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      03-08-2009, 09:33 PM   #1
hl0m4n
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Question Driveloss Question

what is the drive loss % for 355i auto and manual? so we just multiply this # with dyno # and that gives us crank (engine) correct? thanks guys.
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      03-08-2009, 11:42 PM   #2
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Sort of. I've seen a bunch of numbers thrown around, I think you can search for them to see.

The important thing to remember is that drive line losses are not linear. If you are at 18% for the MT, and you add 100 hp, you don't necessarily lose 18% of the added power. However, for the sake of most arguments, and the relatively small changes we are usually looking at (no one is doubling the output on a stock tranny), you can assume they are linear, and your equation above would hold.

I think I remember 18% for the MT?
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      03-08-2009, 11:52 PM   #3
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You sure it's that high? I thought I've seen stock dynos around 270 WHP, which would suggest 10% if 300 HP is true, and slightly over that, if BMW has in fact under-rated their engine and the true crank HP is more like 310 or so.
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      03-08-2009, 11:54 PM   #4
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Not sure at all. I've not been able to dyno mine (xi), so I'm not sure at all.
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      03-09-2009, 12:08 AM   #5
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xi is going to have a higher drive train loss then rwd models.
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      03-09-2009, 12:09 AM   #6
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Pretty sure DT loss is 13%(MT) and 15%(AT).
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      03-09-2009, 12:10 AM   #7
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Quote:
Originally Posted by Rotary Rasp View Post
xi is going to have a higher drive train loss then rwd models.
Yeah I know. Lower power cars can run 15% - 18% on a manual, but I think the BMW may run less.
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      03-09-2009, 12:13 AM   #8
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i would love to know the loss on a 6MT XI ?
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      03-09-2009, 01:06 AM   #9
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whats up dan

ive heard 6MT rwd is around 12% and 6AT is around 15%

I usually multiply dyno numbers x 1.12 to get the approx crank hp

if you have an xi, thats a whole different story
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      03-09-2009, 01:55 AM   #10
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Quote:
Originally Posted by Lotus99 View Post
You sure it's that high? I thought I've seen stock dynos around 270 WHP, which would suggest 10% if 300 HP is true, and slightly over that, if BMW has in fact under-rated their engine and the true crank HP is more like 310 or so.
Well, I dynoed my 335i MT on a dyno, which shows crank hp. It was 319hp. Another two 335i's MT - 315hp and 340hp (something's "wrong" with the car as he killed me by 4-5 car lengths 30-130mph).

I'd say it's 15-18%.

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      03-09-2009, 02:58 AM   #11
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No. 12% MT and 15% AT is right
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      03-09-2009, 03:20 AM   #12
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Quote:
Originally Posted by munters View Post
No. 12% MT and 15% AT is right
In such case my stock 335i puts down 281whp, and acquaintances' of mine - 277 and 299 whp accordingly.
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      03-09-2009, 05:48 AM   #13
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Yep that sounds about right.
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      03-09-2009, 08:14 AM   #14
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Quote:
Originally Posted by munters View Post
No. 12% MT and 15% AT is right
+1

12% MT and 15% AT for the 335i
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      03-09-2009, 11:05 AM   #15
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what about MT & AWD ?????
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      03-09-2009, 11:25 AM   #16
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If you see JPsimon and his numbers, he has about 10 hp less then another with the same mods and 2-WD. It's amazing... Not a big different.
But we don't know jet.
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      03-09-2009, 11:34 AM   #17
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Quote:
Originally Posted by sd390r View Post
whats up dan

ive heard 6MT rwd is around 12% and 6AT is around 15%

I usually multiply dyno numbers x 1.12 to get the approx crank hp

if you have an xi, thats a whole different story
The correct calculation should be your dyno number divided by 0.88 to find crank hp.
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      03-09-2009, 11:46 AM   #18
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MT = 16%
AT = 18%

415 HP M3s dyno around 350rwhp. Which would indicate 16% drivetrain loss for the M3. And their is no reason to believe a 335s drivetrain is more efficiant than an M3s
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      03-09-2009, 12:36 PM   #19
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Quote:
Originally Posted by hl0m4n View Post
what is the drive loss % for 355i auto and manual? so we just multiply this # with dyno # and that gives us crank (engine) correct? thanks guys.
Be very careful in trying to account for drivetrain loss. As others have stated, it is not linear and there are a ton of variables from tire pressure to trans oil temps etc that will throw it off a lot. Rumors of AWD having a significantly higher drivetrain loss vs RWD are typically exaggerated IMO.
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      03-09-2009, 12:43 PM   #20
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This is the best data i have seen on drivetrain loss: http://www.dinancars.com/assets/File...A%20EDITED.pdf

See the end of the sheet where loss is given per RPM and more or less linear between 8,5% (2500 RPM) to 13,5% (7000 RPM) I don't know if this is a manual or auto.
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