Part of making big power is having the proper means of putting the power to the pavement. It goes without saying that a stock clutch isn’t going to handle making nearly three times more horsepower, but when it comes to clutches that can handle the power, drivability starts to become the gray area. That area can now look a little more blue thanks to Centerforce and their DYAD twin disk clutch technology.
Cameron Prause, the Southern California owner of this sweet ‘Stang, built the ride up to make sure that it’s performance matched its smooth looks. The 2006 GT’s 4.6-liter engine had previously been overhauled with a forged Cobra crankshaft, forged Manley H-beam connecting rods and pistons to make sure the internals were strong enough for the polished 2.6-liter Kenne Bell supercharger that would sit on top.
Complimenting the Kenne Bell installation were Ford Racing cams, an AFCO dual pass heat exchanger, 60 pound fuel injectors, GT500 fuel pump and American Racing long tubes. When all was completed and tuned, the end results were impressive to say the least. On an engine dyno, the modified V8 pounded out 650 peak horsepower and 610 ft-lb of torque.
This SoCal Stang was packing more power that it's updated clutch could handle. We found an easy solution using the DYAD dual disk clutch from Centerforce.
We first started building twin disc clutches in the 1980s, but the problem was, there wasn’t many street cars during this era that produced enough power to need a twin disk clutch.
When installed back in the Mustang, an aftermarket clutch was added to the otherwise stock drivetrain, but it wasn’t long after that when the troubles started. Getting power to the pavement depends on a number of components doing their job right, but just like a chain, it can only be as strong as the weakest link.
The Mustang runs a staggered tire setup, with 20 x 8-inch Bose forged alloy wheels in front and 10-inch wide versions out back. Shod with massive 285/30ZR20 BF Goodrich KDW tires, the back end was doing its part in getting the power through. Unfortunately, it wasn’t long before the single plate clutch began slipping on hard acceleration and something needed to be done.
The Dual Disk Phenomenon
Dual disk clutches first found application in the contemporary Shelby GT500. Previously reserved for use on ultra high performance vehicles, the benefits of the dual disc design apply equally to hard charging Mustangs. Offering higher torque handling capacity without an equal increase in pedal effort, the dual design also maintains smooth engagement and driver control. “We first started building twin disc clutches in the 1980s, but the problem was, there wasn’t many street cars during this era that produced enough power to need a twin disc clutch,” said Will Baty of Centerforce. “Now vehicles come with 400 horsepower from the factory and now weigh a lot more, so the demand resurfaced.”
The DYAD Clutch components include (L to R) the pressure plate, floating clutch disc, floater plate, drive clutch disc and flywheel. With the smaller diameter clutch components, the flywheel can be lightened with extra holes.
The design approach is rather simple, needing only a small increase in mechanical complexity to achieve these benefits. A standard, single plate clutch works by squeezing the clutch disc that is attached to the transmission, between the engine flywheel and the clutch’s pressure plate. The clutch disc has friction material on both sides and the ultimate torque handling capacity depends on that material plus the clamping force that can be generated by the pressure plate.
Getting more torque capacity is a balancing act of epic proportions and some pretty extreme measures have been taken in the past. Changing the friction material can yield better results, even to the extent of using sintered iron pads, but the impact on drivability is extreme. This is a competition-only solution. “When you are making over 500-600 horsepower, people should start considering a twin disc clutch,” explained Baty. “Most people don’t stop there and want to make even more power, and the DYAD will handle virtually anything you can throw at it.”
Increasing the contact area between the clutch disc and the flywheel is another approach, but physical limitations exist, so this can only go so far. Keeping the weight of rotating components low is a priority as well. If the clamping force is increased. typically by using stronger springs in the pressure plate, the pedal effort to release the clutch increases as well.
Pins on the driven clutch disc connect with the floating clutch disc, so that they turn as one, but can float up and down as the pressure plate engages.
We wanted to go with a positive drive floater type clutch system because it’s already a proven technology that we see in Top Fuel cars.
Once we throw away the idea of only being able to have one clutch disc, a whole new world of possibilities opens up. First, with two clutch discs, we now have four friction surfaces to work with. Clamping forces can be reduced since they are applied to four surfaces, so pedal effort no longer requires steroid injections in your left leg. “A single disc can hold the power in a lot of circumstances, they just don’t hold it for very long,” said Baty. ” With a twin disc, you have twice the material and surface area to distribute that power.”
The arrangement of components is only a little more complex, as shown in the diagram. The pressure plate is almost unchanged, except it is deeper to handle the extra clutch disc and floater plate. The two clutch discs are connected by drive pins and the floater plate sits between them. The drive pins allow the clutch discs to turn as one, but lets them move axially to release their grip and to accommodate disc wear. “We wanted to go with a positive drive floater type clutch system because it’s already a proven technology that we see in Top Fuel cars,” mentioned Baty.
Beyond all this, the overall clutch design can be more compact, using smaller diameter discs and components which reduce driveline inertia. The benefits just don’t stop coming.
• Fully dampened clutch system designed for vehicles with extreme power levels • Smooth engagement and light pedal effort • High torque capacity - 1300 lb/ft at the flywheel • All ARP fasteners • Specification dyno card included
If attention to detail was ever a question in your mind with a Centerforce clutch, then you would be happy to know that every DYAD clutch comes with a certificate that tests the clutch through a wide range of pressure tests before it is sent to you.
Application and Install Notes
For our install, we turned to the folks at Centerforce and their DYAD product which is well suited for this particular pony. With a limit of 1300 ft-lb flywheel torque, this clutch wasn’t about the be overwhelmed by the supercharged engine’s output.
The Arizona company has products for all Mustang modular motor applications since 1996. Both 6-bolt (cast) and 8-bolt (forged) crankshaft variants are covered on the 4.6-liter V8, as well as the 2006-2009 supercharged 5.4-liter GT500 engine and now the 2011+ 5.0-liter engine as well.
Installation, as we’ll see in the accompanying photos, is virtually no different than for a standard, single disc clutch and is a direct bolt-in replacement for the original clutch. No special modifications are required. Swing by the powerTV garage now as we perform a little clutch swapping exercise.
With the car up on a hoist, the first business at hand is to get the exhaust system out of the way. Remember to disconnect the oxygen sensor wiring before dropping the exhaust. If you're doing this job at home without a hoist, be sure to take all necessary safety precautions, including jack stands on all four corners of the car. As you can probably tell from Sean's face, the exhaust did provide us with a little bit of removal resistance.
The driveshaft is next to come out. The two-piece factory shaft has already been replaced with this one-piece aluminum shaft. The front end has already been removed from the transmission, which has a flanged input shaft, so you don't have to worry about fluid leakage.
An impact gun and socket extension will make removing the pinion flange bolts a lot easier. They are 12mm, 12-point bolts, so make sure you have the correct socket available. You can get these bolts out by hand, bit it will take some effort.
Before loosening the transmission crossmember, you'll want to have removed the bellhousing and starter bolts. A long extension (or two) and universal joint from your socket set will help a lot here. Be sure to support the transmission before removing the crossmember bolts.
With the transmission supported, you can slide it back carefully to remove. Take your time and get another set of hands if needed. You have to disengage the transmission input shaft from the flywheel pilot bearing before the front end will be free. A light hand here will avoid a bent input shaft.
Well, we got to this job just in time. As you can see. there's precious little left of the friction material on the previous clutch.
The flywheel isn't looking a lot better either. Luckily, we'll be replacing it with a new one. This forged Cobra crankshaft uses eight bolts to hold the flywheel, while a regular GT motor has six here.
Be sure to use some threadlocker on the new bolts when installing the replacement flywheel. They should be torqued down in a criss-cross fashion to avoid any possibility of warping.
Using the supplied alignment tool, the driven clutch disc is installed first. This is the one with a splined hub in the center.
Next, the floater is installed, making sure to align it with the spools on the flywheel. After that, the floating clutch disc goes on, connecting with the drive pins from the other clutch disc.
Now, the pressure plate can be installed and fastened to the flywheel. Again, use a torque wrench and multi-stage tightening in a criss-cross pattern to avoid misaligning or warping any of the parts. Getting the transmission back in will be about as challenging as getting it out, so take your time and fund some extra help if needed. Getting too brutish here could be quite unrewarding.
After putting the rest of the car back together, go back over all your work one more time to make sure you've left nothing out. Double check all wiring and mechanical connections before the key goes anywhere near the ignition switch. You'll almost certainly be glad you did.
This Pony is ready to rock. Getting power to the pavement will be a lot easier now, so long as the rest of your drivetrain is up to the job.
Results That Shout for Themselves
Short and simple, the first time out after break in with the new Centerforce DYAD clutch installed, getting that 610 ft-lb of torque past the clutch was no problem at all. “For breaking the clutch in, I recommend 500 normal and easy miles,” Baty recommends. “Try to keep away from full throttle runs. You don’t want to generate a lot of heat, but you want to seat that friction material in by bedding that material into all the metal surfaces in that clutch.” Unfortunately, passing that motive force through the stock transmission became the next challenge. As you’ll see in the photo, the transmission’s input shaft surrendered in a pretty spectacular fashion as a result.
Installing a high torque clutch can be helpful in finding the next weak link in the drivetrain. In this case, it was the input shaft on the factory transmission, which was never designed to handle the torque this engine was supplying.
Swapping that carnage out for a GT500 six-speed gearbox resolved the torque limit issue and a Powerhouse one-piece aluminum driveshaft looks after connecting the gearbox to the GT’s rear axle. All in all, this Mustang now delivers on the promise that its good looks make. The chatter that we previously experienced with the original clutch is completely gone, plus the need to have a strong left leg to push it the clutch pedal in is no longer needed.
Centerforce’s DYAD technology really does work. The twin disc design doubles the surface area available for the engine to transmit its power, which allows Centerforce to reduce the harshness of materials used; this is what makes this clutch last while harnessing tons of power. The drive lug design locks both clutch discs together and completely eliminates chatter and clutch noise. No longer was the clutch the weak link in this drivetrain and we paid the price of a broken input shaft when all the power was actually transmitted to the rear wheels.
It is a bit amazing that the Centerforce clutch can handle this amount of torque because it drives exactly like a stock Mustang - now your girlfriend can take it to work without the worrying about a cloud of clutch smoke following her. Looking to make more power down the road? No problem, this clutch will take it while laughing at you to bring more. An admirable balance of show and go have been built up and that makes this pony a smooth operator.