What Gives?: Twin Disc Systems by the numbers
Feb 7, 2005, 12:36 PM
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What Gives?: Twin Disc Systems by the numbers
Since the release of the Evolution VIII to U.S. market, owners looking for a long-term replacement clutch for high power applications have been choosing the market leading Exedy Twin Disc. This clutch, whose discs are available in a cerametallic and also a carbon-ceramic (semi-carbon) compound, has been great for daily-drivers and highly modded EVO’s alike. More and more customers are coming back with damaged Exedy Twins with a simple question…WHAT GIVES?
Twin Disc clutch systems employ eight surfaces that transfer torque from flywheel to transmission. The surfaces are as follows; two surfaces on each of two discs, one on the flywheel, one on the pressure plate casting, and two on the intermediate friction plate that sandwiches between the discs. In an Exedy Twin, four of these surfaces are single-piece steel (all but the discs themselves). Examining the steel friction components from several damaged units gives reason. High RPM engagements create enough heat to alter both the surface hardness (Rockwell) and overall shape of these steel components. Increased Rockwell on portions of steel is similar to a patch of ice on the road, when the disc material contacts it skips right over until it grips on the next softer piece of steel causing chatter and excessive wear on the disc. As for the steel plate changing shape (have seen up to .039”)…this is when the clutch becomes useless at transferring any significant amounts of power, having a surface warp eliminates over 90% of the contact area making friction co-efficient nearly impossible. Warped friction plates also add thickness to the whole assembly which cuts down on the clearance required to disengage the clutch, making the car almost impossible to shift. Exedy has been good about replacing these components with no issue, but owners are forced to foot the bill for labor to have these parts replaced.
***the following measurements are from a 400 WHP evo that had completed over 10,000 miles of street and occasional track use***
Since the problem found us, we have been looking for a worthy replacement clutch. A clutch that uses design principles that are suited for the high-heat, high-RPM abuse that most EVO drivers dish out trying to transfer large amounts of power to the ground in a matter of seconds. Enter the RPS twin-carbon. Using True-Carbon (not carbon-metallic) segments on all friction components does a lot for EVO drivers. The simple fact that friction is created using the same carbon material on both sides ensures the same co-efficient, so heat build up will be the same on both sides. Having the carbon segmented (separate pieces) stops heat from transferring around the surface, eliminating the possibility of warp found with one-piece designs. In addition, the friction coefficient of carbon increases with heat, so more heat= more stick. To top off the list of RPS benefits, the overall diameter (Exedy-7.93” vs. RPS-9.6”) and surface area (Exedy 28”sq. vs. RPS 43.1”sq.) of each friction surface are greater than that of the Exedy and others, creating a leverage advantage that requires less friction to transfer the same amount of torque. Our “hard core” racer clients are using carbon-carbon technology to do 2nd gear burnouts, 2nd gear launches, and even line lock assisted launches with the clutch semi-disengaged to load the engine to make positive boost (15~30 psi) in 2nd gear!!! Others do 1st gear, 7000+ RPM clutch dumps controlling traction by slipping the clutch for a fraction of a second. No matter how you abuse it, C-C technology has shown to provide smooth, chatter-free engagements for many thousands of miles regardless of how much power your car has.
Owners have argued the RPS carbon costs too much. Well, any EVO owner who is willing to pay $1500 plus labor for a non-carbon aftermarket clutch system should weigh the issue: paying roughly $1000 more for C-C technology needed to launch my car over and over without failure. Considering that most installers are charging between $500 and $800 for labor, having to pay for component replacement one time with a standard twin-disc would make the C-C investment an instant payoff.
For owners who realize the need for C-C technology, your decision will not be disappointing.
Twin Disc clutch systems employ eight surfaces that transfer torque from flywheel to transmission. The surfaces are as follows; two surfaces on each of two discs, one on the flywheel, one on the pressure plate casting, and two on the intermediate friction plate that sandwiches between the discs. In an Exedy Twin, four of these surfaces are single-piece steel (all but the discs themselves). Examining the steel friction components from several damaged units gives reason. High RPM engagements create enough heat to alter both the surface hardness (Rockwell) and overall shape of these steel components. Increased Rockwell on portions of steel is similar to a patch of ice on the road, when the disc material contacts it skips right over until it grips on the next softer piece of steel causing chatter and excessive wear on the disc. As for the steel plate changing shape (have seen up to .039”)…this is when the clutch becomes useless at transferring any significant amounts of power, having a surface warp eliminates over 90% of the contact area making friction co-efficient nearly impossible. Warped friction plates also add thickness to the whole assembly which cuts down on the clearance required to disengage the clutch, making the car almost impossible to shift. Exedy has been good about replacing these components with no issue, but owners are forced to foot the bill for labor to have these parts replaced.
***the following measurements are from a 400 WHP evo that had completed over 10,000 miles of street and occasional track use***
Since the problem found us, we have been looking for a worthy replacement clutch. A clutch that uses design principles that are suited for the high-heat, high-RPM abuse that most EVO drivers dish out trying to transfer large amounts of power to the ground in a matter of seconds. Enter the RPS twin-carbon. Using True-Carbon (not carbon-metallic) segments on all friction components does a lot for EVO drivers. The simple fact that friction is created using the same carbon material on both sides ensures the same co-efficient, so heat build up will be the same on both sides. Having the carbon segmented (separate pieces) stops heat from transferring around the surface, eliminating the possibility of warp found with one-piece designs. In addition, the friction coefficient of carbon increases with heat, so more heat= more stick. To top off the list of RPS benefits, the overall diameter (Exedy-7.93” vs. RPS-9.6”) and surface area (Exedy 28”sq. vs. RPS 43.1”sq.) of each friction surface are greater than that of the Exedy and others, creating a leverage advantage that requires less friction to transfer the same amount of torque. Our “hard core” racer clients are using carbon-carbon technology to do 2nd gear burnouts, 2nd gear launches, and even line lock assisted launches with the clutch semi-disengaged to load the engine to make positive boost (15~30 psi) in 2nd gear!!! Others do 1st gear, 7000+ RPM clutch dumps controlling traction by slipping the clutch for a fraction of a second. No matter how you abuse it, C-C technology has shown to provide smooth, chatter-free engagements for many thousands of miles regardless of how much power your car has.
Owners have argued the RPS carbon costs too much. Well, any EVO owner who is willing to pay $1500 plus labor for a non-carbon aftermarket clutch system should weigh the issue: paying roughly $1000 more for C-C technology needed to launch my car over and over without failure. Considering that most installers are charging between $500 and $800 for labor, having to pay for component replacement one time with a standard twin-disc would make the C-C investment an instant payoff.
For owners who realize the need for C-C technology, your decision will not be disappointing.
Last edited by LogicPerformanc; Feb 7, 2005 at 08:43 PM.
Feb 7, 2005, 12:49 PM
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Wow, good reading!
What about the reports of the RPS C-C wearing out much faster than the Exedy twin? Is it true about the true carbon being a bit more "fragile" when it comes to wearing down, over the semi-carbon?
What about the reports of the RPS C-C wearing out much faster than the Exedy twin? Is it true about the true carbon being a bit more "fragile" when it comes to wearing down, over the semi-carbon?
Feb 7, 2005, 12:52 PM
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I bet Exedy loves this type of advertising from one of there dealers. 
That plate looks like somebody did not install/adjust the clutch correctly or was riding the clutch everywhere they went.
That plate looks like somebody did not install/adjust the clutch correctly or was riding the clutch everywhere they went.
Feb 7, 2005, 01:01 PM
#4
I have an exedy twin disc clutch in my evo at this current time that is exhibiting the non-shift symptoms. I am wondering what Exedy plans to do about this as I have some measurement tools of my own. The clutch was run for about 2 wks and made about 7 passes at the strip where it failed. There is also a cost associated with removal and replacement.
Sean
Sean
Feb 7, 2005, 01:07 PM
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Originally Posted by jj_008
I bet Exedy loves this type of advertising from one of there dealers.
That plate looks like somebody did not install/adjust the clutch correctly or was riding the clutch everywhere they went.
That plate looks like somebody did not install/adjust the clutch correctly or was riding the clutch everywhere they went.
The twin discs are having issues. Dont know exactly what it is yet, but you can rule out inproper installation on most cases. And for the most part, improper installation too.
Brian
Feb 7, 2005, 01:08 PM
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Originally Posted by Sean I
I have an exedy twin disc clutch in my evo at this current time that is exhibiting the non-shift symptoms. I am wondering what Exedy plans to do about this as I have some measurement tools of my own. The clutch was run for about 2 wks and made about 7 passes at the strip where it failed. There is also a cost associated with removal and replacement.
Sean
Sean
Chris
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Feb 7, 2005, 01:15 PM
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Originally Posted by TURBODAWG
There is no adjustment on the clutch itself. Just the clutch pedal freeplay and upper stop (which is the upper clutch switch). Hydraulic clutches are self adjusting, all you can do is adjust the rod length to make it engage/disengage sooner/later in the clutch travel.
Feb 7, 2005, 01:24 PM
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Originally Posted by Sean I
the evo was at 400 wheel hp
The problem is the floaters warp very quickly as they have nothing to transfer the heat to. (And they are thin to begine with)
The adjustment was attempted that isn't the issue here.
Sean
The problem is the floaters warp very quickly as they have nothing to transfer the heat to. (And they are thin to begine with)
The adjustment was attempted that isn't the issue here.
Sean
Feb 7, 2005, 01:35 PM
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wow very good read....
I have to link this to my friend who is running the exedy clutch... I drove his car the other day and it chattered (he said it was normal)
I have to link this to my friend who is running the exedy clutch... I drove his car the other day and it chattered (he said it was normal)
Feb 7, 2005, 02:23 PM
#12
Heeeere we go again.... I seem to remember somebody else bagging the Exedy line, with NO solid information. In fact Exedy was still waithing to see the "failed" clutch back for inspection... Regardless...
To me this looks like RPS propaganda. I personally don't know many online retailers that own Rockwell Testers and do this type of testing in house.
I have a few questions regarding the "apples vs. apples" comparison in this "research". Why are you using a picture of the Pressure Plate Casting where the disc contacts and compare it with the Flywheel of the RPS setup? On a side note - if you compare Flywheels - the Exedy is half the weight of the RPS flywheel (which is a hunk of Steel that has been turned down) where Exedy’s is a Chrome-Moly forged flywheel. Point being - you're not comparing apples with apples.
As for the size comparison of the discs, the reason Exedy has smaller discs is to attain a lower inertia on the discs. A lower inertia results in quicker shifting. Exedy achieves more than half the inertia compared to the RPS clutch discs.
The technology RPS uses is primitive - No company like AP Racing, Tilton or ATS (or any reputable carbon clutch manufacturer) uses this type of technology.
In fact are you aware, RPS is so far behind the manufacturing curve - they use the Exedy OEM Replacement Stock cover in their setup. So any attempt to degrade the Exedy product would in fact reflect on the RPS as well. On this note, the reason the RPS clutch is larger in diameter, heavier, and primative is because they don’t have a clutch cover that they manufacture for their setup. They use – as stated – the standard Exedy OEM Cover.
Total approx. weight of RPS setup is 48lbs (Flywheel, Cover and Discs) the Exedy Carbon Twin Plate setup is only 21.25 lbs. – Over HALF the weight... you do the math.
If people are concerned of square inches of surface friction areas, they have the option of using the Exedy Triple Plate, which will increase the total friction area considerably.
Further, Exedy has non-public photos of *failed* RPS Carbon's which, never even made it if the Dyno, let alone to the level of "2nd Gear Burnouts". But due to Exedy’s policy, they will not give me them for posting at this stage.
Be careful of what you believe on the Internet - I think most "retailers" have motives, the more I read this – the more it sounds like an RPS ad.
-Matt
Refer to www.ExedyUSA.com for information on their product – and to get a better apples to apples comparison.
To me this looks like RPS propaganda. I personally don't know many online retailers that own Rockwell Testers and do this type of testing in house.
I have a few questions regarding the "apples vs. apples" comparison in this "research". Why are you using a picture of the Pressure Plate Casting where the disc contacts and compare it with the Flywheel of the RPS setup? On a side note - if you compare Flywheels - the Exedy is half the weight of the RPS flywheel (which is a hunk of Steel that has been turned down) where Exedy’s is a Chrome-Moly forged flywheel. Point being - you're not comparing apples with apples.
As for the size comparison of the discs, the reason Exedy has smaller discs is to attain a lower inertia on the discs. A lower inertia results in quicker shifting. Exedy achieves more than half the inertia compared to the RPS clutch discs.
The technology RPS uses is primitive - No company like AP Racing, Tilton or ATS (or any reputable carbon clutch manufacturer) uses this type of technology.
In fact are you aware, RPS is so far behind the manufacturing curve - they use the Exedy OEM Replacement Stock cover in their setup. So any attempt to degrade the Exedy product would in fact reflect on the RPS as well. On this note, the reason the RPS clutch is larger in diameter, heavier, and primative is because they don’t have a clutch cover that they manufacture for their setup. They use – as stated – the standard Exedy OEM Cover.
Total approx. weight of RPS setup is 48lbs (Flywheel, Cover and Discs) the Exedy Carbon Twin Plate setup is only 21.25 lbs. – Over HALF the weight... you do the math.
If people are concerned of square inches of surface friction areas, they have the option of using the Exedy Triple Plate, which will increase the total friction area considerably.
Further, Exedy has non-public photos of *failed* RPS Carbon's which, never even made it if the Dyno, let alone to the level of "2nd Gear Burnouts". But due to Exedy’s policy, they will not give me them for posting at this stage.
Be careful of what you believe on the Internet - I think most "retailers" have motives, the more I read this – the more it sounds like an RPS ad.
-Matt
Refer to www.ExedyUSA.com for information on their product – and to get a better apples to apples comparison.
Last edited by MattGold; Feb 7, 2005 at 02:30 PM.
Feb 7, 2005, 02:24 PM
#13
Originally Posted by EVO MR
wow very good read....
I have to link this to my friend who is running the exedy clutch... I drove his car the other day and it chattered (he said it was normal)
I have to link this to my friend who is running the exedy clutch... I drove his car the other day and it chattered (he said it was normal)
-M
Feb 7, 2005, 02:30 PM
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Originally Posted by MattGold
If people are concerned of square inches of surface friction areas, they have the option of using the Exedy Triple Plate, which will increase the total friction area considerably.
Chris