clutch size questions

[6667fan]

Hello, I have made the decision to go with a lighter flywheel for my Fairlane. Changing from a Mcleod 29 lb. steel piece to a Mcleod 18 lb. aluminum one that has three bolt patterns, 11", 11.5" and 12".  I ran a Mcleod 12" long style with a ceramic/ceramic disc last year and though I only had a few passes with it it seems like the hit was pretty hard for leaving at 3K. This prompted me to try the aluminum wheel but as this is a street car I'm not going all in on a slipper clutch. My question is will going with a smaller, (and assuming lighter), clutch substantially soften the hit? The disc material will still have to be ceramic or something aggressive unless there are other options for a long style, single disc clutch that will support over 600 ft lbs. The old steel wheel and clutch together weigh 45 lbs.

Thanks,
JB

[blykins]

It is lighter which cuts down rotational momentum.  I usually try to run an 11” clutch for weight purposes unless I have no other choice.

Your best bet will be a RAM Powergrip HD or a McLeod 600 series disc with their pressure plate.

[TomP]

I see no need for a 12" clutch unless you haul a huge trailer or maybe have 44" mud tires. 11" is plenty and has less rotating mass. It makes shifts easier.

[cjshaker]

Any clutch that will hold the torque of a big block is going to hit the tires pretty hard. In my experience, a street clutch that slips on launch won't last long anyway. It will glaze the surface of the disc and probably the flywheel, and then it's junk. In my opinion, you're only real option while at the track, without going to an adjustable, is to learn to slip it yourself.

[TomP]

I used a regular disc and pressure plate in my Fairlane for the first few years, just for drag racing and launching anywhere between 5000 and 6500. It was actually the original clutch from a 429 Torino.  I'd just lift my foot up off the pedal and never slip it off the side (except that time with wet shoes and my ankle took the brunt of that) and it would last OK. That was with a lot of low gear, 3.25 Doug Nash and 4.57 rear end with 28" tall slicks. I'm not sure I gained that much with the adjustable SoftLok clutch since i'd leave a lot of base pressure cranked in and no counterweight. At first I burnt the thing out, warped the disc and pressure rings, by not having enough base and being in eliminations where I didn't want to lift.

[cjshaker]

I used a regular disc and pressure plate in my Fairlane for the first few years, just for drag racing and launching anywhere between 5000 and 6500. It was actually the original clutch from a 429 Torino.  I'd just lift my foot up off the pedal and never slip it off the side (except that time with wet shoes and my ankle took the brunt of that) and it would last OK. That was with a lot of low gear, 3.25 Doug Nash and 4.57 rear end with 28" tall slicks.

That's what finally worked on my car, 4.30 rear gears and a 3.19 first in the Jerico. The stock toploader ratio would hit the tires too hard with the Ram street clutch, even with the 4.30 gears, and trying to slip it was very inconsistent. The 3.19 first changed all that and made the car take off much quicker without hitting the tires so hard that they lit up. Now I can just let out the clutch quick and easy, like Tom described.

I should have been clearer on my comment earlier; slipping the clutch yourself is fine, but once a street clutch slips on its own, it's pretty much toast, and in short order it'll be letting the engine rev freely. There's a reason that nearly all clutches designed to slip on hard launches use sintered iron or ceramic. Organics will glaze too easily. Lots of gearing can greatly help with a street clutch though.

[BattlestarGalactic]

Something ALWAYS has to give.  Clutch or tires, your choice.  It is the way of life with a stick car.

A rag disc will take lot of pedal pressure to hold the power.  A metallic will grab with a lighter pedal feel, but will still be a light switch.  A lighter flywheel will just make the motor bog if the clutch does not slip(or tires spin).  It's real hard to play both sides of the street with a stick car.

I could drive my wagon to work every day with the clutch that is in it and never really hurt it.  BUT...you can't play on the street like you can with a stiff clutch.  If you try to bark the tires between gears...ain't happening.  You'll just drive through the clutch at any RPM under your shift point.  You could take the time to "turn it up" while street driving, then turn it back down when you are at the track.   Just an allen wrench and a 15/16" for the crank bolt with a jack to get under the car.

[6667fan]

I would like y'all to take a look at the drag racing forum and "Had my Fairlane at track day" please. The run shown was a 3K dump with 15.5 psi in the new slicks. The clutch was the 12" Mcleod with the ceramic/ceramic disc. I could not keep making passes due to worry about a thrust bearing going or maybe I would have learned something. My one other pass was a 2500 rpm dump but the tires did not get heated, ( could not get line lock to hold). No spin on that pass. Looking for opinions on what to do clutch wise.

Thanks,
JB

[John67427]

Just something to look at if not wanting to go adjustable pressure plate. Don’t know anyone that has one.       CLUTCHTAMER.COM

Interesting concept

[BattlestarGalactic]

As hokey as the Clutchtamer is, I can see its use and would get you that "slip" you need. 

The tamer is used by the coyote class cars that MUST run a stock clutch and 5spd.  It keeps the parts off the track and gives them the adjustability they need to make the car work.

Your ET is like 11.0 with that 122 mph.  But unless you do a lot of changes to make it more tunable you won't get there.

That ceramic clutch takes a LOT of heat to get it grabby.  It also takes more pressure(or surface area), thus the 12" diameter.  So if it's cold it would likely slip more for you.  Once hot, it would get to be ON/OFF.  For comparison my metallic disc is only 10 1/2" diameter.

If you did downgrade to something a bit less aggressive, use a counter weighted pressure plate you could then have less clutch at launch and have enough pressure at shift RPM to hold it.  Basically what my car has, but maybe not the extreme.  I don't know the weight requirements or surface area needed to make each type of disc work.  You basically need enough clamp load at your max RPM to hold the power.  Anything above that is wasted.  I spent a couple seasons playing with mine til I got it in the ballpark.  It won't be an overnight deal for sure.

[6667fan]

I was on the horn with McLeod earlier today. They in theory have an 11” long style cover plate that has a  counter weighted arm. I say in theory because a year ago when I was  looking for one they did not have any and STILL do not have any. That was what pushed me to the 12” I ran last year.  The part number is in the big supply houses catalogs but you can’t get one and Billy at McLeod can’t say when they will be available. The 11” ceramic 600 series disc is available and so is an 11” diaphragm but the clutch pedal may not leave the floor after 6500 rpm.
I know Brent likes the Ram stuff so might start looking there.

John, thanks for the info on The Tamer.

As part of this continuing expensive grand experiment David Kee just received my TL so it can get rebuilt with some face plated gears.

Thanks much for the perspective Larry. 

JB

[BattlestarGalactic]

Don't understand why they say they don't have CW levers?   They put them in EVERY race clutch.  Not sure if they work in a 12" plate though.  I've bought the levers straight from RAM to put in clutches at home(I've had gift cert to use up).  I've built a few "back up" clutches for the wagon, but end up using them in something else.

Yes, stay away from diaphragm.

[blykins]

Pretty much every disc that’s meant to hold over 450 hp will have some kind of metallic material, whether it’s sintered bronze, Kevlar, or sintered iron.  As long as it’s not an unsprung hub, there should not be any on/off actuation.  Spec clutches are notorious for being on/off but they use a lot of unsprung discs combined with sintered materials.

I’ve got a local customer that runs 10.90’s with a RAM Powergrip HD, sintered iron on both sides, and then drives it during the week.  It has a very easy pedal pressure and slips like an organic disc clutch.

A lot of your Long style plates are counterweighted, and they are listed in RAM’s catalog with a CW on the end of the number.

I wouldn’t recommend an adjustable pressure plate for street drivers unless you’re really good at nailing the spring loads and weights needed and you have a couple big holes in the bellhousing so you can make adjustments.  I set up slipper/adjustable clutches for guys but with all the other options available out there, I wouldn’t recommend it for the average guy. 

[BattlestarGalactic]

I ran a 908? disc(spring hub, sintered iron) in my black car.  It was a left over from the wagon years back.   It was brutal on the street.  It was smooth for the first couple minutes, then it chattered like a bitch.  Either had to bog it or ride it hard and kinda squeak the tires to get it to take off smooth.  After about 15 yrs it was finally done and I put a dual friction disc in it.  Much better.

I know adjustable clutches are not for the faint of heart and even more seasoned racers will screw them up by not paying attention to what the car is doing(most don't have data loggers--like me).  You have to be part of the car and notice what is happening and not just beat it to pieces and then wonder "what happened?".

[blykins]

That's not the norm for those discs, they are pretty smooth.   Been selling the RAM HD kits for 12 years and I have yet to hear one guy complain about any chatter, unless there was a pressure plate spring broken, etc.   Now that I think about it, I've never heard anyone complain about chatter about any of the sintered discs.  The Kevlar can be chattery if it gets hot, but the sintered bronze/aluminum/iron discs seem to be real smooth.