Project Professional Awesome Time Attack Evo: Part 4 – Drivetrain


Here you can also see the added billet TRE inspection cover magnet. The stock stamped steel inspection cover is replaced with this new cover that includes a high strength, neodymium trash magnet. This holds on to any steel that may have found its way into the oil, reducing wear and tear on our rotating parts.

As with the transmission, TRE completely worked over our transfer case. First everything is disassembled and hot tanked, clean enough to eat your veggies off of. A Magnaflux inspection is done on the ring and pinion gears, front differential housing and front differential gearset. Like the gearset on the transmission, there is gear detail work done to the ring and pinion to reduce stress risers and to increase strength for higher torque loads. The transfer case main and tail housings receive CNC machine work to ensure they are square to one another. The reason it is important to make certain that both housings are square to one another is because it has a profound effect on the ring and pinion contact pattern and overall durability of the transfer case. The side cover is also CNC machined for larger M10 bolts to more securely hold everything in place. The ring and pinion gear is shot peened and finished with REM Isotropic Superfinishing.

Our long-lasting Wavetrac front differential resides inside the transfer case as well. This differential has been through war and back. This was the same differential in the Evo VII when it was smashed into the wall at Road Atlanta. The transfer case was destroyed and one stub shaft became permanently attached to the Wavetrac, requiring the differential to be sent back home so the technicians at Wavetrac could separate the two parts. The differential survived with a few broken parts and was rebuilt and has continued to perform perfectly. What makes the Wavetrac special is that it works super smoothly, like an OEM Torsen differential, but with an additional locking feature if one wheel overcomes the torque bias ratio, which would normally split all the torque to the wheel with the least traction.


The rear differential didn’t escape TRE’s special touch. First thing to notice is the modified rear cover. A sight glass has been added to ensure the differential receives just the right amount of oil, which is a little higher than OEM. The factory differential is an 8 plate clutch type design and many have noticed that not all 8 plates are engaged from the factory. TRE improves upon Mitsubishi’s design by using 12 plates, a necessity for high power, high traction Evos such as ours.

Back we go to the rear differential. TRE works their magic here much like the transmission and transfer case. The most important change is switching to a 12 friction disc, MAX-LOCK upgrade. Given the greater grip that the rear tires can produce, the ability for stronger locking of the rear differential is a requirement to keep proper balance of the car in on throttle situations. We go a bit against the grain by choosing a 1-way differential, which only locks on accel, not under decel or coasting situations. This allows the car to be looser under braking and initial turn-in. The car is extremely stable in general, so we didn’t feel the need to induce additional stability via the differential being set up as a 1.5 or 2-way design. As with the other gears, the ring and pinion and spider gearset are shot peened and REM Isotropic Superfinished.


Also added is TRE’s heavy duty side cover. This replaces the OEM iron differential case cover and improves upon the design in many ways.
The factory part is cast iron, which is quite soft, and can be crushed, allowing the bearing to spin on the cover’s post. This allows the ring gear to wander both axially and radially in the direction that thurst is put upon it.
This wandering leads to noisy rear ends, due to excessive backlash and it alters the ring and pinion contact pattern, which can lead to gear breakage. The Professional Awesome team generally frowns upon gear breakage.

Additionally, we have a TRE Heavy Duty side cover which is CNC machined from billet 4340-CR steel. This choice of steel is much tougher than the OEM cast iron, with more material in critical areas and larger corner radii making the side cover very stout. This increased rigidity eliminates deflection of the factory differential housing, keeping the ring & pinion gear running perpendicular to one another, even in the harsh environment of racing.

There you have it, all the details of the Professional Awesome Evo’s drivetrain for the world to read. Please feel free to ask any questions you migh have below!



Exedy Racing Clutch

TRE Transmissions

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