Tilton Racing Clutch
The next stage of assembly has been the installation of a rare-as-hens-teeth Tilton Carbon-Carbon Clutch.
This carbon/carbon clutch was a Tilton catalogue item for the MR2 Rev2 and GT-Four/Alltrac but was discontinued in 2006 due to low demand. I originally tried to get hold of a new one around that time but they only had a sintered version left. Eventually a secondhand carbon version came up for sale. This was one of a batch of Tilton carbon clutches originally imported into the UK by a group of MR2/GT-Four enthusiasts. A detailed description of the unit and the development background was published on a US web site a few years ago. It's quite an interesting read so I've reproduced sections of it below:
Tilton Twin Carbon Disc Clutches - The Miracle Clutch
Tilton were the first company to develop a carbon-carbon clutch to win in Formula 1, the 1987 Detroit Grand Prix, with Ayrton Senna's Lotus 99T Honda Turbo. Apparently this was the last GP victory for Team Lotus.
The Tilton clutch redefines clutch technology in various ways. The units use of lightweight material, weight set to the centre of the crank and its carbon on carbon construction are major advances.
Tilton also includes a few different size pressure plates to compensate for the wear on the discs and floaters. A graph and wear gauge are provided with the clutch to determine when a new pressure plate is needed. The drive hub is a unique piece that is patented by Tilton. Since the discs are made of carbon, the hub is a floater design rather than a rivet-style set-up.
Taking advantage of lightweight material is a necessity especially in four-cylinder applications. Many have tinkered with various ceramics and iron materials to improve clutch engagement and these efforts have been successful to some degree. The downfall of this approach is unavoidable; it is simply how a limited amount of surface area affects the heat resistance property of the clutch. Excess heat sacrifices holding power. Tilton addressed two fronts with its clutch-using twin discs to increase surface area and using exotic materials for added heat resistance. Tilton decided to use a lightweight carbon material for the following reasons; it's lighter than most other materials and has better wear properties, the clutch cover and pressure plate are made of aluminium, adding to the lightness as well as increasing the strength of the clutch assembly. Unlike most flywheels the Tilton chrome-moly flywheel has no friction contact patch for the drive plates (discs) to ride on. The unit relies on three floater plates to make contact with the number two-drive plate rather having the carbon contact the chrome moly surface. This not only improves the wear properties of the clutch but it also saves time when servicing the clutch. The starter ring gear is also machined into the unit and added perforations aid in cooling of the clutch while reducing weight. The 4140-chrome-moly flywheel is also heat-treated to endure extreme temperatures.
At each step of development the weight of the carbon composite material, the titanium clutch cover and all other materials were considered. Tilton's Carbon/Carbon clutches are available in 185mm diameter which is much smaller than a typical single-disc unit which measures in at 221mm. The smaller size has an effect on an engine's moment of inertia in comparison to an OEM unit. The rotating mass is narrowed down to the centre of the crank which allows the engine rev up more freely. The lighter load that the engine has to rotate is not only less than the OEM unit because of the lightweight material used, its moment of inertia is changed due to remaining weight of the clutch being so close to the centre of the crank. The weight of a single-disc clutch and OEM flywheel on a Honda B series engine is 29.8 lbs. The total weight of the Tilton unit is 12.6 lbs-the difference in these figures make it plain to see the advantages of the Tilton set-up.
Friction material and friction area are also critical concerns when dealing with high-horsepower applications. In the past, and present, different types of material have been used to transfer horsepower to the ground. Along with material concerns the size of clutch disc contact points (i.e. four puck, six puck and full face discs) are important factors. With the Carbon/Carbon unit Tilton relied on carbon composite to provide the necessary clamping force to transfer stratospheric power to the ground. What's different from most single-disc units is the use of a full carbon on carbon contact surface. With most single-disc units, the difference in disc material versus flywheel and pressure plate material tends to distort and cause uneven wear to all the parts. Since the Tilton's floaters and discs are constructed of carbon they share the same heat properties and, in turn, generate an even wear pattern while providing plenty of hook and book force. Even the chrome-moly flywheel and pressure plate becomes a non-friction contact patch due to the two additional floater plates the discs ride on.
The three floater discs are also of carbon construction making the unit a carbon-on-carbon design. This use of common material also increases the unit's heat resistance properties which is advantageous to performance and durability. Machined in the aluminum clutch cover are the posts the floater plates will ride on. This helps strengthen the clutch as a whole assembly.
One of the best features the clutch has to offer is its surface area coverage. A conventional clutch assembly has two sides of contact, one on the flywheel and one on the pressure plate with the disc in the middle. A twin-disc unit relies on two discs allowing for four areas of contact. This requires use of a floater plate to obtain the additional two surface areas. By bumping up on the surface area of the drive plates they are able to take on more horsepower and torque in the long run. With the two discs sandwiching the drive hub rather than two separate hubs riveted to the disc has made the clutch a full floating disc unit.
Until now it has been a foregone conclusion that a hardcore race clutch cannot be tamed for the street. Excessive chatter, poor initial engagement and pedal pressures that require a pry bar for engagement combined with the threat of stop-and-go traffic have made the streetable race clutch a mirage of the mind. Until now. High horsepower street machines can harness their power more efficiently with the Tilton Carbon/Carbon clutch. The full-face configuration of the carbon discs, their lack of pads and the result reduction of spring pressure need for engagement take the chatter out of the Tilton clutch. The full face design and light weight of the disc also dispatch abrupt engagement of the clutch. Furthermore, Tilton has moved the fulcrum point on the pressure plate to reduce pedal pressure and enhance the streetability of the clutch. If you have a turbo Honda or other power packed turbo-enhanced street machine and go through clutches quicker than you change your oil, the Tilton unit may be an install it and forget it proposition.
Since the Tilton clutch has enhanced the moment of inertia by virtue of its lighter weight and improved centre of velocity, technically it should not only hook up better but show a gain in horsepower output. Here are some pics of the unit as it was assembled into my standard ST205 gearbox.
Lightweight Racing Flywheel
Carbon Clutch Pack
Hydraulic Clutch Release Bearing
Assembled Engine/Gearbox/Transaxle unit offered up to the chassis
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