M50/52 TI Swap

[E36LUVA]

Yeah the only problem with that conversion besides the cost is the 3.15 diff ratio. I want something close to the 3.45 without having to have one put together from diffsonline.com. At roughley $1500.00 its a bit steep right now. The closest used M3 diff I could find to that ratio is from a 96-99 automatic with 3.38 ratio.

[J!m]

I think you will find the 3.45:1 undriveable. The gear is too tall, and the tires spin in all gears.

It sounds cool (and having the nose of the car rise up at stoplights is fun for a few minutes); however it is not fun to drive further than 1/4 mile at a time. Trust me on this.

The 3.23:1 (M Roadster) diff I have now is pretty good, but I would like something a bit taller (3.25/3.35 range), and an overdrive six speed. This would be the ultimate set up, as first is just a bit tall with the 3.23:1 gears, and totally useless with the 3.45:1 gears.

I drive my car close to 400 miles a week (sometimes more) and speak from experience...

[E36LUVA]

I guess there is no way around it huh. I just figured since the M50B25 lacks torque anyway the driveline would survive under normal spirited driving until I could afford something more potent. Thanks for all your input J!m........

[J!m]

It lacks torque is stock trim (but it is still higher than a stock 1.9l) and you are adding a few bits aparently: M3 cams, chip, intake, headers and exhaust, acording to your earlier post...

With all that, you are going to be close to a stock 3.2l motor, which has no trouble breaking the stock ti diff.

[E36LUVA]

The TI diff is basically an E30 diff right. The E36 diff is different than the TI diff. I totally understand everthing you've said but do you know which diff is stronger. I'm pulling at straws here.

[J!m]

The E30 suspension is interchangeable with the ti; however I do not know the specific differences between them. (this is why it is difficult to find M roadster sub-frames: the E30 guys figured out they fit right in, and get 5-lug wheels, heavy trailing arms, brakes and a heavy-duty diff assmebly for their E30 race cars...)

I think its safe to assume that an E30 6-cylinder diff would be safe with the engine you are proposing. But, to answer the question, I do not know if it would be a simple swap with just bolts, or if there has to be some more involved engineering of the assembly to make it work correctly in the ti.

L84THSKY is a good person to ask about the diff, as he just put one together for his car (from an early 5-series if I'm not mistaken), and he had to use E30 parts as well as the 5-series diff and some original ti parts.

I went for the 'easy' route, and installed a complete M roadster sub-frame assembly.

[scabzzzz]

Ive got a rear subframe from a 97 m3. Feels a lot better. And an lsd from an e30 m3. Short gearing. Little hit RPM on the interstate but not too bad. Tops out at like 125ish depending. One important factor to stress is the brakes. Its really forgotten i think when all you wanna do is go fast.

[JedzE36/5]

almost a year later and my stock getrag tranny has held up. that includes my M52, M50 manifold and head, S52 cams and software, Euro MAF, M3 LTW Flywheel and clutch. i am still running the stock 3.45 open diff but that will be gone soon. the stock 3.45 is too tall for me and acceleration is not what i want it to be. i will be coverting it to a 3.73 from an e30. but yea all the swapped tis here use the stock tranny. none have ever broken, including one with a modded S52 that is tracked to hell every year.

the question is, what drive shaft to use when switching the getrag for a 6 cylinder tranny?

[J!m]

I think the standard six cylinder drive shaft will fit.

the M3 drive shaft is the correct length, but most have the six-bolt mounting whereas the ti and other non-M cars (as well as the M roadster/coupe) use four-bolt flanges.

[andy]

Originally Posted by JedzE36/5

almost a year later and my stock getrag tranny has held up. that includes my M52, M50 manifold and head, S52 cams and software, Euro MAF, M3 LTW Flywheel and clutch. i am still running the stock 3.45 open diff but that will be gone soon. the stock 3.45 is too tall for me and acceleration is not what i want it to be. i will be coverting it to a 3.73 from an e30. but yea all the swapped tis here use the stock tranny. none have ever broken, including one with a modded S52 that is tracked to hell every year.

the question is, what drive shaft to use when switching the getrag for a 6 cylinder tranny?

Sounds like I have nearly the same setup. I intially had some problems because it seems like most people use the ZF transmission from the M3/328 while I kept the stock Getrag tranny which is also used by the 325. We found we had to shorten the driveshaft slightly to get it to fit, but it's a lot easier than adding on.

The 3.73 is cheap and easy to find, but I'd be sure to run relatively tall tires, as it's pretty short for the highway. Great on the track, though.