Should I change Diffs?

[winstontj]

I have a 40% 4.10LSD now. When I redo the motor will I want something a little lower geared? It'll be some reasonably powered 2.7-2.8L variant eta cranked M20. I have the ability to use a 3.64LSD with a CR gearbox but somehow I think that would get me right back to where I am.

What do you guys suggest to run for a rear end combo with a more powerful motor and a 5-speed OD box??

Thanks!

[drifty340i]

dont do a 4.1 with a 2.7swap mate, go for a 3.64 or 3.73 and use the tq

[PiercedE30]

How much you want for the 4.10??????????????????

[winstontj]

its a 40% LSD rebuilt in 2001 so i probably will not sell it. It cost the PPO about $1,200 to get all the work done on it and I can't sell it for more than a few hundo so I'll let it collect dust till I get a track car in a few years.

If I were to run a cr gearbox would the 3.25lsd be the best choice or should I look foe something taller? Is there a 3.10 or close?

[FredK]

I think 3.25 will be fine if you have a 1:1 5th.

I'd get a 3.46 if you want slightly more mechanical advantage. I have one and it's not that annoying at highway speeds.

There is a 3.15 from a Z3 2.8; IIRC it is Torsen and not the traditional disc clutch type.

[winstontj]

FredK are you running a 3.46 with a OD or CR gearbox? I'm not 100% sure if I want to run the CR box. The way I see it the only real reason there is to really run a CR box is mostly for bragging rights... which I may be after here.

I'll look at a 3.46 or a 3.64 or if I do the CR maybe the 3.25. Do you think I could use the 3.46 for both? Would that be the most similar to the OD with a 4.10 or is there not really any interchangability between gearboxes with the same rear end #???

[PiercedE30]

I have a 3.46 LSD sitting next to my toolbox at work. I've got it pulled apart at the moment to R&R it and polish the gears.