CWP LSD Question

Fri Apr 17, 2015 7:52 pm

Evening All!

building my E30 into a road rally car.

Im looking to build a LSD unit with a CWP as close to 4.7:1 ratio

What cars should I be looking for for the ratio I need also medium or small case option

Thanks in advance

Fri Apr 17, 2015 8:29 pm

There is a german selling new CW/Pinions on ebay

Sat Apr 18, 2015 12:10 am

Consider using a direct top gear gearbox from an E34/36 etc, if it doesn't fall foul of regulations.
That will make the usual 3.76 - 3.91 medium case diff. ratios the equivalent of 4.64 and 4.83 respectively. (Multiply the ratio by 1.24)

Mon Apr 27, 2015 9:07 pm

Brianmoooore wrote:Consider using a direct top gear gearbox from an E34/36 etc, if it doesn't fall foul of regulations.
That will make the usual 3.76 - 3.91 medium case diff. ratios the equivalent of 4.64 and 4.83 respectively. (Multiply the ratio by 1.24)

I got a 325 Diff with LSD that was recently refurbished for rallying I was told it has a ratio of 3.63.

I'm planning on using an M44 engine so would the standard M44 e36 5 speed gearbox give me the theoretical ratio of 4.50 (3.63 x 1.24)?

What is meant by direct top, is it the gearl lever fits directly into the top of the gearbox rather than on a remote linkage like on my original 316?

Thanks for all the help!

Tue Apr 28, 2015 12:28 am

"Direct top" refers to the input shaft of the gearbox being locked directly to the output shaft in top (fifth) gear. Nothing to do with where the gear lever fits! In this condition the gearbox is effectively just an extension of the prop. shaft, with the gears themselves doing nothing other than spinning needlessly.
A five speed E30 gearbox has a direct fourth gear, since it was developed from an earlier four speed box. The fifth gear is an overdrive gear, where the output shaft turns faster (x 1.24) than the input gear.
AFAIK, the E36 box will have a direct top, although I don't get involved with four cylinder stuff newer than E30s.
Easily checked by putting the box in top gear, turning the input shaft (or the engine crank pulley, if the engine is still attached to the box) and seeing if the output flange turns at the same speed.