I have a 1992 325i sedan (E36). Whenever I open up the throttle, I never feel like I'm getting enough power to the wheels, I can't decide if I want to get a limited slip differential or a performance clutch and lightweight flywheel. The ones I'm looking at are pretty close in price so value isn't really an issue. Which offers the biggest night/day increase in performance? Whichever I go with, I want to install it myself, a friend's uncle knows transmissions and can guide me through the clutch/flywheel, but how difficult is it to swap a differential? Not the whole thing, housing and all, but the diff itself. Anyone know of any online DIY instructions? Thanks, sorry this is so long.
The _easiest_ thing to do would be to get a stock BMW lsd diff for your car (presumably of the same ratio as what you have), and swap it out (which is relatively easily done), and see if you notice a 'diff' (ha-ha). Ebay's always a bit of a gamble, but if you shop carefully, that might be a good source. Roundel classifieds, advertisers, or local junkyards are other options. I think swapping out diff internals is best left to experts. It's not impossible to do or learn, but I think there's an experience-based art to getting a lsd together properly (shims, more shims, & pre-load, OH MY!) Anyway, I think you probably might find a good lsd for $450 (roundabouts) or less, maybe a good bit less. If the car is otherwise stock as is, the stock clutch, if it's functioning as it should, should be adequate to get the engine's power through to the tranny and driveshaft. In other words, if the clutch is good, I don't know if it, or the flywheel, are gonna make much of a difference in terms of what your sensing about getting the power down. That doesn't mean you won't feel a difference - a lighter flywheel should let the engine spool up more quickly. I think stock BMW clutches are typically more than adequate for stock engine hp; if you bump up to 300hp or more, I think that's the range where a performance clutch might start to be important. The E36 Bentley manual might cover diff rebuilding, not sure if it does. Try some googling, Pelican Parts seems to have an extensive tech-tips section online. I think a lsd would be helpful w/ off the line motivation (plus handling, and snowy weather handling). You could stick 5000 hp in there (well, not really feasibly, but.. you know..) and a tin-can lid for a flywheel and clutch, but that won't do you much good if the diff's freewheeling and only one wheel's spinning its tire off. Don't forget performance tires either - if you've got mediocre rubber on there, that won't help much either.
Torque vs RPM If an increase in actual performance is what you are after swapping differentials is the way to go and a much overlooked performance modification especially for BMW's. 3 series BMW's especially respond very well to a differential gearing change, that is a lower final drive, high number. Changing out the differential as a unit is the way to go for this as BMW nor anyone else in this country sells retail differential internals. Just buy the complete unit and swap it out. A DIY project for sure and a good one.
I got lucky, because my 325is is a '92 and it happened to be one of the few that came with an LSD. After driving one without, I have found that the difference coming out of a corner is staggering. I'd say that its one of the most important things you can do for your car, performance-wise.
