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E90/E91/E92/E93 (2006 - 2013)
The E9X is the 4th evolution of the BMW 3 series including a highly tuned twin turbo 335i variant pushing out 300hp and 300 ft. lbs. of torque. BMW continues to show that it sets the bar for true driving performance! -- View the E9X Wiki

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Old 02-16-2014, 11:02 AM
Duncmasterfunc Duncmasterfunc is offline
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Location: New Hampshire
 
Join Date: Jul 2013
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Mein Auto: 2009 BMW 335d
Question regarding max torque on 335d transmission

So I've got a 2009 335d and all I can say is that I'm head-over-heels in love with this machine. So much torque, so much comfort, and and remarkable fuel economy (particularly on the highway).

I've been reading up on doing a DPF delete on it (already out of warranty) as a quick and cheap way to eek out some more torque. Browsing stuff online I've found people who can get over 500 ft-lbs (up from the stock ~425) with just a DPF delete and a retune. Sounds too good to be true.

My Google-Fu has revealed that the ZF 6HP26 transmission in the car is rated for 443 ft-lbs. I know that manufacturers typically build in some tolerance to their systems, so the transmission might be able to take a little more than the specified max, but I feel like if I were to go over 500 ft-lbs I'd just end up shearing the teeth off of my gears. Common sense seems to dictate that this would be a bad idea.

So I guess my question boils down to this:
How much tolerance is typically built into these transmissions? Would putting 500 ft-lbs of torque onto a transmission system that is rated for 443 ft-lbs be too risky?
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Old 02-16-2014, 12:56 PM
anE934fun anE934fun is offline
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Location: S.F. Bay Area
 
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Mein Auto: 2010 335d
Typically failures occur in the torque converter and gear shafts when too much lb-ft are applied. If you are planning on drag racing, then 500+ lb-ft will probably result in failure of a stock 6HP26 fairly quickly, absent internal mods to handle the extra lb-ft. The car has been engineered for a specific performance envelope. Expect things to fail the more you try to push the envelope. First the transmission will go. If you beef up the transmission, the next thing that will fail will be the differential. And, and, and.
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Old 02-16-2014, 05:22 PM
jburke4689 jburke4689 is offline
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Location: Ellicott City, MD
 
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Mein Auto: 2007 335i
It is a mistake to think that manufacturers build tolerance beyond spec into transmissions or engines. That may have been true in the past but it generally isn't today. Today they are more likely to assume a transmission tan take more torque than it actually can and deal with the few failures that occur when a driver maxxes them out.
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Last edited by jburke4689; 02-16-2014 at 05:23 PM.
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