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US27inKS has it right.
In addition, turbo and non turbo diesels usually run with the same compression ratio. For instance, the Perkins M65 was 17.5:1; the M85T was the same engine turbocharged and was 17.5:1, and so on.
I think you'll find other than the manifolds and fuel pump calibration, they're the same engine.
You can turbocharge (or supercharge) a diesel without adding an aftercooler. By cooling the compressed intake air, you can stuff more oxygen into the cylinders, which can then burn more fuel and produce more power than with just the turbo.
Supercharging requires power off the crankshaft to compress the intake air. Turbocharging works off the heat in the exhaust, so it compresses the intake air for 'free'. (Supercharging doesn't have any turbo lag, which is why it's used on cars.)
The benefit of supercharging is to put more air into the engine, which allows you to use more fuel and produce more power. It doesn't improve the efficiency of the engine. In fact, the power to drive the prop will still be the same, but the engine will probably burn more fuel to go the same distance. After all, it's going to take engine power to run the supercharger, and the extra air pumped into the engine is just going to be pumped out the exhaust.
Tim
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