As title states... Has anyone run a 3.91 LSD in their track car? I have found during the last 4 events I have done that my car is needing a higher gear. Currently I have a 3.15 LSD in my car and it has been a very good upgrade, but it seems I am still out of the powerband of my motor during 3rd gear corners, especially at TMP. I found the same thing at shannonville but it was not quite as bad. My only concern is running out of gear on the TMP/Shannonville straights which are 4th gear. Mosport is of no concern as 5th gets me to 215KPH and with my lightly modified motor, I won't be seeing those numbers anyways. So far, I have done mid 1:23's at TMP and I am looking to take the GT2 track record during this weekends OTA event but to do so, I need a little more. In preparation for this weekends event, I have so far removed the complete A/C system, AUX fan, fan clutch and installed a SPAL electric fan kit. Along with all of that, I will be finally installing my M50 manifold w/tune!
Btw, I am only looking for first hand experience as I have already done my research and know what numbers(speed wise) to expect! This is a track only car.
I love it - I basically always run 3-4-5, and never have to drop to 2. With my motor (built M52 - 232WHP), I don't run out of gear at Calabogie, Shannonville, and just BARELY at Mosport on a good run, but nothing serious .... watch some of my vids and you'll see my shift points.
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Shawn
1992 3.0L M52 325i (ex-daily driver - current RACECAR)
2002 330Ci (ex-daily driver - sold!) Check out my e36 track car build
Thanks for the response! I wasn't worried about topping out in fifth, just 4th gear. Having to shift to 5th before turn one at TMP or after the back straight at SMP would not be good but judging by what your saying, I should still be ok.
Btw, what time have you done at SMP Long? I just did a time attack event a couple weeks back and managed a 2:03.8.
I've only ever been to shannonville twice, and it's never been a timed event. On that vid I think my best is a 2:02-2:03, just judging by the clock at the bottom lol... i didn't have many (if any) clean laps - always stuck in traffic, a couple drifts...
Last year I was sitting at around 2500lbs (plus me and the passenger), on 255/40R17 starspecs
If you watch my SMP video starting at 7:45, you'll see that I lied lol. I take that tight corner in 2nd, then do 2-3-4-5 on the back straight - you'll see there's lots of room to keep accelerating before the downshift back to 4th for the right-hander.
Again, not "declaring the law" for how to drive that track, as I don't have much experience on it.
__________________
Shawn
1992 3.0L M52 325i (ex-daily driver - current RACECAR)
2002 330Ci (ex-daily driver - sold!) Check out my e36 track car build
I love it - I basically always run 3-4-5, and never have to drop to 2. With my motor (built M52 - 232WHP), I don't run out of gear at Calabogie, Shannonville, and just BARELY at Mosport on a good run, but nothing serious .... watch some of my vids and you'll see my shift points.
Is that a large case, or medium case your running?
If its the med case, have you had any issues with boiling the fluid or durability?
No I've never had any issues, and I don't even run a finned cover. I had Royal Purple 75W140 in it for the past 2 years (before that was OEM fluid). Last year the input seal started leaking and I changed the fluid this year to Redline 75w90.
When I bought the car in 2005, the diff was already in, and it's now on it's 4th season of autocross/track and still holding strong!
__________________
Shawn
1992 3.0L M52 325i (ex-daily driver - current RACECAR)
2002 330Ci (ex-daily driver - sold!) Check out my e36 track car build
Yes, we never got the large case in the E36 over here. But both the 7 series and M5 came with large case diff in North America, and many people swap it over. There are a few ways to do it.
Either way good to hear the Med case is holding up. That will prolly be the route I end up going anyway.
^I thought you were in the 210-215 range from where I was sitting.
I guess I need to pay more attention lol.
According to diffsonline, I should top out around 215. So maybe I'm wrong. Either way, I don't like having the motor at 7000rpm for the amount of time it sits there.
Same as doogee. I ran the 3.91 lsd. Great on the shorter tracks, but at Mosport, I was running the car hot and topped out on the back straight. The my oil temps were also a lot higher, as I ran it near the top range all the time. I pulled it and I'm now running a 3.23. I believe the 3.46 is the sweet ratio for this car.
I wasn't worried about topping out in fifth, just 4th gear. Having to shift to 5th before turn one at TMP or after the back straight at SMP would not be good but judging by what your saying, I should still be ok. 
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