Technical Does size really matter......clutch size that is.

Bear with me as high performance stuff isn't my regular thing. '28 Tudor, 327 (maybe 325-350hp) boxed frame, 9.3 (3.90 or 4.10) rear with 7.50 tires. I have a bunch of 10.5" bell housings and I like the idea of a smaller size firewall/floor bump. Do I really need an 11" clutch with this lighter car, even if I might want to try some cheater slicks at the Antique Nats a few times.

My thinking is a 10.5 is going to be fine as it's not a high hp engine, it's a semi light car with smaller tires. I'm getting mixed messages from Mr. Google, some say ok while others say bigger is better every time.

 

I’ve used 10.5” clutches I. Higher hp and heavier cars with no problem. But I would recommend something decent though instead of just a stock auto parts unit. I’ve had good luck with Centerforce street clutches.

 

I'd say it would be just fine. You could go to a heavier clutch setup if needed at a later date still in a 10.5 setup.

I ran the stock 10.5 size with a heavy duty zoom clutch setup behind a nicely built 389 with a m22 Muncie and 3.23 gears. It took more leg effort but never had the clutch slip.

 

Why do I get the feeling that somebody is going to claim this thread is shifty.

 

If you're building a car that really needs a scattershield, then it probably doesn't matter what size clutch you have, as far as floor hump size, eh?

 

10.5 bell is a stock cast aluminum piece so only good for hi performance street use. Centreforce makes a dual friction diaphragm style with counterweights for high rpm engagement assist. Plenty for your combo. You may need to buy their specific flywheel.
Will the sanctioning body allow a bellhousing blanket?

 

It's important to use something that has a good hub construction. I've twisted a couple out with just a stock 292 engine. As mentioned, beware of the parts house brands. Many are imports that may or may not live up to a 327. Most of all it depends on how you are going to use the car.

 

I wouldn't worry about the clutch since you say it has 7.5" rear tires. Even with slicks, I doubt you will have a problem if you are only making a limited number of passes. If you already have the car built, then try it and see what happens. You would still only be replacing the clutch one time.
If however you are assembling for the first time, then by all means go with a better clutch right from the git go. They make clutches that have a different facing on one (or both) sides for higher performance. I recommend Ky Clutch 502 955 9173. They make whatever you want and are a lot less expensive than the "name brand" stuff. They ship everywhere and will answer all your questions. Everybody around here uses their stuff.

 

I would use an organic disc on cast flywheels.... I used kevlar on mine and it wore the flywheel surface bad....Steel flywheels maybe okay....

 

The bell housing has a different contour for the smaller clutch. I won't know 100% if that matters until I start mocking it up. Just getting some ideas ironed out since it's raining here and the garage is full (can't get to the '28 to work on it). I was thinking that there are many options for the 10.5 for higher performance if needed and the idea of draging it was just that, an idea...sounds fun though. The true use will be a driver, almost daily.

 

I totally understand all that. But what I was getting at was that you probably want a scattershield on it, if you plan to go racing at all. And they make them to fit the big clutch, they don't make a smaller size, so you probably want to make room for the big one. Planning ahead.

 

I can't help but smile at the " scattershield mandatory" camp who very seldom beat the safety drum so loudly for automatic transmissions that afford no more protection from an exploding convertor than an aluminum bell does for a manual , & convertors do explode . Well , not very often , you say ? How often does it take ?

 

Huh...NHRA doesn't seem to share your views.

I've never seen or heard of a converter exploding, but my friend's 55 had some interesting holes in the dash from the clutch coming apart. It was quite a bit slower than the ET that required a scattershield.

 

No you do not need an 11" clutch. You could run that one on a 9.5 and live.

Here is an option. If you want to run smaller diameter for whatever reason you can always go to a multi disc clutch. It gives you increased friction area without increasing the diameter.

 

One thing not mentioned is pedal effort. Bigger clutches require more pedal effort, which if you're a 'older fella' like me with maybe questionable knees can definitely be a consideration. And as a class, diaphragm-types require less effort compared to an equivalent B&B or Long which is why they're nearly universal as OEM these days.

 

the multi disc clutches are another option for old farts. Less spring strength required on a multi disc.

 

I have to disagree with you on that @Crazy Steve. A larger diameter may actually require less pedal effort due to thr larger surface area of the clutch disk.
That said a smaller clutch can have a much higher pedal effort depending on the clamping force of the pressure plate.

I went from an 10.5" Long Ford clutch to a 10.5" diaphram and the pedal effort went from eye watering to 3 toes effort.

 

Like he said, diaphragm clutches require a lot less pedal effort...

 

Uhhh, I thought that was what I said....

 

I was looking at those, just in case. The original plan was to run the 10.5, with a good aftermarket clutch and see what happens. I was also thinking of a Z bar to help with the effort and if I need to change the rotation. Again just thinking aloud until I get things mocked up to see where I'm at.

 

Check this out:

 

You don't need an 11" clutch but, I think building some flexibility into the car so changes can be made later should you or even the next guy decide to race it or change up the combination.

 

I run an 11" Zoom diaphragm clutch. With the hydraulic clutch, pedal effort is close to the stock feel.

 

1oldtimer in my opinion to answer your question, size doesn't matter. The type, make and design do. I personally won't run any stick shift car without a scatter shield period. If you are building/designing the car now add the scatter shield functionality into it from the start. It's too hard to change later. I agree with Jim on being able to change clutches with the scatter shield. And as far as auto trans converters exploding, I've never seen or heard of that happen either, I'm not saying it never happened I just have not heard of it. Try to build for as many possibilities as you can. When I built my 36 Willys I always thought about being able to repair it if I broke down on the road, "can I fix this". Also I have used Center Force clutches and find they work very well. Long winded post over, Good Luck.

Pat

 

Here is some info that might be helpful though maybe not directly applicable.

 

Hmm, looks like the scatter shield has a smaller foot print then the stock 11" bellhousing. Quick time makes one for a 10.5 clutch which would be smaller also, but the 10.5 scatter shield isn't SFI certified.

 

How about an old Ansen cast iron 2 piece one? (not mine, just a picture from Google).

 

I use Chevy truck bell housings only. The clutch drops out the bottom and I like the starter on the bell housing rather than on the block.

 

I do like a Zoom clutch. I ran a 10" Zoom (maybe a 10.5) in my old 12 second '55 Ford. Damned good clutch.