Looking for a 4:10 LSD

#1

We are currently running a 3:73 LDS and need the lower gearing of a 4:10 LSD. I am open to an outright purchase or a trade if interested.
I live in Leesburg, VA.
Best,
-Russell

#2

I hope this is not for a Spec E30 race car. :huh:

#3

ChumpCar with an slushbox running a stock M20.

We need the 4.10 for additional oomph out of the corners to keep up with the sticks. Additionally, IMO, the 4:10 should give us additional top end. Here is my rational. Our current setup hits the rev limiter in 3rd at 122 mph (indicated) or 116 mph using the gear calculators (details below). Changing to a 4.10, the shift to 4th would be at 106 mph (calculated) with the rpm in the sweet spot (~4475 rpm) and pull strong beyond 116. Note that 3rd in the auto is the same gearing as 4th in the 5-speed. However, the gearing for 4th the auto is a 0.73 vs. 0.81 for the sticks so that would be like you guys shifting into a theoretical overdrive 6th. Needless, with the 3.73, our 4th gear is useless hence why we need the 4:10.

Feedback is welcomed.

Assumptions
Tire Diameter for a 205/60R14: 23.68”
Redline: 6150 rpm

Gearing for the autos (ZF 3hp 22h or the ZF 4hp 22h)
1st 2.48
2nd 1.48
3rd 1.00
4th 0.73

Calculated max speed in gears with auto using the 3.73 diff at redline:
1st 46.8 mph
2nd 78.5 mph
3rd 116.1 mph
4th 159.1 mph

Calculated max speed in gears with auto using the 4.10 diff at redline:
1st 42.6 mph
2nd 71.4 mph
3rd 105.7 mph
4th 144.8 mph

For comparisons to the 5-speed

Gearing for the 5-spds (Getrag 260)
1st 3.83
2nd 2.20
3rd 1.40
4th 1.00
5th 0.81

Calculated max speed in gears with 5-sp using the 3.73 diff at redline:
1st 30.3 mph
2nd 52.8 mph
3rd 83.0 mph
4th 116.1 mph
5th 143.4 mph

Calculated max speed in gears with the 5-sp using 4.10 diff at redline:
1st 27.6 mph
2nd 48.0 mph
3rd 75.5 mph
4th 105.7 mph
5th 130.5 mph

#4

6150? I haven’t owned an auto but I’m pretty sure it should still be 6450. Make sure you don’t have a 525 ECU. My 87 IS would hit a hard limit at 124mph indicated at 5200 rpm in 5th. 124 mph is also 200 kph so I assume that’s where they limited it.

#5

Interesting. So the rev limiter for the stick IS cars is 6450? I will check the ECU. Thanks for the tip. How do you determine if it is a 525 or not and what number should I looking for?

#6

Stock redline for 153, 173, and 525 DMEs is 6350 RPM. I haven’t checked others, but assume all unmodified E30 DMEs to have the same limitation.

#7

Reference a speed limiter, cut the brown/red wire at Pin 29 on the DME connector to disable.

#8

Perhaps we are at 6350 rpm after all. That would help explain the difference between the ~122 mph indicated and 116 calculated. Regardless, it is the wrong time to focus on the dash when approaching the bus stop at Watkins Glen! That was the only point on the track where hitting the rev limiter became an issue. New car, so we need further adjustments on the kickdown link age.

NASA144 (thanks, Will) sourced a 4:10 LSD for us, so I’ll report back after the June LeMons race at Summit Point.

Here is a drive-by at the checkered flag:
http://youtu.be/DnE8RlOvN6U