Project Legacy GT Part 2: Bolstering the Drivetrain

by Connor Harrison

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.


The Competition Clutch Stage 2 kit is an excellent performance upgrade capable of holding 450 ft lbs of torque while maintaining a nearly stock feel with smooth drivability.

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.


The factory dual mass flywheel is a real porker.

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.


Prior to installation, make sure to clean off all the oil from the flywheel to allow for proper clutch break in conditions.

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!


The OEM flywheel looks massive beside the lightweight Competition Clutch. This angle makes the aftermarket flywheel seem shallow by comparison, but I assure you it isn’t.
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Scott Helmer
Scott Helmerlink
Monday, December 21, 2015 10:05 PM
As a two time previous Subaru owner and lifelong Subaru enthusiast, I must say a couple things:

1 - Those blast plates are an absolutely tremendous idea, and I'm glad somebody came up with them!

2 - Ahhhh, good old "Uncle Scott's Tranny Blend" (the name always stuck for me for fairly obvious reasons). I never got the opportunity to try it, but the results I saw online were always very positive, and I wholeheartedly recommend it to anybody that owns a 5 speed Subaru. Seriously, it's a fantastic mix, almost a shame nobody sells it in a prepackaged container to take the guesswork out for the shadetree mechanic (not that it bothers me, but I'm sure there are those out there that are wary of trying to mix their own fluids).

Awesome article, keep 'em coming!
Dan DeRosia
Dan DeRosialink
Tuesday, December 22, 2015 5:48 AM
I'm interested in how the blast plates actually do. As owner of a bugeye with fairly modest power goals, I'd much rather swap in the V6 STI 5-speed I have with some reinforcements rather than shell out for everything needed to do a 6-speed swap properly. I'm not sure if the theory is sound, but I want it to work.
Connor Harrison
Connor Harrisonlink
Tuesday, December 22, 2015 8:51 AM
@Dan DeRosia, there seems to be a lot of back and forth debate about the effectiveness of these blast plates. The Legacy should end up around 400whp when its finished, so nothing crazy for power to push the limit, but it seemed like a reasonable idea to try and keep our gears together.
Dan DeRosia
Dan DeRosialink
Tuesday, December 22, 2015 9:35 AM
Yeah; I know a lot of people have done a lot of analysis but everyone has their axe to grind. I'm shooting for about 400whp myself (albeit at less torque) on what's basically the same gearset.
Tuesday, December 22, 2015 12:33 PM
Any rear diff reinforcement planned? I swear mine (04 WRX with stock power these days, 107k miles) moves around all over the place even with Perrin "rear lock down" kit. The diff bushings themselves are probably a bit shot though.
Tuesday, December 22, 2015 12:52 PM
And with that thought, I just ordered Turn In Concepts rear differential bushings hahaha.

Also Uncle Scotty's Cocktail is excellent, I use it for every transmission fluid change. Such an improvement in cold synchro engagement, especially 1st gear.
Tuesday, December 22, 2015 2:43 PM
I bet those chemical engineers that came up with each respective fluid are pissed. They spend countless hours perfecting their formula and all these stupid kids are mixing their fluids with other crap with who knows whats in it all cause some guy on a forum says his tranny grinds less...

but seriously, I'm curious what they think of this, haha
Tuesday, December 22, 2015 3:02 PM
Is that Spotted Cow I see lurking in the foreground there of the fluids shot?
Connor Harrison
Connor Harrisonlink
Tuesday, December 22, 2015 3:08 PM
Good eye, Tom!
Dan DeRosia
Dan DeRosialink
Tuesday, December 22, 2015 3:47 PM
warmmilk: The argument goes that the Subaru transaxle has the 3 issues of sharing insufficient gear tooth area for its loads, synchros, and a hypoid gear all in the same fluid. In theory off the shelf fluids alone aren't optimized for all 3 of those at once, but by mixing several you can get a good compromise.

I'm not sure I agree but that's the theory.
Tuesday, December 22, 2015 8:02 PM
Looking at how and where the blast plates mount, is the problem twisting of the case (not the case flexing outward), or is the problem bending of the bearing bulkhead between the two bolts in each bulkhead?
All 4 of the plate mounting points are bolts that go through the shaft support (split) bulkheads, and there are already through-bolts there so the blast plates aren't adding any extra clamp load to the bulkhead halves. Is the problem that the bulkheads are twisting with respect to each other? This would imply that the blast plates are tie plates at the bolt ends (similar to how a crank girdle works with bearing caps), limiting the relative motion of the bulkheads. A torsion problem would explain why the plate is so heavily stiffened between the bulkheads, because the jog in the plate wouldn't add much stiffness if the problem was the individual bulkheads spreading apart between the bolts and bearings. I can envision the mid bulkhead maybe spreading apart because of the large bolt spacing, but the way the blast plate is made it doesn't seem to fit with the directions of the loads if that were happening.
I'm very curious about how the flex was actually measured and characterized under load (was a driveline dyno involved, for example?), or whether assumptions were made about the failure mode and then FEA was performed based on that...? I'm just a skeptic when it comes to things like this, but maybe the explanation of how it works is just very vague and I'm trying to infer too much?
Wednesday, December 23, 2015 12:00 PM
but whats to say that certain chemicals in the 4 different fluids don't get canceled out or have some sort of other negative affect when combined...
but I'm no chemical engineer, so I'm not sure how this works... I'm mostly curious what the people that worked on each respective fluid think of people mixing them together with other stuff...
Dan DeRosia
Dan DeRosialink
Wednesday, December 23, 2015 12:39 PM
What's to say they don't cancel each other out or have negative effects together? Not much other than "well, it seems to work". I think there's been some testing by enthusiasts doing this stuff to figure out if stuff is blatantly incompatible or not, but I'm not 100% sure what to think of, for example, Shockproof. I've heard people in the business of doing gears that have gone at LeMans say it's basically useless, for example, but I dunno.

I honestly kinda dislike the cocktail idea, in the sense that it seems like there really should be a better solution. But then it seems to work, so...
Wednesday, December 23, 2015 12:56 PM
Ahhh.... owning a Subaru, Your tools will never get dusty. So many companies have made themselves rich by offering products that fix the weaknesses from the factory.
I remember those days....Thanks for the memories!
Monday, December 28, 2015 3:00 PM
$400 for some 3/16th plate and square tube welded up? Wow.

Well I at least know of a cheap project I can knock out the next time the rally car transmission is out.
Tuesday, December 20, 2016 5:58 AM
Any update to your legacy Connor?
I have been waiting a year with my Legacy to see what you did next.
Don't leave a brother hanging.
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