318is and 3.91 LSD on the track

Post Wed Apr 01, 2009 2:38 pm

I have a track day coming up with my 318is, it’s pretty much standard apart from an evolve chip and slightly lower suspension. When I’ve previously had it on the track I’ve used the standard open 4.10 diff but I fancy a bit more sideways action this time around. I have a 3.91 lsd I bought recently, but I’m also in different to welding up the open 4.10. In my mind what I choose will be down to how it will accelerate. I’ve seen people on here suggest the 3.91 will be too long for track work on the 318is which has made me think about welding the 4.10. If anyone has any experience with using a 3.91 on an 318is I’d be very keen to know your opinions. Before the track day the car will also be mildly stripped.

Cheers

Post Wed Apr 01, 2009 4:19 pm

Most 318iS owners go for the 3.91 as its the closest to the ideal and rocking horse shit 4.10 LSD.

If it was a 3.64 then I'd say worry about the gearing being too long but I don't think you'll be disapointed with the 3.91. Some one will come along to prove me wrong but thats my two cents

I know nothing about welding difs so I'll be interested on the answer to that, I've yet to make the same decision on my iS

Post Wed Apr 01, 2009 4:25 pm

I'm not afraid of welding diffs (I have one on my E21 though I haven't used it yet), but if the ratio doesn't make much difference I'll stick on the 3.91. Might be better to use the LSD since my not so track experienced friend is going to be driving that day also...

I'm right in thinking that I can use my 318is driveshafts and diff flanges and all I have to do is adjust the prop length slightly?

Thanks

Post Wed Apr 01, 2009 5:10 pm

Was there a standard 318is LSD? If so, what was the ratio?

Post Wed Apr 01, 2009 5:31 pm

4.10 so I'm told

Post Wed Apr 01, 2009 5:39 pm

and they're 'rocking horse shit'....

Bugger...

Ta.

Post Wed Apr 01, 2009 5:46 pm

some people use the 4.27 - which is good for lowering the final drive, again rare as heens teeth !

Post Wed Apr 01, 2009 5:53 pm

juniorGT wrote:some people use the 4.27 - which is good for lowering the final drive, again rare as heens teeth !

Rediculously so, a 4.27LSD would be ideal for my touring if it was staying M42 powered for any great length of time.

Post Wed Apr 01, 2009 8:09 pm

As discussed on another thread (http://www.e30zone.net/modules.php?name ... c&t=128914) you could also alter the gearing by using different diameter wheel/tyre-profile combinations....

Post Thu Apr 02, 2009 11:43 am

Funnily enough I'll be using 14s on the track - but most likely with the standard E30 sized rubber, so it shouldn't really be too much overall diameter change. I think I'll stick on the LSD and see how I get on, unless anyone else has any opinions?

Cheers

Post Thu Apr 02, 2009 12:52 pm

I wouldn't run 65 profile tyres on track! The tyres will flex around a crazy amount!

Post Thu Apr 02, 2009 1:05 pm

Austinspace75 wrote:Was there a standard 318is LSD? If so, what was the ratio?

LSD was on option when the car was new, ratio 4.10.

Post Thu Apr 02, 2009 2:08 pm

Jon_Bmw wrote:I wouldn't run 65 profile tyres on track! The tyres will flex around a crazy amount!

Probably so but the tyres aren't any use on the road so they need to be used up! Plus I haven't got enough cash to buy tyres I'm going to wear out in a day. I'm not sure if they are all 65s actually, and for most part I think I've got a set of 15" BBS with tyres to finish off. It must be said this is an airfield day, rather than an actual racetrack and I'm more concerned with having fun than being quick

Post Thu Apr 02, 2009 2:23 pm

No worries, I am pretty sure 14" bbs standard size is 195 65. I was just concerned, with extreme force, its concievable that it could pull a tyre off the rim I guess. That could be unpleasent. Best to try it out, but I suspect you'll notice a big old difference with the 15's.