Project Professional Awesome Time Attack Evo: Part 4 – Drivetrain


In this close up you can see how the finishing process gets right into the root of the gear.
Mitsubishi included an access panel in Evo 4-9 5-speed transmissions that has a side job of assisting in lubricating 4th gear, which is a known weakness in Evos. TRE Transmission saw this access panel as a great opportunity to improve upon the design and also allow for the addition of an external oil cooler. We haven’t yet logged oil temps of our transmission, but we err on the side of weight savings by not running one as of yet. With the limited amount of fuel on board, the car can only run for 2-3 laps at full bore. For those turning more laps, this adapter can be a life saver.
So how does the TRE adapter improve oiling on 4th gear? We see here, in a disassembled transmission, that the access panel curves around this idler gear, which is always turning when the gearset is turning. It just so happens to be in line with 4th gear, so it has a side job of flinging oil in that general direction.
With the TRE adapter in place, the gap between the gear and what would now be the new panel, is greatly reduced and now acts as a ramp for the oil to move along the path of the gear. Furthermore, the gear in encapsulted on what was an open side previously, keeping the oil that is in contact with that gear captured. This greatly increases the amount of oil that rides on the gear and therefore, gets flung at 4th gear. The more oil that is flungĀ keeps the gear and oil in that area cooler.
Here’s what an overheated gear looks like from an Evo transmission. The Evo gears are on the narrow sideĀ and the way Evo owners beat on their cars, it’s no surprise the get overworked. Another issue is that the GL-4 fluid used in these transmissions can easily overheat and lose its effectiveness. Once the oil breaks down, the gears quickly overheat and start shearing teeth.

TRE gave our transmission their Stage 3, top level treatment. TRE builds the transmission for racing applications featuring gear detail work to the lead edge and root diameter of the gear teeth, which allows the gearsets to handle higher torque loads. The entire gearset receives high intensity shot peening to raise the ultimate strength of the gearset, increasing fatigue resistance, while also reducing gear wear. The oil passageways are enlarged to increase the flow of oil to critical parts and all critical surfaces are polished to a mirror-like finish. High rpm shifts are improved as the engagement teeth are modified to increase the window of opportunity. Smooth shifting is the result of REM Isotropic Superfinishing of the hubs/sleeves, shift rails and shift assembly. Afterwards the gearset is blue-printed to match the transmission case and assembled.


Here is our prepped transfer case, ready for install. You can see the oversized case cover bolts in the lower, right hand side of the photo. This better keeps everything in place. An interesting side note, the front differential resides in the transfer case on Evos, with the center differential residing in the transmission.

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