Engine Discussion: Various definitions of HP, 2.7 vs. 3.2?
 

Hello Pelicans,

I was reading that terrific series of articles in Classic Motorsports Magazine that talks about the 1973 Carrera RS. The article says the Carrera RS had a 2.7 liter engine that produced 200 SAE net horsepower.

First discussion topic: What do the various ratings of horsepower mean? I have seen: SAE, DIN, RWHP, BHP and a few others.

Second discussion topic: How is it that the 2.7 engine produces 200hp, and the 3.2 liter engine produces 207 hp? The 2.7 was said to be a compression ratio of 8.5.1 and the 3.2 is 9.5.1, and the Euro model 3.2 was 10.?.1 producing 231hp. Why doesn't the 3.2 Carrera, bigger motor with higher compression ratio put out much more than the 2.7?

Camshaft timing and overlap, rsulting in very different torque curves for one.

The RS has S cams which make peak power at higher revs.

The area under the curve greatly favors the 3.2.

SAE net is ~~= to DIN hp.

SAE gross is a lot higher.

The difference lies primarily in the test conditions - what accessories are required to be connected to the motor when yo measure hp.

RW hp = hp measured at the rear wheels. This will be lower b/c of frictional losses in the gearbox, etc. and tire squirm and so forth. To compare engines, you need an engine dyno not a so-called "road" dyno. The latter measure RW hp.

These are not really 'discussion' topics. They are merely definitions.