to maximize the heat energy to the turbo.

The compression ratios on Diesels don't differ much from NA to turbo versions. 17.5 to 1 would be ideal for the application. Some earlier IDI GM diesels had 18 to 21:1 compression.

For the power you are wanting to gain, I don't think the fuel you have will be an issue to need the cooling jets on the pistons. The fuel pump will not have the ability to up the fuel with respect to any positive pressure. There probably is not any AFC to work with as its all screws to adjust fuel to the RPM range without any provisions for boost control. Just adding the turbo to the engine at this point will help in achieving a little better power and cooler operation.

 

How long will a turbo last if it is putting out 15 psi boost all the time? I never had a turbo diesel vehicle but I just can't see it running all the time. I know my turbo 4 banger cars it comes and goes as needed. Would an adjustable wastegate help improve life, say 5 psi for highway cruising and 15 in the city?

They way I was told is that a turbo turns all he time in a diesel engine, even at idle. Is there perhaps a thrrottle actuated valve to control he wastegate, or a turbo will live for hundred thousand mile at full boost all the time and I shouldn't worry?

 

I wouldn't worry about the full time boost numbers or wastegates. The engine will make boost depending on the fuel you give it. So even at peak RPM if the load is low, you probably would only make about 3-4 psi boost, which really is nothing, but will significantly improve your EGT's and overall soot output.

As long as there is exhaust, the turbine turns, no mater what application you use the turbo for. They are designed to run in their map (pressure and speed range) for life, probably around 10-15,000 hours with good clean oil supply. Its when guys put the turbo outside the pressure range or have excessive temperatures that they die. Industrial engines run at 12-15 psi boost 24/7 for a good couple years on a stock turbo.

If you size the turbo to provide the maximum boost at your maximum load and RPM, the rest should take care if itself. Wastegating is getting into performance where you want the turbo to provide maximum boost sooner in the RPM range (ie smaller turbine flow area) and still have the ability to reach maximum RPM/load on the engine without going over the maximum boost pressure required.

 

http://www.youtube.com/watch?v=_Vmwb...yer_detailpage

Unimogs are amazing- that is a nice looking truck you have there.