Thread: supercharged 300tdi ?

Last I heard it was running pretty good....I'll see if I can get an update for you....

I had considered this last week, an sc-14 compounded into the standard 300tdi turbo.

Originally Posted by kreecha

I had considered this last week, an sc-14 compounded into the standard 300tdi turbo.

Twin-charge (turbo and SC) normally needs to work the other way. If you want the turbo to suck through the SC you need a bypass valve as the SC can't flow more air as the turbo starts to work.

To put turbo and SC charger power into perspective:
A stock 300tdi turbo requires ~14kw shaft power for the engine to produce it's 82kw. This results in about a 12kw pumping loss.
A supercharger (lower efficiency compressor) to produce the same boost and flow would suck around 18kw directly from the crank. You are 6kw worse off.

A better turbo (TD5 GT2052 for example) would have a pumping loss of only 6kw. Leaving you ~6kw better than the original turbo and ~12kw better than the SC.

But that's only at 4000rpm max power.

Consider 2000rpm max torque. Putting out ~12psi boost for ~6kw shaft power.
The stock turbo is producing more boost than back pressure. It only takes 3.4kw from the engine to produce 6kw of shaft power.
A SC would require around 7kw of shaft power and take this directly from the engine. You would be 9.6kw worse off at 2000rpm with a supercharger. Quite a problem when it only produces 55kw at 2000rpm.

Then if you want to cruise at 2000rpm the turbo scales right down to only meet demand. But the supercharger can't.
Your supercharger continues to whine away taking the same 7kw of shaft power and slaughtering your fuel economy.

Which is why there are exactly zero manufacturers making supercharged road diesels.
High fuel consumption.
Low power and torque.
High noise.
Can't scale the output to match the demand.