Tilton Clutch
Posted: Wed Apr 26, 2006 11:06 pm
Earlier this evening I was on the phone with a Tilton engineer about how to fit a Tilton clutch to my Northstar. I had pretty much decided on a 7.25" unit before I talked to him. I just wanted to sort out PP load & ratio, # disks and friction material.
He said there are two characteristics that define the limits of a clutch: torque capacity and heat capacity.
Torque capacity is obvious.
As far as heat capacity goes, the smaller and lighter the clutch the less heat it can absorb before its temperature rises to damaging levels. Therefore the smaller and lighter the clutch, the less it can be slipped.
Tilton offers three friction materials: sintered iron for road racing, cerametallic for rally and a setup with one organic disk and one cerametallic disk for street use.
The major factor affecting the modulability of the clutch is the compressibility of the disk. Marcel in a conventional street clutch spreads the engagement load over a wider range of engagement travel than flat disks. Tilton disks are not available with Marcel. The organic friction material is more compressible than the other two, which is why it is the most streetable. It also has the lowest grip and lowest heat tolerance.
The cerametallic and organic disks are significantly thicker than the sintered iron disks. The result is that a two disk cerametallic packages in the same setup height as a three disk sintered iron.
On a scale of 0-10 for modulability, 0 being a light switch and 10 being an OE street clutch, the sintered iron is about a 2 and a cerametallic is about a 4. A carbon-carbon clutch is about an 8, but I don't have the money for that, so I'm going to pretend it doesn't exist for the sake of my sanity.
We settled on the 2 disk cerametallic for my application. He spec'd the 66-302UORA pressure plate. This is an ultra-high ratio (lighter pedal effort than merely high ratio) unit with 600 ftlb capacity (not the softest, but on the softer side of what they offer).
Page:
http://tiltonracing.com/product/7-25-in ... ng-clutch/
Installation drawing:
http://tiltonracing.com/wp-content/uplo ... I-7.25.pdf
Installation instructions:
http://tiltonracing.com/wp-content/uplo ... Clutch.pdf
For the 282 with 25mm x 14 spline, he suggested the 64185-7-AA-12 disks. The -12 at the end is the code for that particular spline.
Page:
http://www.tiltonracing.com/content.php ... &id=83&m=d
Installation instructions:
http://www.tiltonracing.com/pdfs/36.pdf
Measuring from my somewhat worn Centerfarce I have 2.25" of total engaged stack height. Wtih 1.37" of engaged stack height on a new Tilton, I have 0.88" in which to package a N* flexplate and a button to bolt the clutch to. I think I can do that, but I need to look at the flex plate a little more closely as I believe it has some contours that will get in the way.
The Tilton has a max throw of 0.250", but when new should be fully disengaged with 0.160" throw. Disengagement load will be about 500#. Tilton runs a 1.2 sqin piston area hydraulic TOB with 3/4" diameter (0.44 sqin) for a hydraulic ratio of 2.7:1. When used with a 5-6.5:1 pedal, this results in 13.6 - 17.7 overal ratios, or pedal loads of 28.3 - 36.8 lbs. I'll have to run the numbers with the Fiero clutch mechanism to see what I can come up with. Does anyone know the MC and various slave cylinder diameters right off?
The clutch can tolerate a total of about 0.030 of wear in all the friction components before requiring new disks and steels. Since the diaphragm spring in the ultra-high ratio pressure plates operates at a 5:1 ratio, this will mean 0.150 additional stack height at the TOB, so the throw out mechanism needs to be able to tolerate a clutch height of 1.52"... which feeds back into acceptable button thickness, which has dropped to 0.73".
The diaphragm fingers require a radiused face TOB. The ideal contact diameter is 44mm, but they can be used with up to 50 mm. Throw out bearing remains to be figured out, but I'll probably send him a spare that I have so that he can come up with a good match for it.
I will eventually convert to the hydraulic throw out used in the later 282's, but for now the setup has to work with the mechanical throw out mechanism.
Based on experience with his 1st gen RX7, he estimates that I could see 40K miles on the clutch if I hone my technique to make sure that it's fully engaged within a carlength or so from a dead stop. Drag strip use will be harder on it, but he said heat is the big enemy for that and the clutch will be fine if I give it time to cool between runs.
Oh yeah, the unit weighs 8.2# or so. With the flex plate and button, the total weight for the whole shebang should be less thant he stock flywheel by itself (14#).
He said there are two characteristics that define the limits of a clutch: torque capacity and heat capacity.
Torque capacity is obvious.
As far as heat capacity goes, the smaller and lighter the clutch the less heat it can absorb before its temperature rises to damaging levels. Therefore the smaller and lighter the clutch, the less it can be slipped.
Tilton offers three friction materials: sintered iron for road racing, cerametallic for rally and a setup with one organic disk and one cerametallic disk for street use.
The major factor affecting the modulability of the clutch is the compressibility of the disk. Marcel in a conventional street clutch spreads the engagement load over a wider range of engagement travel than flat disks. Tilton disks are not available with Marcel. The organic friction material is more compressible than the other two, which is why it is the most streetable. It also has the lowest grip and lowest heat tolerance.
The cerametallic and organic disks are significantly thicker than the sintered iron disks. The result is that a two disk cerametallic packages in the same setup height as a three disk sintered iron.
On a scale of 0-10 for modulability, 0 being a light switch and 10 being an OE street clutch, the sintered iron is about a 2 and a cerametallic is about a 4. A carbon-carbon clutch is about an 8, but I don't have the money for that, so I'm going to pretend it doesn't exist for the sake of my sanity.
We settled on the 2 disk cerametallic for my application. He spec'd the 66-302UORA pressure plate. This is an ultra-high ratio (lighter pedal effort than merely high ratio) unit with 600 ftlb capacity (not the softest, but on the softer side of what they offer).
Page:
http://tiltonracing.com/product/7-25-in ... ng-clutch/
Installation drawing:
http://tiltonracing.com/wp-content/uplo ... I-7.25.pdf
Installation instructions:
http://tiltonracing.com/wp-content/uplo ... Clutch.pdf
For the 282 with 25mm x 14 spline, he suggested the 64185-7-AA-12 disks. The -12 at the end is the code for that particular spline.
Page:
http://www.tiltonracing.com/content.php ... &id=83&m=d
Installation instructions:
http://www.tiltonracing.com/pdfs/36.pdf
Measuring from my somewhat worn Centerfarce I have 2.25" of total engaged stack height. Wtih 1.37" of engaged stack height on a new Tilton, I have 0.88" in which to package a N* flexplate and a button to bolt the clutch to. I think I can do that, but I need to look at the flex plate a little more closely as I believe it has some contours that will get in the way.
The Tilton has a max throw of 0.250", but when new should be fully disengaged with 0.160" throw. Disengagement load will be about 500#. Tilton runs a 1.2 sqin piston area hydraulic TOB with 3/4" diameter (0.44 sqin) for a hydraulic ratio of 2.7:1. When used with a 5-6.5:1 pedal, this results in 13.6 - 17.7 overal ratios, or pedal loads of 28.3 - 36.8 lbs. I'll have to run the numbers with the Fiero clutch mechanism to see what I can come up with. Does anyone know the MC and various slave cylinder diameters right off?
The clutch can tolerate a total of about 0.030 of wear in all the friction components before requiring new disks and steels. Since the diaphragm spring in the ultra-high ratio pressure plates operates at a 5:1 ratio, this will mean 0.150 additional stack height at the TOB, so the throw out mechanism needs to be able to tolerate a clutch height of 1.52"... which feeds back into acceptable button thickness, which has dropped to 0.73".
The diaphragm fingers require a radiused face TOB. The ideal contact diameter is 44mm, but they can be used with up to 50 mm. Throw out bearing remains to be figured out, but I'll probably send him a spare that I have so that he can come up with a good match for it.
I will eventually convert to the hydraulic throw out used in the later 282's, but for now the setup has to work with the mechanical throw out mechanism.
Based on experience with his 1st gen RX7, he estimates that I could see 40K miles on the clutch if I hone my technique to make sure that it's fully engaged within a carlength or so from a dead stop. Drag strip use will be harder on it, but he said heat is the big enemy for that and the clutch will be fine if I give it time to cool between runs.
Oh yeah, the unit weighs 8.2# or so. With the flex plate and button, the total weight for the whole shebang should be less thant he stock flywheel by itself (14#).