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View Full Version : Loss of Power due to AWD drivetrain



nebolic
03-10-2005, 11:04 AM
Okay so I'm just wondering, how much horsepower are we losing through our AWD drivetrain. I'm getting figures anywhere between 15% to 30%. Anyone wanna have a crack at it and see what you can come up with.

Nebo

warpspeed
03-10-2005, 11:38 AM
Usually on a 2-wheel drive car, you lose @20%. On ours I would say between 25-30%.

JanSolo
03-10-2005, 11:42 AM
Usually on a 2-wheel drive car, you lose @20%. On ours I would say between 25-30%.

I thought a 2wd car was about 15%? At least, that's what I was told by the tuner for my old 300zx tank.

nebolic
03-10-2005, 11:56 AM
Hmmm interesting, cause I've been talking to some of my STi buddies (stock) and they dynoed in at around 230WHP to 235WHP which equates to around ~22% loss.

With the Evo's i believe we've seen that they are putting down around (stock) 210WHP to 215WHP which also equates to a 20%-22% loss. I'm just wondering how people are coming up with the 30% loss, that is a huge number.

Nebo

MarkSAE
03-10-2005, 12:58 PM
Usually on a 2-wheel drive car, you lose @20%. On ours I would say between 25-30%.

I thought a 2wd car was about 15%? At least, that's what I was told by the tuner for my old 300zx tank.

A front drive transaxle setup will have less drivetrain loss compared to a front engine/rwd setup. It has a more direct drive w/ less parts to spin.

My guess is a FWD setup would lose roughly 15%, RWD 18%, AWD 23%.

wilson1
03-10-2005, 02:22 PM
FWIW, I spoke with a person from an knowledgeable source, hp loss is a constant hp loss, so it you have a fixed baseline run, and the loss is ,say, 50 hp, then, that's the amount of hp loss regardless of the amount of hp increase. It seems to make sense as if you think about it, if you increase the hp by another 100, does it really takes another 25 hp to turn all the parts if the driveline loss is presumably at 25%, as once the driveline is running, it's does not take more hp to spin or move them. So what does it boils down to, i that there is a constant hp loss for each specific driveline.

hellz Evo
03-10-2005, 03:14 PM
I agree with wilson. If you increase horse power the the loss percentage would decrease. Because it will always take the same amount of power to drive those components.

Buzzard
03-11-2005, 09:17 PM
I recall a post on an english evo site that showed a shop tested this in a Evo6 (I think). They bench dyno'd the engine then tested it in the car on a awd dyno (don't know which type). They found a 23% loss. This is always the number I use. Also, I was told to expect around 18% loss with my RX-7. Of course these numbers are from my failing memory. :lol:

ez76
03-11-2005, 11:55 PM
hmm, could think about it in terms of the increased power you can put down in situations where FWD/RWD would be traction limited :D

TarmacAttack
03-14-2005, 10:18 PM
Wilson is correct about only losing a constant amount of power rather than a percentage. Here's the tricky part, most people will dyno with whatever gear has the closest 1:1 ratio, so let's say it's 4th gear like evo's are. Let's say you get 220whp base, and the motor is rated at 270. 50hp loss though the drive train in 4th gear. Now let's say you dyno in 2nd gear, what do you think your number will be? I'll bet you make more whp in 2nd because you certainly have less hp loss because of the gear ratio. From my expirence the only true way to get a good idea of how much loss you really have through your drive train is to dyno it in all gears and average it out.

ez76
03-14-2005, 10:29 PM
Wilson is correct about only losing a constant amount of power rather than a percentage.

It doesn't seem to be that simple. Check this out:
http://www.eng-tips.com/viewthread.cfm?qid=74391&page=6

Maldo
03-16-2005, 07:38 PM
Wow, I don't know crap!!!

Anyway, when comparing the Evo loss to the STI loss don't forget one fundamental difference... the Evo's motor is transversely mounted (the crank runs from left to right) while the STI's motor is not (the crank runs from front to back). I don't know how it works for sure but wouldn't this mean that the Evo's transmission has one additional turn in order to get power to the center diff?

Jesus, I think I just confused myself!

TarmacAttack
03-17-2005, 01:06 AM
Wilson is correct about only losing a constant amount of power rather than a percentage.

It doesn't seem to be that simple. Check this out:
http://www.eng-tips.com/viewthread.cfm?qid=74391&page=6


Good article, let's get into that. Oil bath accounts for >1% of drivetrain loss. Since you need oil to lube and dissapate heat from gears and bearings. So what it robs in hp, it makes up for it in heat reduction.

CV joints, axle bearings, hubs, account for 2% drivetrain loss on a dyno and on the road I would say about 3-4% depending on how long you've driven for. Remember on a dyno there's less load on these components so you don't build up as much heat. Which brings up another thing about heat, transaxles and dynos. Transaxles won't build up as much heat on a dyno as say driving for an hour because there's almost no load on the drivetrain. So on a dyno you acutally have less powerloss due to the drivetrain.

I'm sure there is a small percentage of drivetrain loss that is variable, but not to the extent where it'll be over 5% of the total loss since there's are variables like heat, lubrication, wheel size, etc. Even if you take out wheels and use a chassis dyno, then you still have cv joints, less load. The only consistant that I know of is gear cuts, gear size, and amount of gears used to transfer energy. That will always be a constant.


Wow, I don't know crap!!!

Anyway, when comparing the Evo loss to the STI loss don't forget one fundamental difference... the Evo's motor is transversely mounted (the crank runs from left to right) while the STI's motor is not (the crank runs from front to back). I don't know how it works for sure but wouldn't this mean that the Evo's transmission has one additional turn in order to get power to the center diff?

Jesus, I think I just confused myself!

As fundamental as having a normal engine config is, you still have 3 differentials that take up just as much power as most awd cars. STi specific, I could see where you would have more efficient power going to the center diff then to the rear wheels and more of a drivetrain loss going to the front wheels because you need to transfer the power transversly, but then again you could make up for that with the correct gear ratio's. The only difference would be that you could make the STI rwd easier, where as it would be a fwd for the Evo.

CollinsT
03-17-2005, 06:42 PM
umm I have always wondered this same thing

Kamikaze
01-04-2007, 10:52 PM
How about the torque that you measured on a dyno? Is the torque also reduced in the drive train?

UCB
01-05-2007, 04:31 PM
holy old thread batman 8)

Yes...since HP simply a function of torque, its the torque thats ultimately being reduced from drivetrain losses

Is say 25% is about correct, but I never understood what all the fuss was about, all that really matters is whats measured on the dyno (and the deltas), as those numbers are what correlate to track times

Who cares if you have 400bhp when you are still getting out run by stock Z06s

MarkSAE
01-05-2007, 04:50 PM
It'd be nice if someone who had both a chassis dyno and engine dyno could do pulls on both and plot out the differences. Let's say do runs on each dyno at 5 different boost levels to get values for 5 different horsepower levels.