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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Tuesday, July 05, 2016 6:07 AM
I'm not sure if i can recommend ACT anymore. So about 6 years ago i installed a clutch kit of them on a Nissan CA18DET engine. HD pressure plate and 6-puck sprung cerametallic disc. After 6 months of operation i had disengagement problems. Turns out the bottom fulcrum wire ring yielded so the diaphragm and the rivets holding it came loose. I replaced it with a new identical one and after 6 months it had the exact same failure. I installed the stock pressure plate (god knows how old is now) keeping the same cerametallic disc and after 6 years it still holds just fine. I still don't know why the wire ring failed and neither ACT. They told me to ship them back the pressure plates but being on the other side of the globe is not cost effective since they didn't even promise a replacement..
Tuesday, July 05, 2016 9:42 AM
Seems like a GR WRX is shown?
Mike Kojima
Mike Kojimalink
Tuesday, July 05, 2016 11:39 AM
On the other hand my race car has an ACT clutch and it has been in the car since 1999 and has outlasted 3 engines!
Tuesday, July 05, 2016 5:37 PM
Does that extra 1000lbs of clamp force transfer to the same amount of additional pressure on the engine thrust bearing? I've always been weary of heavy pressure plates for that reason. Is it something to be worried about?
Mike Kojima
Mike Kojimalink
Tuesday, July 05, 2016 6:02 PM
The load at the disc is way less than at the crank.
Wednesday, July 06, 2016 4:39 PM
This is not a VA WRX
Wednesday, July 06, 2016 6:41 PM
This fits 2006-2016 WRX, VA included.
Friday, July 08, 2016 11:08 AM
The same clutch works for both the EJ25 (06-14 WRX) and the FA20 (2015+ WRX)? Interesting. The VA is the 2015+.
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