The big mods for the 2021 season are the differentials – specifically, the front and rear differential. This had been planned for the 2020 season, but the crash I had at the end of 2019 ruled that out.
The more significant upgrade is the front differential. The stock helical differential is okay, but not ideal for racing. For racing, it seems that clutch-type differentials are always superior for performance and lock-up. People who have done this modification claim it transforms the front end of the car – which makes sense compared to the helical. The car should be able to enter corners better with less entry understeer, and the car should also be able to power out of corners better, really pulling the car out. I’m curious to see if the effect will be as significant as has been claimed. I decided to go with the 1-way front carbon-hybrid, which uses carbon infused plates to allow for a higher initial torque without sacrificing drivability. I was recommended to go with the 1.5-way for braking/straight-line stability, but given the center and rear differentials, I decided to go with the 1-way to avoid any potential entry binding understeer. The front tires may lock up a little bit more, but with the Brembos and advanced electronic brake-force distribution and ABS, I don’t think this is going to be a big issue. The rear differential and center diff should provide enough braking stability.
As for the rear differential, well, the third time’s the charm? The Cusco 1.5 Type RS differential I had I think was too aggressive, feeling practically locked as soon as I touched the gas. The OS Giken 1.5-way was the opposite, feeling like it didn’t really do anything. I had TRE tweak the differential to be more aggressive, but even after, it didn’t feel like it was doing as much as I wanted it to, unless I got the car really out of shape. To be fair, with the big grip in the rear, I haven’t experienced a ton of power oversteer. I’m hoping the ATS will be a goldilocks option, allowing for good throttle adjustability and power oversteer when I need it.
Both these differentials cost a LOT of money – and I’m hoping their performance will justify the price. I’ll be breaking the diffs in during the early part of the season with figure 8’s and autocross, before giving it a shot at a track day.