Building the Subaru VA WRX clutch and Flywheel with ACT!

Building the Subaru VA WRX clutch and Flywheel with ACT!

by Mike Kojima

All wheel drive cars are traditionally hard on clutches. With tons of traction, launches involve a lot of clutch slippage. Fast shifting and even downshifting are all harder on the clutch due to the increased traction of 4 wheels.  With this in mind building a daily driver heavy duty clutch for a street car is always a challenge. 

It just so happened that our friends at ACT were wrapping up development of a clutch and flywheel combination for the late model VA WRX when we were at their office and we thought it might be a good opportunity to show what is deep inside ACT's WRX clutch which shares many design features with all ACT clutches.

 

We will get into the construction of the ACT pressure plate in detail in a second.  It is a heavy duty part that has a clamping force of 2900 lbs, up from the stock WRX pressure plate clamping load of 1900 lbs.
The ACT WRX clutch disc uses a smooth engaging organic friction material with a high copper content for superior heat dissipation. This disc itself has stronger construction throughout to better stand up to the abuse of a daily driven modified vehicle.
The ACT Streetlite Flywheel is machined from a  4140 chromoly steel forging. 4140 is a very tough steel alloy with a high nickel content that imparts a lot of strength.  The flywheel is drilled to accommodate both the stock and ACT heavy duty pressure plates.  It weighs 13.7 lbs vs the stock 19.4 lbs.
Internally the ACT pressure plate uses a new diaphragm spring of their manufacture to get more clamping force. The diaphragm springs starts out with a spring steel blank. The blank is 20% thicker than the stock spring.

 

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