I'm sure mufflers, emissions controls, water pumps, alternators and such added help drop power. (That is if this stuff wasn't there, I suspect some of it wasn't on the test stand)
The rest probably comes from the Forderization of the process to mass produce the engine. Tolerances aren't as good on the mass produced engine vs the hand built prototype.
Perhaps the 250HP was because the prototype could spin to a much higher RPM than the production cars, since HP is related to both torque and RPM.
Didn't get the chance to ask about that one. But I suspect the Porsche prototype could spin faster than 7K RPM
Combine that with better breathing and now emissions, and I could easily see 250HP.
TB
Just speculating, in the absence of facts.
