[wj4]

Hmm interesting, I always thought it was ~20% on dynojet.

[DrDomer]

Originally Posted by wj4

Hmm interesting, I always thought it was ~20% on dynojet.

Ok... I found a AT with dyno of 271HP... a MT with 280 HP... I've seen that people report a 15% drivetrain loss with AT and 13% loss with MT. Then I saw someone else say AT loss was 20-25% and MT 15-20%. Whatever...

So......

AT 271 -----> 339HP with 22% drivetrain loss

MT 280 -----> 342HP with 18% drivetrain loss

So it looks like the STOCK 335i has about 340HP at the crank. Any thoughts?

[sflgator]

Originally Posted by DrDomer

Ok... I found a AT with dyno of 271HP... a MT with 280 HP... I've seen that people report a 15% drivetrain loss with AT and 13% loss with MT. Then I saw someone else say AT loss was 20-25% and MT 15-20%. Whatever...

So......

AT 271 -----> 339HP with 22% drivetrain loss

MT 280 -----> 342HP with 18% drivetrain loss

So it looks like the STOCK 335i has about 340HP at the crank. Any thoughts?

I think that may be a bit high; I'd say that a stock 335i AT is ~ 320-330BHP/340-350 lb.-ft. TQ.

[DrDomer]

Originally Posted by sflgator

I think that may be a bit high; I'd say that a stock 335i AT is ~ 320-330BHP/340-350 lb.-ft. TQ.

Ok... what data do you have to support this statement? I'm trying to base my posts on data from dynos from tests on these forums and estimated drivetrain loss. One camp thinks 15% drivetrain loss another 20%. I posted numbers based on both. I would much rather have actual drivetrain loss. I think the real question is how do you determine the drivetrain loss? Is there a way to know this (not guess... "I think") other than assumptions? Is there a BMW source for this info? People claim the AT is much more efficient than previous ATs. Just curious I guess. I can't really determine why this would impact my daily life.

[sflgator]

Originally Posted by DrDomer

Ok... what data do you have to support this statement? I'm trying to base my posts on data from dynos from tests on these forums and estimated drivetrain loss. One camp thinks 15% drivetrain loss another 20%. I posted numbers based on both. I would much rather have actual drivetrain loss. I think the real question is how do you determine the drivetrain loss? Is there a way to know this (not guess... "I think") other than assumptions? Is there a BMW source for this info? People claim the AT is much more efficient than previous ATs. Just curious I guess. I can't really determine why this would impact my daily life.

Funny, b/c when I asked Shiv about the drivetrain loss on the 335i, he seems to think that it's a definite number loss from the crank to the wheels, not a percentage. Either way, my car dyno'd the following:

Stock dyno: 265 WHP / 286 lbs.-ft. RWTQ
Xede dyno: 322WHP / 378 lb.-ft. RWTQ, + 57WHP / +92 RWTQ

I've only been "using" and/or quoting the 15% AT drivetrain loss b/c that seems to be what the majority of ppl think (and I read somewhere that 15% AT / 13% MT was documented by BMW, although I've never seen this), so I just want to stay consistent. If you do the math with my numbers at 15% loss, the I started out (stock) with 312BHP and 336 lb.-ft. TQ (still much more than BMW's "official" numbers of 300BHP/300 lb.-ft. TQ) and after Xede, I'm at 379BHP and 445 lb.-ft. TQ.

I said it's probably somewhere around 320-330BHP / 340-350TQ b/c I'm just averaging what I got on the dyno (which was a bit lower than some other stock 335i's), what other Xede 335i's got on their dyno's, and what the car mag's got on their dyno's (like AutoMobile Mag's 2 tests on the 335i and Edmunds.com's test on the 335i). Even if it's a little under/over...does it really matter?

[musc]

There is really no way to officially determine the drivetrain loss unless the engine was dyno'd at the crank, then rear wheels. 15-20% is a pretty common range that people assume for drivetrain loss, with automatics incurring more loss than manuals.

Using percentages is pretty crude and inaccurate. Shiv is right on this one. The loss is a definite fixed number of horsepower, not a percentage. This amount of hp loss stays the same unless you change something in the drivetrain (transmission, gears, driveshaft, clutch, converter, etc) For example, if the HP loss for an AT tranmission was 35, with a 335i making 265 at the rear wheels, the loss would figured at approximately 11.7% based on 300hp crank HP. Now if we add the Xede and make 322 hp, the 11.7% drivetrain loss would make 360 crank; however, knowing that the 35 hp loss should remain constant, then the crank HP should be 357. Now this seems like a small difference, but as you can imagine, the more HP you make, the more significant the percentage becomes. If you start off using 15-20%...you are going to see some huge discrepancies.

Regardless, Crank HP only carries significance in marketing... particularly with guys selling these high HP turbo kits. The crank numbers are always inflated since they use a % drivetrain loss, which is incorrect. In the real world, the more significant number is rear wheel hp/tq.

And as far as newer automatics requiring less HP to turn than older ones, this is likely true. Different internals, less friction, etc within the transmission help determine this.

[sflgator]

Originally Posted by catm3

There is really no way to officially determine the drivetrain loss unless the engine was dyno'd at the crank, then rear wheels. 15-20% is a pretty common range that people assume for drivetrain loss, with automatics incurring more loss than manuals.

Using percentages is pretty crude and inaccurate. Shiv is right on this one. The loss is a definite fixed number of horsepower, not a percentage. This amount of hp loss stays the same unless you change something in the drivetrain (transmission, gears, driveshaft, clutch, converter, etc) For example, if the HP loss for an AT tranmission was 35, with a 335i making 265 at the rear wheels, the loss would figured at approximately 11.7% based on 300hp crank HP. Now if we add the Xede and make 322 hp, the 11.7% drivetrain loss would make 360 crank; however, knowing that the 35 hp loss should remain constant, then the crank HP should be 357. Now this seems like a small difference, but as you can imagine, the more HP you make, the more significant the percentage becomes. If you start off using 15-20%...you are going to see some huge discrepancies.

Regardless, Crank HP only carries significance in marketing... particularly with guys selling these high HP turbo kits. The crank numbers are always inflated since they use a % drivetrain loss, which is incorrect. In the real world, the more significant number is rear wheel hp/tq.

And as far as newer automatics requiring less HP to turn than older ones, this is likely true. Different internals, less friction, etc within the transmission help determine this.

Good explanation...makes sense. Thanks.

[DrDomer]

yea... thanks...