RWHP Conversion to Flywheel HP?

[Jason Heffner]

The correct way to correct for driveline loss is to divide your rwhp by .85. This will factor in a 15% loss which is roughly what you lose on a Viper.

 

[Venom Lover]

Though if you look at the FAQ , the conversion factor appears to be 13%, in which case you would use fwhp = rwhp / 0.87.

 

[ACR Joe]

Hard to believe that the delta could actually be 13% to 15%. That's quite a bit to lose in the driveline. Does anyone have hard data to substantiate this correlation?

 

[ACR Joe]

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by JMcGuire:
I've read that a lot of the more typical sports cars are even worse. If I recall correctly, '00 Mustang GTs are something insane like 25%.

<HR></BLOCKQUOTE>

OK, consider this. An engine makes 500 bhp and 450 rwhp so the driveline loss is ~10%. That same engine is then modified to produce say 750 bhp; will the driveline loss still be 10%? No, it will be ~6.5% and that's my point. Assigning a fixed % value to driveline loss is inherently flawed. Driveline losses should be expressed in absolute rather than relative terms. Any digit-heads out there care to comment?

 

[Bill/APEX Motorsports]

We dyno a LOT of cars here, and we typically see right around a 15% driveline loss on stock cars w/ manual transmissions, assuming they're actually making the flywheel hp that the manufacturers claim.
While it's impossible to say "This car makes XXXhp at the rear wheels, so it definitively makes YYYhp at the flywheel," 15% is the best and most accurate number we have to use. We're basically going off of an assumption, and there's nothing wrong with that, as long as everyone's on the same page.
Dynos are fairly accurate, but the numbers they produce should be used as a baseline for future modifications.
By the way, Mustangs are usually right in the same 15% ballpark...

 

[JonB]

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by ACR Joe:
... Assigning a fixed % value to driveline loss is inherently flawed. Driveline losses should be expressed in absolute rather than relative terms. Any digit-heads out there care to comment? <HR></BLOCKQUOTE>

Joe.....did you say the conclusion bass-ackwards? I agree with your premise, but not your conclusion ! [Logician Mr. Spock would be pi$$ed.] Driveline loss SHOULD be relative, right?

But I also agree w/ Apex-Bill...... RELATIVE to 450-550HP Viper, 14-15% is about right. I have also had this debate w/ the dyno-bustin' gearheads at UniTrax......and the "relative variable" is quite low, but still real.

2% of 1200HP matters. 2% of 450?

 

[KenH]

I think some of the high driveline loss numbers you see on cars like Mustangs is due to the fact that the car mags just assume that the difference between the Mfr. listed flywheel HP and RWHP they measure is all due to driveline loss. The fact that some cars just underperform compare to their published spec, like the recent infamous Cobra debacle, is completely glossed over. I wish the mags would either pull the engines for the test to compare against published spec, or the manufacturers should start using RWHP as the standard.

--- Ken
'01 GTS