Stick shift drag racers, clutch advise wanted

1wild-horse

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Got a new build put together last year, finished up dialing it in this spring. Quick details are full weight, 9.5:1 compression, .020 over, KB 2.0 @ 15 psi, custom cams, longtubes, E85, solid axle, 3.55 gears, T56 and a 26 spline.. running QTP Hoosiers trapped a best of [email protected] in the 1/8.
Went with a Vengeance clutch and was really impressed with feel and drivability out of the box as I broke it in with some short drives and a few trips to work. Car has never been on the dyno so power level I estimated to be around 600 with the passes its making.. went with the 750hp rated organic twin.
So... after a few nights and some tnt at the track, I would have to guess but, maybe 20 passes, it started stinking. Could smell hot clutch after a pass. This last trip out, got the car out of the trailer and headed to town for fuel. A good blip of the throttle and the clutch isn't holding. Pulled it out, and sure enough, the disks are smoked.
Took forever getting here, I know but here is the question:
What are the guys running the shit out their cars every weekend using for a clutch? The RXT seems like the go to, I just don't want to jack around with the pivot ball bullshit if I don't have to. Any other options?
 
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03' White Snake

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I’m making 820 hp 767 tq on my setup. The Spec 3+ handled the power fantastic. Street ability was crap. Clutch is an on/off switch. If you can figure out the sweet spot, it is not a bad clutch. My car is a street car, but I am not easy on it by any means. I make 2-3 track nights a yr on it.

I just installed the RXT 1200 HD in it. I have about 500 miles on it and just started getting on it a bit. Engagement is nice and smooth, holds the power. My 2 complaints with it,

1.) the pivot ball BS. I ground the shit out of the magnum case, shortened the stud 5mm and the clutch still releases near the end of stroke. Takes some getting used too for sure.

2.) I get some severe clutch vibrations / chatter in 4th gear 1500-2500 rpm, then it goes away. Sounds like a box of rocks are in the transmission. No other gear, load or anything does this. Only 4th gear for some reason. Never heard this with my spec clutch before.
 

DCguy

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1.) the pivot ball BS. I ground the shit out of the magnum case, shortened the stud 5mm and the clutch still releases near the end of stroke. Takes some getting used too for sure.

2.) I get some severe clutch vibrations / chatter in 4th gear 1500-2500 rpm, then it goes away. Sounds like a box of rocks are in the transmission. No other gear, load or anything does this. Only 4th gear for some reason. Never heard this with my spec clutch before.

No doubt the RXT's are great clutches. I had one in my OEM T56 and it worked well. But when I sold that and picked up a Magnum I did some research and found out what you've discovered....having to grind away at at the clutch fork / Magnum case to create the proper clearance etc.....the reason is due to the RXT's clutch stack height....especially with the Magnum this becomes a real problem. The release point being at the very top of pedal travel would be something I couldn't deal with.

I sold my replacement RXT I had sitting in the closet waiting to go in with the Magnum swap and will be trying out the Centerforce DYAD which is their version of a twin disk.....having seen both I can say that the DYAD has a lot more design features that I like over the RXT. It comes with a recessed billet steel flywheel so the overall stack height is much lower....so that fixes the clearance issues. Its also a sprung hub, unlike the RXT, which should keep chatter to a minimum. Lastly, for a drag car, there is also the DYAD XDS which trades in the organic disks for ceramic 6pucks for more grabbing power and firmer shifts......the puck style clutches can be hard on cranks though if you run large PD displacment blower setups so a crank stud or crank support would be a necessary addition here.

 

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