Differential Change from A 3.46 to A 2.93 -- Intended & Unintended Consequences

[PaleMelanesian]

Ok, that's cool. I'm envious of your gears now. If you continue the math, I'm at 2500 rpm at 60 mph and 3000 at 70 - BAD for mileage.

[jimepting]

Originally Posted by Shawn D.

Y'all,

For the time being, the 2.93 will stay in, but I'll probably change it back to the 3.46 for the autocross season. Yeah, I know autocrossing ain't "eco," but it sure is fun!

-Shawn
SIZE]

Good to see another automotive competitor. I also autocrossed many years ago. Went on to racing old 2002's and from there to Miata now. Autocrossing and racing are great fun

At the races we changed those 2002 diffs in about 30 minutes. BMW has a great setup for diff changes.

[tjts1]

I took my 91 318i (M42) from the stock 4.10 diff down to a 3.64. It make the car much more enjoyable to drive on the street because there was less shifting required and quieter on the highway. What I didn't expect is it became quicker to 60 (no more 2-3 shift) and actually more fun to autoX because I never run into the rev limiter or have to use 3rd gear anymore. With a 7200rpm limit, second gear can get me to almost 65mph. I think its the ideal ratio for this car although I wouldn't mind a 3.73LSD either.
Stock as it left the factory


As I have it now with slightly shorter 195/60 autoX tires. The graph doesn't go far enough but with a chip it revs to 7200rpm now.

[Shawn D.]

Originally Posted by tjts1

... it became quicker to 60 (no more 2-3 shift) and actually more fun to autoX because I never run into the rev limiter or have to use 3rd gear anymore.

That's a great result. With the 3.46, I can stay in 2nd during an autocross, but if I left the 2.93 in, I'd have to shift down to 1st.

[tjts1]

Hehe, it must be nice having some torque to play with. With the 1.8 engine I can't avoid down shifting to first in slow corners. That said, I managed second out of 13 cars in GS at my last autoX. It was a fast 'drift' course so I spent the whole time in second gear mostly out of control desperately trying to avoid the cones. Quick E36 rack without a PS pump was a handful but I can't wait to do it again.

Still managed 33mpg on the way home.