Crower 3 disc ?'s

We are running a Crower 3 disc clutch and vary from 10.5 discs to 10.7 discs. We are still trying to get a handle on how much static to put in it vs. how much centrifugal. We have ran it all over, 4 turns and 48 grams, 4 1/2 turns and 33 grams, both of those spread out on 3 levers. Weve also ran 4 turns and 38 grams spread out over 6 levers. Im trying to wrap my brain around what exactly changes when you adjust each. Ive read that the static is equivalent to stall speed. The more you add, the lower the stall speed or higher? We leave the line between 68-7200 rpm. Weve been running 42 lbs inner and 6 outter. When we ran 4 turns and 38 grams on 6 levers at Indy last year it went .972 60ft but rattled the tires. When weve ran the 4 1/2 and 33 grams on 3 levers it hit the wheelie bar...tire speed came up and unloaded the wheelie bar...driver pedaled it...came back up on wheelie bar and went 1.12 and 1.14 60ft on 2 aborted passes. ANY advice, ideas, black magic or voodoo will help!

 

Not yet Mike. One of the other people Ive been talking to said all he ever ran was 3 - 3 1/2 and roughly 33-35 grams but on 6 fingers. The car owner/driver has talked to a guy that said 5 turns and 37 grams on 3 fingers and itll run 5.60s. I hesitate to believe ANYONE who will say set it up this way and guaranteed itll run this. Too many variables between cars, engines, tracks. We keep flirting with decent setups and getting real close I think. I just want to make sure Im helping to make as educated guess as possible. We also had some 'drama' on the team which has since been relieved of thier duties. And I know this is a learning curve, I just want to be in the ballpark.

I will mention 3 1/2 turns to him tonight. We are running Bowling Green this weekend so we will have some time to play a little bit I think.

 

They are Bonifante discs, Rockwell low 60s and only run them once before resurfacing. Are you an advocate of using 6 fingers vs 3? I know the weight doesnt transfer directly from 3 fingers to 6, 48 grams on 3 reacts different than 48 on 6. But if youve got a decent run from 48 on 3, where would you start on 6?

 

Ok...gotcha Mike. Thanks for your help!

 

Whats your shift RPM that has a huge impact how much CWT you will end up with. I have had the best luck with low base and letting the CWT do the real work.This has been true from turbo sbc's to blown hemi's that i have worked on

 

The Rockwell is only a piece of the puzzle and so much of the clutch tuneup is based upon the discs. This is why you will see guys using the same pack all weekend. They pull it between runs, surface it an stick it back in with fresh floaters. If you are not doing this and are changing your packs between rounds to a different pack, this is going to change your clutch setup. How much? Depends on the differences in the aggressiveness of each pack. One might give you more wheel speed, the other less. The tricky thing is they can both result in tire shake.

What tire are you running? The liner pressure seems low to me. What's your clutch and driveshaft graph look like? Wheel speed early is key and needs to be in a controlled manner. The other thing that no one mentioned is that there is several types of static springs available with different pressure ranges. 4 turns on one set may be 3 on another. For this reason, when talking base it is a good idea to talk LBS of pressure not turns. Do you have big or small fingers? What does Crower say your starting point should be? If you talk to Roger out there he can provide you with a chart that your springs should be. If they are old they loose pressure, same as valve springs and it is a good idea to test them periodically on the spring tester to see where you are at.

What the engine is doing also has a reaction on what the clutch is doing. If you are blowing a jet open or closed early or if you are adding or pulling timing it will directly affect how the clutch responds. As you can see there are many variables that can effect the clutch. Try to eliminate as many as possible. Don't add timing, blow a jet open and move counter and base around all at the same time. If you think you need to change the tune up on the engine, do your timing or jet thing and then make changes to the clutch on the next run.

 

Does the stall speed go up or down as you add static?

 

I thought the more static you run gave you more plate load when you let the clutch out, and the more counter weight you added put even more load on the clutch pack ?

 

Plate Load with Static Weight

Correct, just like Mike said. More static equals loading the plate sooner equals engaging the clutch sooner equals lower engine rpm (stall speed) as some call it. I have a 3 disk pedal clutch and that is how it works for my set-up, too.

 

100 lbs of static is 100 lbs from idle to 10,000 rpm 10 grams of counter can be 150 lbs @ 5000 rpm to 800 lbs @10,000

 

Thanks for your help andexplanations Will. I got back to read this AFTER you stopped by Saturday. Its starting to make a lot more sense now. Hehe.

 

Something else to think about that can and will give you fits is swapping back and forth from 10.5" to true 10.7". Doesn't seem like much of a change, and it has been a couple years since I've worked with discs daily so bear with my numbers.. 10.5" discs used to have around a 6.800" inner diameter, 10.7" would have a 7.0" standard, others would cut it back even more.. Why does that matter? Clutch capacity is directly related to the mean radius of the friction surface. So, assuming your surfaces are dead flat, the distance from the center of the input shaft to the center of the friction material.

I have seen cars run combos of even 10.7" with different IDs, 2 standard and 1 cut-back. Tune up was right in the wheelhouse with that combo. Anytime you changed that combination to either 3 standard or 2 cutback and 1 standard, it would do something stupid. Changing 1 disc inner diameter in the pack made the difference between that tune up making it or damn near shaking the wheelie bar off. The only reason it was like that is we learned to tune the clutch based on that package and didn't want to spend the time and laps to figure out a more consistent package. I have also seen cars using 10.5" discs in a 10.7 clutch go from .970 60 foots and easy to shake to .930's and become an absolute rocket to the 330 just by changing from 10.5" to 10.7" discs. Doesn't seem like it would do much, but it can make a world of difference.

When clutches work, it feels like voodoo magic, but the only magic to the clutch is CONSISTENT PREP. Work the same stuff the same way every time. Do yourself a favor and get your stuff dead flat and the same size and you will begin to notice how your adjustments are working. Working with inconsistently sized and prepped clutch parts is just like being a one legged man in an ass kicking contest.