Dyno Test Review – SPEC Mini Twin-Disc Clutch Kit
By OR Staff
Like a good set of tires, drivetrain is an often-overlooked area of car tuning. Many obsess over blowers, exhausts and wheels but when it comes time to get that project buttoned up, the cheapest clutch kit is usually shoved in.
Or, more often than not, the stock clutch is pushed to the ragged edge and subjected to 400 lb/ft more torque than it was ever designed for.
Being cheap and getting too light of a clutch is a surefire way to shorten the life of your clutch kit and reduce the efficiency of your car. Besides having to live with poor pedal feel and the possibility that something will go wrong, meaning the transmission will have to be pulled again, using a cheap clutch can actually leave acceleration power on the table. Who wants that?
Remember, all the power in the world is a great thing but it still has to get to the pavement. To complement a high-powered engine, you’ll want a clutch kit that has more than enough holding power, good pedal feel (if driven on the street), smooth engagement and a lighter weight. With all these elements in place, a car can accelerate and decelerate faster using the same amount of power.
The key is the fact that the clutch and flywheel are solidly bolted to the engine’s crankshaft at all times. The clutch and flywheel combo will always spin around at the same RPM that your engine is reading. By pressing in the clutch pedal and moving the gear lever, you’re actually engaging and disengaging the transmission’s input into the engine.
16lbs lighter than stock
It’s simple enough to guess that a lighter clutch and flywheel is easier to spin up to a certain RPM since it weighs less. This is the reason for the massive popularity of lightweight aluminum flywheels; they can get you tenths in the quarter-mile with their reduction in weight.
And since the force required to spin a clutch depends on mass and clutch size, a smaller clutch should also aid with acceleration. It’s the same principle behind using lightweight forged wheels versus big, heavy chrome rims.
Taking rotating mass out of your drivetrain with carbon fiber driveshafts, lightweight clutches and small wheels has been done for years. But to find out how effective it really is we hit the four-wheel dyno at Tuning Technologies in Colton, California.
Alfred, Jen and the TT crew opened up their facility for us to test the SPEC Clutch Mini Twin kit on the M1 Fabrication & Development 2005 Mitsubishi Lancer Evolution VIII. This Evo has seen some heavy track use in NASA Time Trial competition and we decided to test the stock and SPEC clutches back to back. A custom GT30R turbo kit has been fitted to the M1 Evo VIII and 420whp is available at a low boost setting of 22psi.
The SPEC Mini Twin clutch kit offered both of the elements that we were looking to test gains from, a smaller size and a lighter weight. Rated to hold 800 lb/ft of torque, the SPEC clutch kit came with an aluminum flywheel 7lbs lighter than stock (8.5 versus 15.5 lbs) and was 16lbs lighter in total than all the factory parts. This is even counting the SPEC hydraulic throwout bearing that converts the clutch from a pull-type to a push-type for more reliable operation.
| Stock flywheel | Stock clutch/flywheel/pressure plate/throwout bearing | SPEC flywheel | SPEC Mini Twin kit w/hydraulic throwout bearing | |
| Weight (lbs) | 15.5 | 37.0 | 8.50 | 21.0 |
With aftermarket clutches there are a few ways to increase holding power and torque capacity but each have their downsides as well. Some of the most common include different friction material (better heat resistance but minimal holding power gains), a stronger pressure plate (stiffer pedal to push down) and swapping to multiple discs (expensive and could be noisy from internal rattling).
The SPEC Mini Twin clutch uses two clutch discs with what is basically another flywheel sandwiched between them. This gives more surface area than just one clutch and thus more holding power with minimal pedal stiffness.
Pedal feel with the SPEC twin-plate clutch is noticeably light and short and the engagement is much sharper than with the factory clutch. Without as much mass on the flywheel to help launch the car, this kit is designed for road racing and track use, not for drag racing.
The clutch needs to be slipped with plenty of revs to keep going and is pretty easy to stall. You get used to it and this unit can be used in a street car but it’s not exactly street friendly with an OEM feel. This is a real racing unit. SPEC does offer more street friendly units but this racing-style clutch is the best option for us to be able to test the difference in rotational mass.
First up, we dyno the GT30R’s fury against the stock clutch setup. This combo has overheated and slipped on track at Buttonwillow Raceway, proving the low capacity of the stock parts. Next, Tuning Technologies completed an amazing 4.5-hour clutch swap. That may seem really long to some of you but remember, this isn’t a Honda Civic. An Evo clutch install is an ordeal and could easily take twice as long.
The SPEC clutch was then given a full solid day of driving for break in and then the M1 Evo was put back on the same dyno. Both dyno runs used the same exact Tuning Technologies ECU tune and boost level. We measured the same exact atmospheric conditions except for a 2-degree F increase in air temp for the SPEC testing.
Dyno testing reveals the time difference required to reach a specific torque out put. The lighter SPEC system is faster past 3,000 rpm.
The results are eye opening, with the lighter and smaller SPEC twin-disc clutch kit allowing the Evo’s engine to rev faster and easier, hitting peak boost and making power sooner. Where the stock parts allow the Evo to reach 300 lb/ft of torque in about 5.2-seconds, the SPEC clutch hits that same amount in only 4.5-seconds. We measured almost a half second difference from stock for the Evo to reach the 350whp mark and once peak boost is reached, the SPEC clutch helps free up power all the way to the top.
It took almost an entire second less for this Evo to reach the 300 lb/ft mark during a single dyno run. Think about when this car goes out for a track session. Imagine how many times the car must enter braking zones, hit apexes and then accelerate out of a corner. Multiply all that acceleration by the time gained here and you’ll see the advantages of reducing rotating weight and having a lightweight clutch.
Races are won or lost by fractions of a second, we have that here already in a single dyno run and this clutch won’t slip at all on track. Sometimes going faster isn’t just about adding power. Sometimes it’s about maximizing what you already have.
Sources
Spec Clutch
(800) 828-4379
www.specclutch.com
Tuning Technologies
(909) 783-1200
www.tuningtechnologies.com
M1 Fabrication & Development
(714) 671-0077
www.m1fd.com
