Racing Clutch Match
Racing Clutch Match
(OP)
Im trying to figure out plate load math, torque capacity formulas for a drag racing clutch. Crower pedal type used in the NHRA alcohol dragster/funny car classes. These are 3 disk, lever type with counter weight and static springs. Any clues? I'd like to build a spreadsheet to make tuning decisions.





RE: Racing Clutch Match
RE: Racing Clutch Match
www.crower.com/pdf/181-182.pdf
its the 10.7 Titanium Glide
RE: Racing Clutch Match
The clutch "clamp load" has two basic variables. One is the load imposed by the springs, often called the static load. This does not vary with RPM. The other is the centrifugal load or dynamic clamp load. This increases with RPM and can be changed by adding additional counterweights to the levers.
Calculating the static load is easy and is basically just as you described. If you know the spring rate, thread pitch, and number of turns, you can get the static load.
Getting the dynamic load is more difficult. You need to know EVERYTHING about the levers including, but not limited to:
The weight of the lever,
The center of mass of the lever
The dimensional relationship between the center of mass, the pivot hole, the load apply hole, and the counterweight hole. All of these must be known with the "plate height" at a defined position.
Then using F=ma and the priciples of leverage you can calculate the dynamic load. In the equation, the clamp force (F) is the dynamic clamp force, the mass (m) is the mass of the lever without any counterwieghts. The centripetal acceleration (a) is defined as the angular velocity squared (omega squared) multiplied by the distance of the center of mass as measured from the centerline of the clutch assembly (r).
This same equation is used for the added counterweight. The omega squared is the same, but the (r) will be a new value because the counterweight hole is at a different location from the center of mass.
My Excel programs use the engine dyno data and HP correction factor to calculate the required clamp load and the actual (as best as actual can be calculated) clamp load (static and dynamic) of the clutch for a particular day. The crew chief can then get the right setup right out of the trailer. Minor adjustments for track conditions must be made. It creates a chart that shows when slipping stops, engagement begins, and how much excess clamp load is applied at the higher RPMs.
The basic equation for clamp load on an axial type clutch is:
T = (F) x (mu) x (D+d)/2
where: T = torque
F = clamp load
mu = coeff. of static friction
D = OD of friction surface (clutch disc OD)
d = ID of friction surface
This equation is for one disc. Multiply is by the number of disc you have in your multidisc clutch.
There are other things that must be accounted for such as "effective area". The clutch disc has rivet holes, slots, etc. that reduce the "effective area".
I hope this helps and I didn't confuse you.
BTW, who's Alcohol Dragster/FC are you helping out?
I have an NHRA Competition Eliminator dragster.
Regards,
Greenlight
RE: Racing Clutch Match
I've built many sophisticated financial spreadsheets in my real job but beyond addition/ subtraction of dollars and cents I'm lost. Would you be willing to share some of your work? I'm in the process of getting some lever data from Crower.
Look me up on insidetopalcohol.com under user J Shafer, send me a PM and we can get in touch. Thanks.