M-3 BMW differential

[ront49]

I have a BMW M-3 independent suspension rear end in my Backdraft. Engine is a 418 stroker pushing approximately 500hp. No, I haven't had it on a dyno yet. My question is, how much hp will the M-3 handle? Since I've not had it dynoed, I don't really have an accurate figure on the hp or torque. Kind of thinking I'd like to take the BDR to the drag strip but don't want to tear up the rear end.

[spdbrake]

This thread may help

Differential Strength

[BDR_Boy]

Perhaps also worth considering…

https://store.activeautowerke.com/pr...racket-dsb-e36

Haven’t bought or installed one myself… so no firsthand experience with it.

[1985 CCX]

Guess my M is ok then as its only 342hp

[Cashburn]

Depends which diff you actually have... but they've held up fine to 500hp in nearly 2,000 cars now.

The halfshafts would be the question mark. Would depend on when your car was produced to determine which generation/design you have.

[66AC]

What was the largest HP engine that BMW married with the M3 Differential?

[ront49]

Originally Posted by Cashburn

Depends which diff you actually have... but they've held up fine to 500hp in nearly 2,000 cars now.

The halfshafts would be the question mark. Would depend on when your car was produced to determine which generation/design you have.

My BDR is build #151, mfg. 2004

[Shizznizz]

Easy check: If your diff flanges got 6 bolts, its a 188mm diff, if 8 bolts its the upgraded 210mm diff.
188mm diff on BMW race/drift cars were fine up to about 400hp, the 210mm are considered bullet proof regardless of the hp.. traction would be your limit, and even destructive drifting driving is not able to wreck them. They have stronger ring gears, stronger output shafts etc.
I've got a 210mm on my Backdraft, but its actually very rare and built on request. Their BMW subframe is only compatible with 188mm diffs as far as I know.

[spookypt]

188 are fine but like anything the more stress u put them under the more likely they go bang. I’ve lunched a heap of 188s in my BD but under super harsh racing conditions.
So to answer a few things as per above. I run a 210 now and it’s good. It has 6 bolt 1/2 shaft flanges cause I built it that way. The 210 with a few mods fits nicely into the 188 cradle. I have 571 Rear wheel hp and slicks so it’s under some loads.

One of the big factors is ratio. You need meat around the pinion gear. Short ratios are weaker like 3.91, 4.27 etc. 3.91 is the beginning of seeing issues. I also run diff pump and cooler and change oil a lot to maintain longest life.

Imo the 188s are fine but once you start getting serious with HP and racing bigger is better.

[hauss]

I have had my passenger side shear the bolts on the passenger side I have a 600 hp 427 stroker motor . my fix was re tap threads on flange diff side install 1/8th longer bolts and red locktite. haven"t had any more issues . I check the back of the flange to make sure the bolts are staying tight. hope this helps.

[ront49]

I'm not looking to drag and push my BDR to the limits however, I'd hate to strip the ass end out of it just in case I was forced to let someone know what they were dealing with. Not that "I" would ever consider exceeding the legal posted speed limit ... no, not me!