This is a post to help you know which differential is in your car. The stamping on the top of the casing tells all. These are the numbers of teeth on the ring and pinion. Divide the two and you’ll have the rear axle ratio.
Sprites work great with every ratio. 4:22 is the stock axle ratio you’ll find in most bugeyes. Starting with Mark III Sprites and Mark II Midgets, a 3.9 rear axle ratio became optional, which is better on the highway, and with the 1275 Engine you lose a little off-the-line acceleration, but the 1275 can support a lower ratio because of additional horsepower.
After 1975, a 3.7 differential was used in the 1500 midgets, and some people like that for the additional reduction, but a five speed transmission is really the best way to improve your highway cruising RPMs… in fact, the reduction in RPMs from the five speed is much greater than a reduction from changing the rear axle ratio. The optimal set-up seems to be a 3.9 Diff with a five speed but there’s nothing wrong with a 4:22 and a five speed as well, because you keep great acceleration at hand, but drop the RPMs in fifth gear when that’s desired.
We can pretty easily provide a five speed transmission kit for our clients (whether we build it here or send you a kit). Differentials are a little harder. Most of the differentials now are starting to whine due to wear and it’s difficult to properly clearance them and rebuild them with new bearings. We do sell the bearings and also the gear sets if you have a rebuilder that can assemble it properly for you, or you can hire us to do that as well.
Give a call if you’re interested! Or keep your existing differential, and buy one of our five speed’s below!
