Top Fuelers and NASCAR guys saw the light and began using multi-disc clutches decades ago. That’s because the design has a couple of very real advantages over single-disc clutches when it comes to competition. Namely, multi-disc clutches can hold more torque without slipping and can be smaller in diameter to reduce the driveline’s rotating weight. As a bonus, they also maintain an easy pedal despite being able to handle horsepower loads that would make activating a single-disc clutch feel like you are doing 300-pound single-leg presses at the gym.
These days, modern EFI computer controls combined with superchargers and turbos are making it easier than ever to build ridiculous horsepower in street cars that are both affordable and easy to drive every day. Or at least, it can be easy when it’s done right. That’s why multi-disc clutches—previously the domain of big-budget race teams—are now becoming quite popular in high-horsepower street cars.
In order to make any clutch handle more torque without slipping, you must do at least one of three things: increase the friction coefficient of the clutch material, increase the clamping force pushing the clutch face into the flywheel, or increase the surface area. With a traditional single-disc clutch, taking any of these factors too far comes with real drawbacks.
Make the friction material too strong and the clutch becomes an on/off switch, making it impossible to evenly release the clutch for smooth starts. If you increase the clamping force too high, you wind up with a heavy pedal that requires too much force to engage. Finally, increasing torque capacity by making the clutch a larger diameter not only makes the clutch heavier, but it also moves the weight farther from the center of rotation, increasing the moment of inertia so the car doesn’t accelerate as quickly. Plus, a larger diameter clutch also means the diaphragm spring grows at the same ratio, making the clutch pedal tougher to engage because the throwout bearing has less leverage.
A multi-disc clutch, however, avoids the pitfalls by spreading the load among two or more clutch discs and pressure plates. This increases the surface area where friction can be created between the discs and pressure plates, allowing the overall diameter to be smaller and the friction material more forgiving. The result is a clutch that can handle absolutely stupendous amounts of horsepower while also providing a “friendly” pedal with good feel without requiring Conan legs to engage.
That’s why Heintz Racing owner Jeff Heintz decided to go with a Mantic triple-disc clutch after adding several upgrades to a 2013 ZL1 Camaro. The ZL1 is already potent with 580 horsepower at the crank and around 490 at the rear wheels, but like all good horsepower freaks this car’s owner is a big believer in the “more is always better” philosophy. So Heintz has installed new CNC-cut cylinder heads, a bigger cam, a Magnuson Heartbeat supercharger and complete exhaust system, bringing horsepower at the rear wheels all the way up to 805.
That’s more than enough to put the power beyond the range of the twin-disc clutch that comes on the ZL1 from the factory. Heintz says he’s used Mantic triple-disc clutches on several similar builds with good success because he says the design handles big power and hard driving with no issues while the clutch pedal feels barely stiffer than stock.
Mantic clutches are manufactured in Australia and imported by Mantic Clutch USA. Mantic Clutch USA’s Technical Manager Geoff Gerko says the company has several clutch kits for most later model American muscle cars. The triple-disc clutch does require the design to be thicker, so the only requirement is to have enough input shaft length on the splined area to get the clutch assembly to fit.
Here, we show Heintz Racing’s installation of Mantic’s triple-disc 9000-series clutch and flywheel into the 2013 ZL1 Camaro we’ve already mentioned. But the process is similar for other makes and models of cars as well as multi-disc clutches from other manufacturers.
Modern cars are making it easier than ever to produce big power, but you’ve also got to make sure all that extra horsepower and torque can make it to the rear wheels efficiently.The Mantic clutch kit arrives in this ridiculously cool metal briefcase. We’re talking James Bond level cool. Everything is packed inside, including the new hydraulic throwout bearing which we’d already removed before this photo was taken. Obviously, a briefcase isn’t going to make your car faster, but we thought it was pretty neat.Here’s the reason the 2013 ZL1 Camaro needed a clutch upgrade. Jeff Heintz of Heintz racing says a stock ZL1 of this vintage will make around 490 horsepower at the rear wheels, but after adding new CNC-cut cylinder heads, a bigger cam, new Magnuson supercharger, and a full exhaust this Camaro was putting 805 to the ground.Heintz (left) and Bob Wilkinson (right) set to work pulling everything that has to come out just to get to the clutch. That includes the driveshaft, exhaust, transmission, and various heat shields and other silly stuff that clutters up modern cars.The stock clutch is already a twin-disc design, but it’s still not enough to handle the upgraded horsepower and torque levels for very long.Just for comparison’s sake, here’s a shot of the guts of the stock clutch and flywheel.This is Mantic’s lightweight billet steel flywheel. Before it can be bolted up to the crankshaft, you must slide the supplied cover bolts in from the back (engine side) because there won’t be clearance once the flywheel is bolted up.You won’t be able to reach the cover bolts easily once the flywheel is bolted to the engine, so a slot is machined into the back side of the flywheel to capture the head of each bolt so it cannot spin on you.The flywheel bolts are torqued to 75 lb-ft with a little Loctite just like Mantic suggests. From this angle you can see the protruding cover bolts and the mating surface for the first of the three clutch discs.Here’s one of the three clutch discs. Despite being able to hold over 1,500 lb-ft of torque at the crank, each disc is just 9 inches in diameter and uses a ceramic-based friction material. What impressed us is Mantic was still able to include sprung hubs which will help reduce chatter and improve overall ride quality.Between each clutch disc is a billet steel pressure plate (floater) that acts as a surface for the clutch discs to press against. The four spring fingers on the outer edge helps keep the clutch from hanging up by opening gaps between the pressure plates and clutch discs when the pedal is depressed.Every disc and pressure plate is labeled with the side that should face the flywheel. All you have to do is pay attention and you can be confident that all the components are correctly oriented and in the right order.A machined drive block slides over each cover bolt. They are designed to fit tight against a ridge on the flywheel so they won’t spin.After cleaning each of the pressure plates, all the components are assembled. Notice how a clutch disc sandwiches between each pressure plate. The clutch discs are splined to fit the transmission’s input shaft, while the pressure plates have notches on the outside edges that will lock into the drive blocks we showed you earlier. So the pressure plates are always spinning with the crankshaft and flywheel, while the clutch discs are locked to the transmission’s input shaft. Mantic includes a clutch alignment tool, but Heintz Racing uses a steel splined shaft pulled off a previous build.The alignment tool slides into the pilot bearing on the crankshaft and keeps all the discs and pressure plates properly aligned until the assembly can be bolted down. The nuts on the billet machined clutch cover are to be tightened in a star pattern a half turn at a time to keep everything even until finally torqued to 33 Nm (approximately 24 ft-lbs).A good way to ensure everything has seated properly is to make sure each of the diaphragm fingers are even. Mantic says that if there is a variation between the fingers of more than a millimeter, the clutch cover hasn’t been fitted correctly and should be retorqued.Here’s a better view of how the pressure plates lock in against the drive blocks.Wilkinson plumbs in the new hydraulic throwout bearing. Mantic’s Geoff Gerko actually pre-assembles each clutch pack and checks the compressed height to ensure it is within spec, so as long as you are using a stock bellhousing and throwout bearing you can be confident that you will have enough throwout bearing clearance.The new clutch is installed and ready to go. All that’s left is to reinstall the transmission and other components. For best results, a new clutch should be bedded in much like new brakes. Mantic recommends 500 miles of stop-and-go driving without doing anything crazy—or fun—like burnouts or hard launches. After that you are free to let ‘er rip.
