Other answers in blue.My plan for this engine was to cruise it at around 200hp and use 300hp for occasional use.
What RPM's does the Duramax engine run to get 200 and 300m HP respectively, that is where you need to peg the throttle and propeller.
Don't forget that for every 2,343 feet of elevation you will loose 1psi of pressure, which will effect your boost pressure internally.
I think you must be talking about a different engine than I am because others have said the Duramax weighs around 800lb (post 14),
I agree, but you asked about the weight of a Cummins motor, i know that duramax engines weight about 800lbs, the old 7.3L Powerstroke weight 746lbs its self.
The Cummins is a overbuilt motor and that is why it weight so much, plus its a fully blown iron block, while the duramax, and powerstroke engines use aluminum blocks and aluminum heads.
and can put out 600hp absolutely stock with only the addition of an aftermarket chip. I find it difficult to believe your claim that one will only cruise at around 80hp.
I was explaining how i drive down the highway with probably 80 or 100 HP. Plus, your not driving down the road running full boost and full RPM's.
Without a load on the motor your fuel consumption is non existent, and so is your horsepower production. Diesels only make power when a load is placed on them. They HP production has only to deal with what is needed to keep the vehicle moving.
If you want to run on 200 HP you need to modify or chip the motor to produce 200HP at the RPM and the boost level you expect.
For Example i run down the Parkway running about 1,400 rpm's, (without the turbo boosting that is about 80 HP, but if i go up a hill the turbo will spool up and increase the boost and HP to about 120HP) even under acceleration at 2,200rpm's my truck is only producing180HP. (BTW i got that dyno graph from the Dodge website for my model year truck).
But you run full boost to keep the truck going once your up to speed. So you don't need all 120hp to keep the truck going. This is where things get different because you will have to run full boost the whole time your airplane is in the air, there is no rolling values, and no coasting in the air.
So you will have a load on the motor, and the turbo will spool up as necessary to produce enough power to keep the airplane/truck moving at speed. As long as your spooling.
Diesels only make power under load, You are not making 360HP at 2,000 RPM, running 1psi of boost.
ALso anticipate boost loss as you go up in altitude.
In any case, I will not modify a car or truck engine internally to run in an airplane, only remove all possible emission components and switch to carburetor if it's a gas engine. I will not invest in a reduction gear, even for a gas engine. (except possibly in an ultralight)
I should also mention that rpm's don't necessary negate to HP with a diesel. You can run 3,000 rpm's and produce very little Horsepower.
But as long as your not loading the diesel you also will not get any heat production or horsepower gain, simply because unlike a gas motor if you raise the rpm's up your mostly free wheeling off the motors ability to self ignite.
For example, in the winter i can High idle my truck at 1,200RPM's all day long and not see the engine coolant warm up for anything, But switching to 3 cylinder High idle will put a load on the motor about 17% to be exact, that means the engine will warm up. With EB on and 3 cylinder high idle i can load up to 30% on the motor.
Conversely, on 6 cylinder high idle, with 0-1% load i'll burn about 1 gallon an hour. but on 3 cylinder high idle i'll burn 2-2.5GPH, and with my Exhaust break on with 3 cylinder high idle a whopping 4.5GPH.
This is all at 1,200RPM's, but as you can see the gallon usage went up considerably, as i increased the load on the motor.
diesels are a different animal from gassers.