I am the one that engineered the mc²racing aluminum & polyurethane diff mount.

The diff mount is a tremendously important mount to upgrade, and it is often overlooked. On our autocross Merkur XR4Ti, we were having a lot of trouble with rear suspension deflections - which in our case was on the order of inches. We minimized this problem by installing a Group N (909) diff mount, and I have been a HUGE fan of the Group N diff mount ever since. Last year I wanted to pickup a second Group N diff mount, but when I went to order one from GGR I discovered that Ford had discontinued them! To the drawing board I went.

Now, I modeled the aluminum & polyurethane diff mount after the Group N diff mount. The critical dimensions are 100% identical, and the effective stiffness and NVH are identical. I went through several test bushings with a variety of different durometers and tolerances before selecting the one that is currently in production. I can say based on first-hand experience that you can not tell the difference between a vehicle equipped with a Group N diff mount and one of our diff mounts, which means that I accomplished my goal.

Of course, our diff mount has many advantages over the Group N diff mount since I don't have any bean counters watching over my shoulders like the Ford engineers do. Our mount is about half the weight, yet is quite beefy. Our mount is also cheaper. I paid $180 (£97.3 today) for my Group N diff mount 5 years ago, yet I sell our diff mount for $160 (£86.5 today). Finally, you can replace the bushings. When the Group N diff mount goes bad, it's bad forever. When our mount goes bad, you just stick in two fresh bushing "halves", which cost about $25 (£13.5 today) total.

We do have the solid diff mounts available also, but those are for cars that do not see street duty at all. If you ever drive your car on the street, use a polyurethane diff mount. If you never drive your car on the street, use a solid diff mount. It's that simple, and there are no exceptions.