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Thread: AWD WHP vs 2WD WHP??????

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2009-11-19 03:59:13
AWD WHP vs 2WD WHP??????
scenario: my boy recently upgraded in his WRX from stock to 720cc, 18g, larger TMIC, Walbro, and external wastgate. he hit the dyno for a tune and was there roughly 7 hours. the guy tuning is amazing!!!!! there is still work to be done, but he peaked 260 @ 18psi, and 303 AWHP @ 20psi. what does that equate to in a FWD or better, a 2WD drive? or should the question maybe be: whats the HP at the flywheel? he took me for a hammer and i wasnt impressed at all!!! he was talking like this thing was going to haul ass!!! my little buggy feels stronger! dont get me wrong, it boogies, but im just not impressed with the expectations he built me up to have. he said the dyno was something ive never heard of too....they take the wheels off and install some kind of packs? hes stoked, im happy for him. i just hate to burst his bubble come spring when i still spank him at the track in my "sentra." i ran a flat second faster pig rich and no tune while he was still stock... not to mention my crappy 2.3 60ft. i now have a mild street tune. shes still rich, but certainly stronger and good for 12's all day!!! he will be sad!
2009-11-19 04:01:38
I like to add 3% to the AWHP figure to get RWHP figures.
I like to add 4% to the AWDHP figure to get FWHP figures.
I like to add 19% to the AWHP figure to get flywheel figures.

If you're using dyno packs where the wheels are removed that gives a slight advantage that I like to correct for with another 3% per axle. So really you want to do this:

AWD hub HP to RWHP subtract 3%
AWD hub HP to FWHP subtract 2%
AWD hub HP to flywheel HP add 13%


I wouldn't take that to the bank though.
See top of this thread: http://www.sr20-forum.com/tuning/10391-most-powerful-engines-thread-dyno-thread-powerful-cars-tuners.html
2009-11-19 04:12:41
Honestly my buddy had a 35r kit on his STi. The car made 430whp on not sure what boost level. Definately had more in it but it was a conservative street tune. I won't get into details but lets just say a T25 sentra on high boost was hurtings feelings. Something about those subarus I don't get. I have yet to see one that is holy **** fast. Evos on the other hand, I have seen a **** load of scary fast evo's. I'll report back when I take a ride in my other friends 35r wrx that just made 511whp.
2009-11-19 04:21:09
BEN: im confused! lol
nismo: i agree. ive never been impressed in his car!

at 303 AWD, im assuming hes pushing more at the FLY than my b13. but even with more WHP than me, im still not convinced by SOP HP. not one bit! im assuming hes more than me. by how much, i dont know. i have yet to dyno. id guess from my research here on the forum, im around 275 WHP. regardless, im not even closely convinced by my butt dyno on him being faster!!!
2009-11-19 04:30:57
I've always heard that the power loss through the drivetrain goes like this:
FWD = ~18% loss
RWD = ~21% loss
AWD = ~25-28% loss

these numbers are loss compared to flywheel HP. There are different factors that can alter those numbers, but that's the rough base to go by.
2009-11-19 04:35:38
Actually from what I've seen it's more like this:

FWD = 13-15% (I usually just assume 15%)
RWD = 20%
AWD = 25%

For auto it's more, FWD is like 18-20%
2009-11-19 04:54:36
Yah mine all assumes manual transmissions.

Luka your numbers are way high I feel. But I can't argue with you about them. The best I can do is let you know my theory: e30tech.com Forums

Edit: Reproduced here because membership is needed. To bad you can't read the rest of the thread.

Originally Posted by NoScoE30
Do you agree that a person quoting a crank number when they dont have one (done with a % loss) is foolish?
Yes. If I wasn't clear enough on that point, I apologize.

Originally Posted by NoScoE30
Besides, my engine HP vs wheel horsepower is not even going to be accurate for anybody. (for a fixed % loss)
I'm not sure what you're trying to get at here but I could certainly use the data.

Drivetrain loss is not a constant as I once thought (a given drivetrain will dissipate x horsepower no matter what engine you hook up to it where x is a constant number). Here's an example that I'm familiar with. Nissan quotes N/A SE-R engine at 140 HP to the crank, and everyone gets 120 horsepower to the wheels (give or take). In the "constant" theory, it says 20 horsepower is lost, and even if you raise output of the engine to 300 horsepower to the crank, it will still only lose 20 horsepower to the drivetrain so you end up with 280 WHP. That means people getting 280 WHP on a chassis dyno trying to calculate their flywheel power using the traditional 15% loss formula will result in 322 theorhetical (and completely wrong) flywheel horsepower. This theory is not held by many, and is likely incorrect. The reason given is that frictional losses due to normal forces and fluid sheering actually raises with power. This gives rise to the traditional percentage loss theory.

Perecentage loss theory, since drivetrain losses increase the more power you add, a constant model isn't good enough, and a percentage model makes more sense. I'm not going to explain this one as everyone is familiar with it.

I'm pretty sure most people in the know realize the percentage loss theory is just a decent approximation, and not really accurate. I'm predicting there is a constant loss in every drivetrain due to rotational mass, and then there is a linear or possibly polynomial proportional gain due to fluid friction inside the transmission, transfer case, and differential where applicable.

I'm thinking that some 25 HP is wasted on rotational mass in a typical e30 chassis, and that's not going to change with engine power. If you had stock power in an M20, maybe another 10 HP would be wasted on the fluid friction loss. That 10 HP is 5.72% of the flywheel output. Raise the flywheel output of the M20 to 530 flywheel horsepower (as an example) and I predict you lose the same 25 HP due to rotational mass and the same 5.72% power for frictional losses leaving the engine with a predicted output to the wheels of 530 - 25 - 30.3 = 474.7 WHP.

That's my guess anyway, and I'd love to see your numbers so I can test my theory.

On a side note, someone with 475 WHP applying the 16% RWD formula gets 551 estimated flywheel horsepower. Using my formula they get 527 estimated flywheel horsepower.
2009-11-19 05:36:18
My buddy puts 300whp in his Galany VR4 and when I was putting down 235whp I would pass him up nasty style. I know my car is lighter but I would take him out like noithing.

I feel you need atlease 350-400 hp to feel quick in an awd car lie our cars feel. Thats why i never got into the awd scene. More wheel to turn, more power is needed. But having awd is nice for the launch.
2009-11-19 06:07:35
as i understood it, it was 17% on FWD...but still, my question stands: if hes making 303 AWHP, whats that equate to fly? i think im missing a number to finish the equation. i figured this based upon a 17% loss in a FWD sr20DE; 140 x .17 = 23.8 - 140 = 116.2 sooo, find H for H x .h = ? - H = 303
2009-11-19 06:10:05
It's simple....

303 x 1.17 = 354.51 BHP
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