y8s

iTrader: (8)

the difference between organic sprung and unsprung is trivial compared to the difference between organic and (semi)metallic puck clutch.

bbundy

Organic won't hold my torque well unless it is a twin.

With an ACT Going from a 1.8l HDSS organic to a 1.6l XTG6 6 puck I noticed surprisingly little difference in drivability. It launches smooth and consistent doesn’t judder at all.

Bob

y8s

iTrader: (8)

oh right, not organic.

I ran the tilton cerametallic disks when I first installed the twins. they were solid hub. I can't really say if the sprung hub would make a difference but these disks did not slip so I can't see how a sprung hub would make a difference.

that said, it's probably fine. those springs are pretty small compared to the forces in a clutch drop. I'd wager they bottom out pretty fast anyway.

bbundy

That is what I think. I don't think there is any way they could be stiff enough especially on a 1.6l size disk. The slop they have before they bottom out just serves to make it work sort of like a slide hammer and the impacts would be harsher to the drive line components during shifts and launches.

I just ordered a 4 puck solid disk.

Bob

y8s

iTrader: (8)

seriously never noticed a difference in "gentleness" going from stock sprung hub clutch to unsprung twin organic to single sprung FM level 1 clutch. it all feels the same for engagement.

PatrickB

iTrader: (1)

I have a happymean w/ the 13lb flywheel, feels pretty much the same as stock.

bbundy

Fine if you like stock. I like the feel of a stupid light MOI though. Every pound off the clutch and flywheel makes it feel better to me, just need an engagement very slightly smoother than an on off switch without a ridiculous amount of shudder. I am sure Id like the 949 twin.

Bob

bbundy

Got the new disk

Un-sprung 4 puck 1.6l = 1.75# for the disk
Sprung 6 puck 1.6l = 3 lbs for the disk

When the sprung 6 puck came out it was as I was thinking. The pucks were fine but the sprung center was on the verge of exploding. A couple of the rivets holding the center sprung mechanism together were pulled out from the slapping hard against the end of the spring travel. 300+ ft-lbs is too much for that small sprung center.

Bob

y8s

iTrader: (8)

Bob, any chance you could measure or calculate the spring rate?

http://www.engineersedge.com/spring_comp_calc_k.htm

calculate individual spring force:
F = T/(r*n)
(where r is the radius to the spring centerline, T is torque, n is num springs)

calculate spring displacement
x = F/k
(x = displacement at force, k = spring rate, calculated above)

and then (spring installed length - spring block height (fully compressed))

to see if the spring is partially compressed, fully compressed, or just plain smashed immediately.

ie I'm curious if they do anything.

miata2fast

iTrader: (2)

Instead of springs, my clutch disc has rubber bushings. When I flatfoot shift, there seems to be more of a thud than with the old spring hub disc. I speculate that the bushed hub would be lighter than a sprung hub.

Is that common in the clutch world to have a rubber bushed hub? Perhaps a bridge between a solid hub and a sprung hub? I can not say that I have seen it before in other discs.

bbundy

It is sort of interesting I swear I have had 1.8l ACT HDSS clutches which should be all the same parts and some have had steel springs and some have had rubber. The rubber ones seem to be incredibly more durable.

Oh and a 1.8l SS disk is slightly lighter than the 1.6l sprung puck. The pucks themselves are heavy. The 1.6l pressure plate is lighter though. I just realized I have both 1.6 and 1.8 pressure plates out now, I will weigh pressure plates tonight for comparison.

Bob

ZX-Tex

iTrader: (15)

That is an interesting observation. My guess is that the difference in durability is due to the different end of travel behavior of the two. The spring clutch eventually hits the spring lock and thus there is a sudden, big spike in stiffness (k). The rubber one essentially has its stiffness climbing continuously. It is like a bottomed out suspension hitting spring-lock instead of a rubber bump stop.

bbundy

Ok the pressure plate weight between 1.6 and .1.8l wasn’t as big as I thought. The Iron friction part is smaller but the stamped cover part is a bit more elaborate on the 1.6l making back some of the weight.

1.6l ACT Extreme PP 8.25 lbs.
1.8l ACT HD pressure plate 9.25 lbs.

What is going in my car,

1.6l Fidanza Flywheel----7.5 lbs.
1.6l 4 puck unsprung disk ----1.75 lbs.
1.6l ACT Extreme pressure plate ----8.25 lbs.

Total rotating assembly 17.5 lbs. For me it is streetable and it holds 300+ ft-lbs of torque reliably at the lowest weight available before stepping up to the 949 twin.

Bob

Gotpsi?

iTrader: (5)

949 lists the twin ceramic at 15.7 I believe,

bbundy

I suspect the 949 has a much lower MOI though, not as much of the weight that is there is out on the perimeter.

Bob

Gotpsi?

iTrader: (5)

Yes that is true.

miata2fast

iTrader: (2)

Since we are talking cluthes, I know that there is also a 5.5" diameter clutch available. I talked to a Gentleman at Prather racing about it. We did not go into specifics, but I believe it is used in some of the unlimited naturally aspirated classes like E prod and such. Still uses the stock fork.

I have my doubts that a 5.5" would cut it in my application, but would love to drive a car with one just to see what it was like. I can only imagine blipping the throttle of a wildly modified BP with that clutch.

bbundy

I've driven a GT4 Bugey Sprite with a 5.5 Tilton. It was drivable for me if you always were launching hard. Kind of an on off switch. It wouldn’t handle much stop and go without overheating it though. It would probably need frequent disk replacement if you drove it on the street.

FWIW Mazdamotorsports sells 3 versions of flywheels for the 5.5" clutch. Steel with an aluminum ring gear ~4 lbs for the flywheel. A Tilton ceremetalic twin Rally clutch to fit it weighs 6.1 lbs and holds 500 ft-lbs.

I suspect getting the car rolling from a stop would often involve some wheel spinage with that setup.

Bob

miata2fast

iTrader: (2)

That is a lot of torque capacity. Much more than I thought.

I am not to concerned about street drivability. I just want it to be fast.

Many have told me that a light clutch and flyweel is not good for drag racing, but the higher big budget cars have pretty darn light clutch and flywheel combos. In my experience, lighter seemed to be better. In saying that, I would have to think that eventually you get to a point that the weight of the clutch would affect a drag car's 60' time enough to actually lower total elapsed times.

I hate to invest that kind of money only to find out it just does not work. However, if a clutch expert says to go for it, then I might. I wish I could get my hands on one to try without ponying up.

bbundy

It depends on your ability to launch it. I've seen autocrossers use things like this and luckily the stage like is back a bit from the start line so the launch isn’t usually very important. Starting off involves a bump with some wheel spin to get the thing rolling a tad then you can start applying throttle. It is hard to do consistently especially if your starting off a tree. Once rolling the lower MOI has a huge effect on improving acceleration. In road racing how well you start from a dead stop is not really important at all.

Bob