Jump to content

BMW E30 diff ratios?


jlucas
 Share

Recommended Posts

There are plenty of people with that data.  There are also cars that swap between the 2 ratios.

 

A motive force versus speed chart will indicate your speed in the different gears of the trans.  It uses final gear ratio to help you determine which rear end will be better at which track based on obvious shift points.

 

In general, fast track, 3.73.  Slower track, 4.10.

Edited by wvumtnbkr
  • Like 1
Link to comment
Share on other sites

That's gonna dep3nd on tire size, how much corner speed you carry, how much horsepower you have etc.

 

If you go through the corner faster, you can carry more gear and go faster down the straight!

 

Do you have any particulars you want to share and a specific track you are looking at?

Link to comment
Share on other sites

I don't have the info you seek. Someone more detailed or fighting for the last 1% of speed can come and chime in...

 

I've run both on a non-aero m20 e30; here are my comments based on running at NCM / Watkins / Pitt / Nelson / Summit Point (Main/Shenandoah): 

 

373:

low shifs/lap, some tracks I never dip into 5th. Unless you have upped the RPM peak, the 3-4 shift puts you outside the power band briefly and puts you in a low torque point. the benefit really is less distraction during a race and better focus on steering / braking. With 245/40/15, rev cut @ 6250 , the peak speed math is 138mph. We've never gone > 120 at the above tracks.

 

410: 

busy AF at some tracks due to really short gearing, but pulls like a freight train coming out of turn6 @ Pitt. The short gearing sometimes puts you in awkward positions like "do I bounce off the limiter in 3rd for 5sec or shift to 4th only to quickly shift back to 3rd for the corner?" I will just short shift early to 4th for longevity. Peak vehicle speed math is 126mph

 

General Comments: 410 busy. 373 chill. I really want to run the car at VIR_Full with the 410 to see what it's like, but I have a feeling I'd be closing in on 127 (non-aero car).

Edited by MichaelPal
  • Like 1
Link to comment
Share on other sites

Based on my theorying it comes down to a track by track analysis. Look at the corner exit speeds and see which diff puts you in the meat of the powerband more often. Also pay attention to points where you need to shift and then downshift very soon after... all else being equal, you want to minimize shifting.

Without actual hard data, 3.73 appears to be best at Road America. Even though our fastest laps have come with the 4.10, it’s a very very small difference and the car / drivers were better at that race for reasons unrelated to diff.
I liked the shift points for the 4.10 at Indy but have no 3.73 comparison.
I loved the 3.73 shift points at NCM full.

 

Obviously this depends on your redline.. some e30 teams will spin to 6700 and some stick to 6300ish, and this difference is big enough that each team may prefer a different diff at the same track. 

Edited by enginerd
  • Like 1
Link to comment
Share on other sites

59 minutes ago, jlucas said:

Thanks guys, our car is also a non aero, 245 tire car, currently with 373 but a buddy had a 410 up for sale so trying to decide if it's worth picking up.  

Buy it.  Try it.  If you don't notice an improvement, sell it for what you have in it.  As I understand,  they aren't losing value.

  • Like 2
Link to comment
Share on other sites

if anyone is desperately wanting a 4.10 lsd, and is coming to HH in march lemme know. since we've juiced up the motor we wont be using the 4.10 going forward and would be willing to let it go at current market rates.

 

or ideally, if you happen to have a 3.64 LSD, would be willing to trade.

Link to comment
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

 Share

×
×
  • Create New...