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I've made several custom clutches for use in my high output stroker engines, in an attempt to make the "perfect clutch". The "perfect clutch" for high torque engines is one that will hold any amount of power you can throw at it and be perfectly smooth.
Tough to do.
The stock dual disc clutch is inadequate...even when it has increased diaphragm pressure and high friction clutch discs. These clutches are limited to ~400 ft.lbs. And if you abuse it once....it's all over. You need new pieces.
Spec clutches? An economical alternative, but the ones for high torque are difficult to drive. Ample amounts of chatter come in every box.
I came close with my carbon/carbon clutch. But not "perfect". These clutches will hold any amount of torque I can throw at them, but are a bit "finicky". The "release point" is very narrow and they need to be driven very carefully. You release the clutch too quickly and you will get chatter. Slow, precise, and consistent. Really tough to do every single time.
Because of this, I've been somewhat "clutch limited" and moved from building 6.5 liter engines for manual transmission cars to building 5.8 liter engines....just to remove some of the low end/mid range torque and move the power up in the rpm range. The 5.8 liter development has been fantastic...and suddenly we find ourselves "clutch limited" with those engines.
And then I "found" myself in an interesting position. I am "freshening" Andy's 605hp, over 500 ft lbs of torque 6.5 liter engine, and installing it into a 5 speed GTS. Track toy, for sure....but it needs to be driven completely smoothly from the owner's residence to the track. Sorry, can't do that. How about an automatic?
Interestingly enough, we had Jim Corenman's engine apart for a mysterious thrust bearing failure (yes, on a 5 speed!) Jim had about 40,000 miles on my carbon/carbon clutch and the chatter had increased (flaw in disc design.) Jim had noticed that Tilton had just brought out a dual disc 9.625" street clutch (ST-246), with a target market of hot rod Mustangs, Camaros, Corvettes, etc. Designed to hold 800 ft. lbs with organic discs and 1200 ft lbs with ceramic discs. And the organic version had Marcels....with spring center discs!
Can you say "smooth"? How about "potentially perfect"?
And, it appeared that it might actually fit inside a Porsche 928 bell housing! And it was incredibly cheap....$1250 for a complete dual disc clutch, including a flywheel for the "American" application you were going to use it on (the flywheel was junk, for us.)
Long story short:
A few months of designing, a bunch of measuring, a pattern or two (Jim Corenman), a scan of a late model bell housing (Rob Edwards), a bit of computer magic to overlay the pieces onto a crankshaft (Jim and Rob), a prototype custom flywheel (me), a custom input shaft to fit the Tilton discs (me), a bit of magic on the "push" T/O bearing (me), a little bit of change to the ST-246 assembly (Tilton), and we have the absolute perfect clutch!
Absolutely smoother than any stock clutch, can't remotely begin to make it slip with any of my engines. You can literally start off in 3rd gear from a stop. You can stop and drive up any incline. 3 pounds lighter than a stock GTS clutch assembly and flywheel.
Perfection, at last!
Because the custom flywheel, the custom T/O bearing, the custom input shaft are a bit pricey to make, the complete assemblies are not cheap....~$4500. The good news: If you ever wear it out (good luck with that!), the entire replacement clutch assembly is about 1/2 the price of a stock GTS pressure plate (currently only available from Porsche.)
The bad news: I made six units for testing and to satisfy my own immediate needs. Two left, at this time.
The really good news:
I have a single disc version of this in testing, to replace the stock 1985-1995 clutch and flywheel assembly. Most of the stock clutch/flywheel pieces are in very short supply and available from Porsche, only. A stock replacement flywheel, pressure plate, clutch disc, and clutch shaft is now over $3000.
From what I can tell, this single disc version will "hold" over 400 ft. lbs, but it is 12 pounds lighter than a stock GTS clutch. The single disc version will not be incredibly cheaper. ~$4,000. However, it will be able to use the pre-'89 bell housing in single disc configuration. It can also be "upgraded" at any time to the dual disc version, should your torque be increased (future proofing.)
You can ´t replace the Stock Dual Disc clutch with this? 85 to 95 is a little Bit confusing.
BTW, looks fantastic!
Yes, that was confusing.
To be specific, the dual disc clutch requires the "late" bell housing (model year 1989-1995, I believe), which has the T/O bearing mount moved back.
The single disc version will fit into the '85 to '88 bell housing. The '85/'86 version will require a different flywheel (different crank trigger, unless it has been updated to the later style injection, which I frequently do), which I have not made, as of yet. (I'll make this flywheel in the next batch of flywheels I have made.)
Truthfully, I haven't even considered the early Dual Disc clutches. I'll need to check the bell housings to make sure there is adequate room. Since those flywheels do not require a crank trigger, they will definitely be a bit cheaper to make....and lighter than the flywheels that require the trigger.
Jim really worked especially hard on this. His original idea. I had no idea that Tilton was building an economical clutch to compete with Quartermaster, Mcleod, etc. He also has the first prototype in his car and has driven it about 2,000 miles.
He's happy. And since it's Sue's car, she's really happy. The pedal pressure is very close to what their stock GTS has and the car is now super easy to drive.
It should be noted that the later single disk clutch used in the 85+ cars is marginal at best. When I had the Black Widow a stock 89S4 5 speed that put down 300whp-torque it had a new clutch installed by the original builder who did only 1 track day on it. When I pulled the engine for rod bearing repair the clutch was almost gone...this took precisely 9.5 hours on track....using redline shifts on R comp tires (335's)...my answer back then as a cost saving measure was the increased pressure plate as a stop gap....
The stock dual disk in Casper (1979) worked great at 265whp-280 torque for the 26 hours on track I had it, other than snapping the clutch shaft (which of course Doc makes out of the stronger steel too).
This is definitely going to find a home in my supercharged 81.
Originally Posted by GregBBRD
Truthfully, I haven't even considered the early Dual Disc clutches. I'll need to check the bell housings to make sure there is adequate room. Since those flywheels do not require a crank trigger, they will definitely be a bit cheaper to make....and lighter than the flywheels that require the trigger.
FWIW I have an 85/86 manual flywheel with the 100 tooth timing ring in my otherwise stock 81. I drilled a hole in the upper bell-housing and Todd made me a mount to hold the sensor. No clearance issues.
This really is a sweet clutch. The Tilton popped up on our radar a few months ago, about the time the carbon clutch gave it up entirely. The big question is whether it would fit, it would be annoying to have some very special parts made and then find out that it was a too big. But fit it did.
Here is the master at work... He's got work-benches, he's got chairs and stools, so what does he do??
And here it is, in place:
We've got about 2200 miles on it so far, much of it on I-5 but also stuck in Seattle traffic, creeping up-hill to a stop-sign, things that are all hateful with a bitchy clutch.
It should be noted that the later single disk clutch used in the 85+ cars is marginal at best. When I had the Black Widow a stock 89S4 5 speed that put down 300whp-torque it had a new clutch installed by the original builder who did only 1 track day on it. When I pulled the engine for rod bearing repair the clutch was almost gone...this took precisely 9.5 hours on track....using redline shifts on R comp tires (335's)...my answer back then as a cost saving measure was the increased pressure plate as a stop gap....
The stock dual disk in Casper (1979) worked great at 265whp-280 torque for the 26 hours on track I had it, other than snapping the clutch shaft (which of course Doc makes out of the stronger steel too).
Yet another amazing product from Doc.....
When the magazine writer "blew up" Van's clutch (literally broke the intermediate plate in half) I had to come up with a new clutch. Truthfully, the "old" dual disc, with a stiffer diaphragm had always been marginal....like if you abused it at all, it would slip. Used a dual disc unit (new flywheel, new intermediate plate, new pressure plate) with some high friction discs. Slipped as soon as the torque came up....any gear. Had a new pressure plate sent out to modify for increased pressure. They changed the fulcrum point, but left the diaphragm alone. Had them make 2 Kevlar discs, which they insisted would hold more torque. Drove it like an old lady (to break in the discs) for 100 miles. Then stepped on it. Slipped as soon as the torque came up.....any gear. I then install the same clutch pieces with the "high friction discs". Slipped as soon as the torque came up....any gear. I then took it apart....again. Installed two new stock clutch discs. It now works (clutch was in and out 5 times), but feels like it would slip if it was beaten on, at all. Luckily, Van is a great driver, uses the car, but doesn't beat on it, at all. He keeps idiots out of the car, now.
I'm hoping we can put one of these clutches in his car, it would be a great addition. I've got one set to the side, for him.
This really is a sweet clutch. The Tilton popped up on our radar a few months ago, about the time the carbon clutch gave it up entirely. The big question is whether it would fit, it would be annoying to have some very special parts made and then find out that it was a too big. But fit it did.
Here is the master at work... He's got work-benches, he's got chairs and stools, so what does he do??
And here it is, in place:
We've got about 2200 miles on it so far, much of it on I-5 but also stuck in Seattle traffic, creeping up-hill to a stop-sign, things that are all hateful with a bitchy clutch.
Thank you Greg!!
Thanks for coming up with the idea...and spending hours figuring out if it would fit...and spending hours working with me on the flywheel design.
By all rights, this should be called the "Corenman Clutch!"
Can you show everyone the "pattern" you made?
I love the fact that with the age of this car , things still progress forward.
Actually, it's not like I have a choice on some of the things I build. I'm forced to "create" pieces to keep moving forward.
I've got a new intake system, very close to being completed, which adds 100hp to a 6.5 liter engine with a stock style manifold.
I'm working on a new 1.875" 12 degree collector, equal length header system that should add 75-100 horsepower to Andy's engine.
Really needed a smooth clutch that can hold more power than I can pass through it.
Thanks for coming up with the idea...and spending hours figuring out if it would fit...and spending hours working with me on the flywheel design.
By all rights, this should be called the "Corenman Clutch!"
Can you show everyone the "pattern" you made?
There were actually three: The first was "old school", print the installation drawing at full-scale and see if it fits:
That looked good, but paper-pasted-onto-plywood isn't metal... I then did some 3D modeling, I'll dig those out and post them.
I wonder if that new shaft would work with what Simard came up with for using Tilson TO bearings and disks and pressure places. He made a Flywheel that would accept. Wonder if they are made for similar disks, etc.
12-17-2019, 04:02 PM
Finally. A perfect clutch!
