84_Carrera

Yep, I usually estimate about 15% for a std 5-speed FWD, 17% for a FWD w/ LSD or RWD 5-speed, 22-25% for an automatic (FWD / RWD) when guesstimating crank numbers from wheel numbers. That's a tad high given today's electric fans, etc., but is pretty close from what I've found at the dyno.

FYI, here's the dyno on mine after I bought her, no changes from purchase.

wholberg

Here is a link to a page at 911chips.com, http://www.911chips.com/ignition.htm, that discussed this very issue. According to Steve Wong, in 87 Euro cars were 231HP, Non-CA U.S. cars were 217HP, and CA-only cars were 200HP due to additional timing retardation.

ked

I recall reading (sorry, can't find it at the moment) that the 911 design, having no driveshaft (ie from front engine to rear differential), yields less transfer loss than any other layout - on the order of 10%. If so, yet another example of Ferry's ingenious approach to powertrain systems efficiency.

84_Carrera

I find 10% a little hard to swallow on an across the board statement. If the non-driveshaft was the only issue, nearly all FWD cars would have similar losses, and they typically run around 15% from what I've been told & experienced. Although, 10% losses would mean I'm running around 224 crank horses instead of 240, which is a lot easier to see from a chip.

ked

FWD systems usually have intermediate shafts to achieve compactness, some designs are extremely (mechanically) inefficient in order to achieve ease-of-production. Again, we need an expert (Pete, Steve?) to address this, it will take me awhile to pour through the books (Frere, Ludvigsen, etc).

faithless

It is certainly more efficient, but not by much. Although the driveshaft may weigh such-and-such amount, its rotational mass is what matters in loss through the drivetrain. Since the mass of the shaft spins relatively close to the center of rotation, it takes very little to move.

Recall those spinning wheels at the science museum, or a ballet dancer?