Project Legacy GT Part 2: Bolstering the Drivetrain
Finding the right balance of performance and civility when upgrading a street car can be difficult. It all comes down to finding the perfect compromise between daily drivability and “because racecar”. Go too far and a car can become too loud, too rough, and too unreliable. With the goal of eventually increasing the power output of our Subaru Legacy GT wagon beyond what the stock VF40 turbo can efficiently produce, we knew that we would need to upgrade some of the other components in preparation. Our clutch disc and pressure plate were the first items on the list of things to replace. While everything was apart for the clutch job we decided to also replace the heavy stock flywheel with a lightweight alternative, to bolster the transmission with help from Moore Performance, and reduce slop with some polyurethane bushings.
Even though a previous owner had put in a new stock clutch disc shortly before this car came into our lives, we knew that it wouldn’t be able to hold our eventual power goals without slipping. The stock clutch never gave any trouble with the power we were making with basic bolt ons, and always had smooth engagement with a pedal that was easy to modulate. These traits were something we wanted to maintain in our street car, so a Competition Clutch “Stage 2” clutch kit was chosen. The kit includes everything we needed to replace the clutch: a new disc, pressure plate (with hardware), pilot bearing, throw out bearing, and an alignment tool. The disc is a solid full faced organic disc with their Brass Plus material and a sprung steel hub, which should give great longevity with smooth engagement. This disc is rated to be able to hold 450 ft lbs of torque at the wheels when paired with their pressure plate (which isn’t just some re-sprung OEM plate), and should be more than adequate for street duty with some occasional track day abuse.
For the 2005 and 2006 model year Legacy GT, Subaru decided to use a chunky dual mass flywheel which weighs 27.8 pounds. Some people choose to update to the single mass flywheel which comes on the 2007+ models and weighs in at 23.6 pounds. We decided to go straight to an aftermarket lightweight flywheel, and managed to reduce our flywheel weight by a little more than half.
Our Competition Clutch kit also came with their SFI approved machined 4140 forged steel flywheel which weighs a meager 13.7 pounds. There are lighter flywheel options available that feature more machining around the outer edge, and this would free up more power and allow the engine to rev more quickly, but at the risk of making the throttle difficult to modulate smoothly in traffic. We played it safe and didn’t go for the most feather weight option out there, and have zero complaints about street drivability so far!