Pressure plate weight

[Little Mouse]

How does a diaphragm pressure plate compare in weight to a long style pressure plate say 10.5 size, the diaphragm lighter ? I did use a borg and beck pressure plate one time back in 1970s but never considered any weight differences.

[289nate]

Depends on the long style pressure plate you’re going to use. I have 10” single disc from Rob Youngblood of Advanced Clutches that is pretty light due to the use of aluminum.

[Little Mouse]

Looked up his web site and the 10 inch clutch what are you using it in.

[289nate]

I was using it in my 1965 Mustang fastback that is just a street strip toy. Transmission is a face plated GeForce straight cut gear T5 I built. Engine was a low buck 289 that made 430 hp at 7000 RPM. 4.56 rear gear and 26 inch tall 8 1/2 wide slick. Never really got the clutch dial Dan like I should have utilizing the ultimate to tack overlaying drive shaft rpm with engine RPM. New engine will be a little more robust. 306 with just under 13 to 1 compression more RPM and e85. Clutch and drive train will remain the same.

[289nate]

https://www.google.com/search?q=65+fast ... mZcvw,st:0

Best pass was 11.12 at 122 mph with 60 foot in the 1.5’s. There was more in it but I drop some thing down the carburetor while working on it and didn’t realize it until I started up the engine. Then it let me know loud and clear. LOL

[Little Mouse]

Well that sucks I guess the positive is you get to build a stronger engine. So how does it compare to spending to other single disk clutches looks like more money but will I need to get away with robing a bank to get one ?

[289nate]

Depends on your application. Tim Hyatt, Rob Youngblood, and more recently brought to my attention Black Magic clutches are worth a call to see if it works for you.

[Little Mouse]

Leaning toward a 337 sbc build buying a triumph spitfire moving front suspension forward somewhere 4 to 6 inches and using a narrowed 8.8 ford rear. Now an original spitfire weighs 1750 lbs want to do 1 5/8 roll cage, I'm figuring car would weigh more like 2100/2200 when done
But it would really just be almost all street car. I like light weight, anything I take weight off every motorcycle I have ever owened consider weight as death. I guess I understand the bracket race thing but if I were going to drag race a chevy with a sbc I'd use a monza or if a ford because there cheap in cost a maverick.

[weedburner]

Hi Little Mouse,

I have a street/strip '85 Mazda RX-7 w/ 96" wheelbase that I installed an sbc/4spd into. Instead of extending the front, i moved the engine back 10" to get 2325lbs with 45%F/55%R distribution. Also made a street friendly torque arm style rear suspension, much safer than non-articulating ladder bar or 4-link setups. Hooks in a car wash as they say. If you decide to go this route, early RX-7s are good floor pan donors as trans tunnels are HUGE. That's because a rotary engine's "crank" is up in the middle of the engine instead of down low like a sbc, so their original transmissions are located much higher. Here's a link to my car if you are interested... https://grannys.tripod.com/20102.html

With regards to your question about pressure plate weight differences, here's something to think about for the street-
Actual Racepak data collected from my personal car above, with some rough calculations applied. Sbc power, but exact same car/trans/flywheel/clutch/gearing/tires. Exact same heads/intake/carb/cam/compression. Only difference between these two engines was the rotating assy...

Scat cast crank (49lbs), steel rods, 1863g bobweight, WOT no-load rev rate of 8500rev/sec.
In 3rd gear @ 535rev/sec accel rate, 31.47ftlbs absorbed by the rotating assy, 468.53ftlbs twisting the transmission's input shaft.
In 1st gear @ 1975rev/sec accel rate, 116.18ftllbs absorbed by the rotating assy, 383.82ftlbs twisting the transmission's input shaft.

Scat F43 lightweight crank (42.1lbs), aluminum rods, 1492g bobweight, WOT no-load rev rate of 11,515rev/sec.
In 3rd gear @ 541rev/sec accel rate, 23.49ftlbs absorbed by the rotating assy, 476.51ftlbs twisting the transmission's input shaft.
In 1st gear @ 2217rev/sec accel rate, 96.27ftllbs absorbed by the rotating assy, 403.73ftlbs twisting the transmission's input shaft.

Comparing the two...
...both engines put out the same torque when operating steady state @ 5000rpm.
...WOT 4500-5500 at 3rd gear acceleration rate, the lightweight rotating assy hits the transmission's input shaft with about 7.98ftlbs more torque.
...WOT 4500-5500 at 1st gear acceleration rate, the lightweight rotating assy hits the transmission's input shaft with about 19.91ftlbs more torque.

The difference in bobweight was about 3.27lbs, crankshaft weight difference about 6.9lbs. Flywheel/clutch weight is typically centered farther from the axis of rotation than the crankshaft, making it an even more effective place to lose weight.

Does less weight in your rotating assy actually reduce E.T.? Doesn't make much difference for me, but your results will depend a lot on how you launch the car. If you are launching from less than finish line rpm, you will likely be quicker w/ lighter rotating assy as you will be spending more energy with the engine gaining rpm vs losing it. Same if you are using a lot of wheelspeed or knocking the tires loose after the shifts.

Here's a link to some in-depth info about my views on clutch tuning, very street friendly method that won't leave anything on the table when you take it to the track... https://grannys.tripod.com/clutchtuning.html

Grant

[Little Mouse]

When I was young was into corvettes owned 4 of them liked my 66 vert the best a pure sports car no power anything just a radio and heater as luxury and my plan shortly in 1 1/2 years from now to move to San Diego from dfw tx area have been in since 1978. I know I'm in minority on this but have always liked the looks of the 70 up spitfire with the hardtop they used on those cars. It's very short wheelbase 83 inch it would still be short if I extend the front 6 inches. What I want to do is buy a fiberglass front tilt front end for it then move the front wheel well forward say maybe 4 inches then ad a couple inches on back of the front tilt. Don't want to get a real goofy looking front extended look just stay mostly with a close to stock overall length. In a perfect world would like to have another 66 vette like I once had but the price tag on those to far out there for me unless almost junk to fix up. I'm 5 11" so I can sort of fit in the spitfire car not for tall folks. Will always be more of a sports car person and why do you need all this power everything and A/C in your toy that's not going to be a daily driver anyway. To me vettes we're ruined the day they went the luxury everything rout. In mid 70s when I had the 66 there was still worry around of diaphragm clutches over centering but it never did happen to me so I put in a 3200 lb borg and beck pressure plate and lakewood scatter shield still using factory nodular iron flywheels of the period. My 66 vette weighed 3150 on a public truck scale when I had the sbc in it.

[Little Mouse]

Spitfire uses a master and slave cylinder to work the clutch. Maybe I would be better off using a McLeod 3200 static pressure 11 inch diaphragm pressure plate they make and a sprung hub disc with a sort of medium aggressive material on the disc being as its going to be street driven. I have a new steel flywheel that weighs 36lb drilled for either 11 inch or 12 inch diaphragm clutch I'm never going to use it.

[weedburner]

Sounds like a lot of pressure plate load, how much torque do you plan to make?

Here's a link to Ram's pressure plate page, it lists weights for the different types/sizes... https://ramclutches.com/pressure-plates/

Grant

[Little Mouse]

The 3200lb borg and beck with its sort of short levers was stiff no doubt but that kind of stuff does not really bother me same pressure on a diaphragm most likely not as stiff to release as a borg and beck. I would not go with a total organic plate maybe some combination, have looked at ram pressure plates and disc's and I'm not really stuck on a particular brand just noticed McLeod made that higher pressure plate diaphragm. Only owned one car with a hydraulic clutch just a v6 dodge raider always worked flawlessly and very easy pedal effort. Not seeing much down side to extra pressure on whatever plate I end up with.

[ClassAct]

The 3200lb borg and beck with its sort of short levers was stiff no doubt but that kind of stuff does not really bother me same pressure on a diaphragm most likely not as stiff to release as a borg and beck. I would not go with a total organic plate maybe some combination, have looked at ram pressure plates and disc's and I'm not really stuck on a particular brand just noticed McLeod made that higher pressure plate diaphragm. Only owned one car with a hydraulic clutch just a v6 dodge raider always worked flawlessly and very easy pedal effort. Not seeing much down side to extra pressure on whatever plate I end up with.

You are thinking like it’s 1972. Plate pressure is the wrong way to buy a clutch. You need to look into a soft lock clutch. They work as good on the street as they do on the track. There are only down sides to extra plate pressure. Like broken parts, piss poor shifting, clutch cover flexing and on and on. With a correctly set up soft lock clutch you can run 800-1000 pounds of plate load and leave it.

Of course you can tune it up too. The days of big pressure plates were obsolete in 1975.

[Little Mouse]

Problems come more with what kind of plate is used on ruining parts, solid disks no springs or a real aggressive material used on the plate or both used at same time. I would think the pressure plate is made to handle any extra pressure not flexing if not the manufacture not doing its job
Most put a lot of praise on McLeod but I have never used one.