Project Professional Awesome Time Attack Evo: Part 4 – Drivetrain


Since a triple disc wasn’t needed for our power level, we wanted to switch to a twin disc to save weight. Exedy makes a wonderful, off the shelf, twin disc that works extremely well, but has a sprung hub meant to improve street drivability. I owned this exact clutch for years when the Evo VII was a true street car and loved it. The sprung hub makes it so easy to drive that even my mom had no issues wheeling the Evo around and pulling lengths on the pesky F-bodies and Mustangs that inhabit the Midwest. That being said, the sprung hub is added weight on the discs that can potentially slow down shifts, so Exedy combined the best of both worlds for us. The solid discs from the triple, but in a twin disc body. They even machined holes into the flywheel to further reduce weight and inertia. The twin has a capacity of 615 wheel torques, plenty for our needs and with room to spare, especially considering the car never sees aggressive launches.


Our transmission, transfer case and rear differential ready to go. TRE Transmissions is the premier Evo transmission specialist in the world in this author’s not-so-humble opinion. Not only is the work on the drivetrain components incredible, they look the part with all the aluminum cases being glass beaded and steel/iron parts being painted.

The transmission is a standard Evo VIII unit that has been thoroughly gone over by the best in the business, Jon Ripple at TRE (Team RIP) Transmissions. We’re lucky enough to live within driving range of this mechanical magician and if you get the opportunity to chat with him, you’ll learn more about a transmission than you can imagine even existed. First the basics. The gearing is completely Evo VIII with the addition of a JDM short-ratio 5th gear. The final drive is a 4:1 MFactory unit. The gear ratios (and approximate top speed per gear with our 295/30-18 tires) are 2.928:1 first (50 mph), 1.950:1 second (75 mph), 1.407:1 third (102 mph), 1.031:1 fourth (143 mph), and .825:1 fifth (179 mph).


The completed transmission ready to go. Here you can also see the TRE Transmission Cooler Adapter, which I will get into more detail below.
Here’s an example of a ring and pinion that have been REM Isotropic Superfinished. The process removes peaks and valleys in the gears’ surface finish to reduce friction, keeping the drivetrain components cooler and reducing wear. This is critically important in a transmission, such as ours, that is being pushed well above and beyond its designed torque capacity.
The surface finish is not unlike the WPC treatment MotoIQ readers are familiar with. The “non-directional Micro-texture” facilitates lubrication. The surface can be polished to a mirror finish, such as the lead shot to this article that has team member, Mike Lewin, holding parts finished for display. The mirror finish parts don’t tend to stay as well lubricated, so the milkier looking finish seen here is prefered for actual usage.

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