I am going to take a wild guess, and say you are wanting to calculate your flywheel hp based on your rwp numbers. Correct? The best way to do this is to have the stock numbers from the dyno used on your car. Compare this to the 340/390 numbers advertised by Chrysler. This gives you your multiplier, and includes the entire drivetrain loss. Using the numbers on GSM.. site, I calculate about a 30% loss. I did this by looking at the advertised gains of the sc and subtracing the gain numbers advertised for rwhp and tq. This gave me a 266rwhp and 290 rwtq. Again, this could very from dyno to dyno though. On my STi, I was only getting 317 rwhp on a mustang dyno, however, a stock STi on that dyno would only get 211 rwhp. I think it is about a 39 % loss on that dyno.
I am also a little confused, as I thought the power numbers advertised on American cars was whp. A friend of mine had told me this, who is really very knowledgeable about such things, in a discussion of the srt-4. That came up due to the fact they are so quick for 230 hp, and the STi has 300, but really very equal in performance. I now think, as I have read in some posts, the hp number is actually a little underrated on the srt-4, and must be fw hp.
Hope this helps a little, as I am not exactly sure what you are asking for.
BTW, these are great cars, my poor wife doesn't even get to drive her car when we go anywhere now. We never fought over who drove the minivan.... ;-)
A 5 or 6 speed car will usually lose about 15% between the flywheel and rear wheels. Automatic cars will lose about 20%. 340hp- 20% will be about 272 at the rear wheels. Take the SRT-8s rated 425hp and your looking at about 340rwhp. Pretty close. Most of them have been dynoing in the 350-360 range stock. Either there is less driveline loss or that motor is underrated.
Steye, your numbers are way off. Usual figures for a RWD car are about %20, FWD maybe %15, AWD, a bucketload Mustang dyno shows less, always, how much less, I"m not sure. As far as the SRT-4, the 230 is indeed supposed to be the crank. But is always shown at the wheels, Heres whats up.
The SRT guys use the worst case conditions, and I mean Death Valley in Aug, heatsoaked, crappy 91 octane gas. So, unless your dynoing under the same handicaps, you'll get a lot more. And show he official rated numbers at the wheel. For the SRT-4 anyway. See, since a turbo motor suffers disproportionately from heat, it also gets a real solid bump from good temps. So, the SRT-4 is real bad choice to showcase the realtionship between crank and wheel.
Now, the SRT-8s have some of the same thing. Not as much, becuase the N/A motors dont lose as much due to heat. Since they dont have the compressor heating up the intake charge, they dont get affected as much. This, I feel, explains why they seem underrated. What SRT sees from these motors at 110 degrees after a few WOT runs is way less than we see at 75 degrees with 170 degree coolant.
Now, do the 5.7s get tested this way? I cant say. But SRT numbers should not be used like regular crank numbers. From what I've been able to find out, my thought is that this drivetrain shows about a %17 loss.
Now, with all this said, why bother? Just say what you got at the wheels. TRying to correct back to crank is like correcting your strip times for altitude or DA. Just report the facts, no corrections.
You are right. My numbers were way off. When I went back to double check, even with the numbers from GS Motorsports, I got a 21% loss. I also double checked the math on my STi loss with the Mustang dyno, and got 30% (at least I was doing a consistant screw up . In short, to convert whp to flywheel, I think you would multiply the wheel hp by something like 1.25 to get there.
The one thing about converting back to flywheel, is it puts different venders on the same playing field when comparing mods.
Thanks for catching my errors, and the srt-4 enlightenment.