7.5” vs 5.5” Clutch Assemblies

[Rick Iverson]

Gents;

Close to the point where I will send my engine to my builder for freshening. I have two clutch assemblies: A Tilton 7.25” single disc; and a 5.5” Quarter Master single disc.

Craig Taylor explained it to me this way: say you have a round metal disc 8” OD and of sufficient length to weigh 50 pounds. And you also have a metal rod 0.25” OD and at a length that weighs 50 pounds as well. Say you spin them at 60 RPM. If you needed to stop each one by hand, which would be easier?

I get it about the acceleration/deceleration pluses of the 5.5”, but the Tilton definitely looks beefier. What are the arguments of one vs the other as a function of rebuild costs, longevity, and performance pluses/minuses.

[DaveW]

I used a 5.5 single-disk QM clutch on my Pinto FC for years. I actually found it more robust than the 7.25". The reason was that the 7.25 always cracked between the segments and the 5.5 didn't.

Also, I had no issues with wear, but I was extremely careful with not slipping the clutch excessively driving around the paddock. I used the clutch for every shift, up or down, and even that didn't cause any wear issues.

So as long as you don't slip it excessively around the paddock or on starts, I'd think the 5.5 would be an advantage and not cause you any issues.

[Bob Wright]

It begs to ask...This is a FC (Pinto?). Back in the dark ages we used either a 7.25 single or a 5.5 twin plate. The 5.5 was considered superior because of the center of gravity. Could you get away with a single 5.5? It depends on the torque of the motor, but I don't remember ever seeing one used. If you have a current rules Pinto, it will have a lot of HP and probably needs one of the two I referenced above.

Your engine builder should have an opinion.

[Rick Iverson]

It begs to ask...This is a FC (Pinto?). Back in the dark ages we used either a 7.25 single or a 5.5 twin plate. The 5.5 was considered superior because of the center of gravity. Could you get away with a single 5.5? It depends on the torque of the motor, but I don't remember ever seeing one used. If you have a current rules Pinto, it will have a lot of HP and probably needs one of the two I referenced above.

Your engine builder should have an opinion.

Pinto

[DaveW]

It begs to ask...This is a FC (Pinto?). Back in the dark ages we used either a 7.25 single or a 5.5 twin plate. The 5.5 was considered superior because of the center of gravity. Could you get away with a single 5.5? It depends on the torque of the motor, but I don't remember ever seeing one used. If you have a current rules Pinto, it will have a lot of HP and probably needs one of the two I referenced above.

Your engine builder should have an opinion.

Mine was a single disk 5.5, and as I said, I had no issues with it. YMMV.

[Rick Kirchner]

for some reason I thought dual plates were not allowed?

[stonebridge20]

Like Dave W said, you should have no problem with a single 5.5 as long as you dont abuse it. Throw the clutch assembly in with the other stuff you're sending up and I'll Cryo it for you. I do a bunch of Tilton assembly's for a big vintage prep shop that will not install clutch components that weren't Cryo treated first.
I've got a 1" 23 spline 5.5 disc that's cryoed already for sale at replacement cost if you want it by the way.