Cause/effect of clutch disc weight

[tsitalon1]

Hey guys,

I have been trying to figure something out and it has brought me to the idea of clutch disc weight.

Knowing that we have puny syncro's in our cars, what is the effect of a heavy clutch disc? would the momentem (kinectic energy) of a heavy clutch disc make it harder for the syncro to macth rpms?

Example:
I would imagine that if the stock oem disc was 1lb and the southbend 6-puck was 3.2lbs then there would be some high rpm shifting issues right?

I ask this of you guys, I want some numbers.. I'll start it off.

Southbend DXD 6-puck sprung hub = 3.2lbs (told by southbend..not verified)
ACT street disk = ??
RPS turbo clutch disc = ??
Stock 1g clutch disc = ??
stock 2g clutch disc = ??
??
??
??
??


Thanks,
James

 

[pneumo]

OK, the ACT street disc also weighs 3.2 pounds on my scale.

You're right about the weight of the disc having an affect on shifting. Unsprung discs are lighter, and puck type clutches save weight around the outer perimeter. An unsprung 3 puck clutch would shift really quick at high rpm.

 

[tsitalon1]

Well, Yes and no. My 6-spuck sprung hub shifts like ass at high rpm but like butter at low rpm. Maybe because the weight of the pads are at the outter edges of the disc.

3.2lbs? Then Southbend must be off on my disc... Whan I take it back out I'll weigh it.

James

 

[pneumo]

The weight of the Southbend disc might be right. I remember weighing the sprung 6 puck disc on my Spec stage 3 clutch and it was roughly the same as the ACT disc I was replacing. I noticed the ACT disc uses a thinner steel backing behind the friction material, where the Spec sprung 6 puck disc uses the same thick material from the hub to the outer edge. I think ACT did this to keep the weight down at the outer perimeter where weight has a larger effect on shifting.

 

[pneumo]

Update:
I just got a sprung 6 puck disc with bronze pads from horsepowerfreaks.com. It has a Southbend Clutch label on the box, and it looks the same as the SPEC Stage 3 clutch disc, too. It weighs 3.2 pounds, exactly the same as the ACT street disc.

It's also the same thickness as the ACT street disc, so I'm going to use the 6 puck disc with a 2100 pressure plate. The pressure plate that comes with the SPEC Stage 3 clutch is lighter than 2100 pounds, it's probably a stock replacement PP.

 

[raped]

I'm bringing this one back from the dead.

I'm looking for the lightest clutch disc available, I want the quickest high RPM shifting on a single disc clutch. Currently I'm looking into purchasing the ACT unsprung 4 puck. Does anyone know the weight of this disc or any other clutch discs that are designed to be lightweight? How about the Exedy stage 2 cerametallic 3 puck?

 

[pneumo]

I'm bringing this one back from the dead.

I'm looking for the lightest clutch disc available, I want the quickest high RPM shifting on a single disc clutch. Currently I'm looking into purchasing the ACT unsprung 4 puck. Does anyone know the weight of this disc or any other clutch discs that are designed to be lightweight? How about the Exedy stage 2 cerametallic 3 puck?

I can add another disc to the data; The Exedy organic disc is 6 ounces lighter than the ACT organic disc, and the Exedy has slightly softer springs in the hub, so it engages very smoothly. I'm currently running the Exedy disc with an ACT2100 pressure plate in my daily driver FWD turbo Laser and I love it! No slippage around the 325hp level, shifts noticeably quicker than the ACT organic disc and engages smoother.

The Exedy 3 puck should be the lightest, but it's rated for low power. If you combine the 3 puck with a 2600 pressure plate it should hold more power, but it won't handle any heat or slipping. Hard drag strip launches will burn it up quickly.

Another tip for quick high rpm shifting is don't use a superhero pressure plate with an aluminum flywheel. The heavy pressure plate will flex the lightweight flywheel and slow the shifting.

 

[bastarddsm]

Its not the weight of the disc, it the Moment of Inertia. It would be difficult to calculate, but easy to measure.

Also our cars don't really have puny synchro's Most domestic 4 speed synchros are the same size.

 

[raped]

Its not the weight of the disc, it the Moment of Inertia. It would be difficult to calculate, but easy to measure.

Also our cars don't really have puny synchro's Most domestic 4 speed synchros are the same size.

Yes, it is moment of inertia which equals mass*radius^2. This means that weight that is further from the center of the disc has exponentially more effect on the synchros ability to change the speed of the input shaft and the clutch disc quickly. A heavy clutch disc will shift noticably slower than a lighter one. If you have ever driven a car with a twin disc this is very obvious.

Since moment of inertia tells us that weight further from the center has a greater impact on the synchros ability to match the speed of the assembly I want to avoid discs with a lot of weight on the perimiter. Discs such as full faced metallic, 6 puck, and other discs that have a lot of heavy friction material on the friction surface. This is why I am leaning toward a 4 puck or even a 3 puck clutch. I am probably going to go unsprung just to save as much weight as possible.

pneumo - Good info. I was looking for a way to purchase an exedy 3 puck disc only (to use with my ACT 2600 pp) but I wasnt able to find a way to purchase it separately. I didnt look very ghard though, maybe it's available. This setup is for my daily driver so an exedy organic isnt out of the question but i don't think it will hold up the the abuse I'll be putting it through.

 

[donniekak]

Its not the weight of the disc, it the Moment of Inertia. It would be difficult to calculate, but easy to measure.

Also our cars don't really have puny synchro's Most domestic 4 speed synchros are the same size.

Yes, but they aren't shifting at 7-9000 rpm's. I do agree though, it's not the physical size that is the main problem, it's the design. A 3-piece design like the w5mg1-w6mg1, 1-2 synchro would work much better.

 

[bastarddsm]

Yes, but they aren't shifting at 7-9000 rpm's. I do agree though, it's not the physical size that is the main problem, it's the design. A 3-piece design like the w5mg1-w6mg1, 1-2 synchro would work much better.

Heheh...I've been for many wild rides in my dads mustang with a fiesty 289 and a slightly modded BW t-10 that didn't mind being flat shifted at 8000 with an 11" clutch.

Hell even his heavy ass Richmond Gear 5 speed flat shifts at 7 with ease.

My double synchro'd second shifts ####ing amazing at 8500 with a XTD 6 puck and standard preloads.

I'm half tempted to "proshift" my 3-4 so it will flat shift at 8500.

 

[doubled07]

I recently put the new ACT Twin Disc setup in my 1g. Very happy with the results. slips very well for a twin setup. I've put over 300 miles on the setup breaking it in. no problems what so ever. Entire clutch assembly with flywheel and flywheel bolts weighed in at 16.36lbs Rev's like a street bike. The only thing that bothers me is the drivetrain noise that I get when gearing down. sounds hellish so I just avoid it now by putting the car in neutral and using the brakes like an old person. I guess from everything that I have read this just a common thing with twin setups. No one can tell me why it just is. Probably doesn't help that all the bushings in my car are urethane bushing.
If you're on the edge between a street disc/puck setup I would recommend this.