E30 M3 Rebuild: Differential
We began this project car with a clear focus on improving the performance of the suspension and the brakes, since the engine already had a thorough going over by another shop a few years back. The one speed area of the performance equation we decided to improve right from the start was changing the gear set in the differential. The biggest bang for the buck is not in adding power to the E30 engine, but changing how the exisiting power gets to the ground. This is espcially important at the track, where this car will consume most of its gas.
Speaking with many E30 M3 experts around the country, we settled on what was considered by almost everyone we spoke with as the best track driving gear ratio for the differential: 4.45. We had E30 expert-- and differential builder extraordinaire-- Ben Thongsai out of Chicago craft the new unit for us. He built up the diff with the aforementioned 4.45 gear-set, 4 clutch limited slip with 50% lock-up. We also had him install the M Coupe cover which has bigger cooling vanes, again with an eye to track use.
Hard to tell what this is, thanks to all the rust, dirt and oil, but here's the original differential still in the car:
Here we have the old one out, sitting next to the beautiful new unit:
A close-up showing the M Coupe cooling fins:
The new differential, installed:
