[weedburner]

I think the typical static+CW "slipper clutch" tune leaves a lot on the table.

The basic clutch tuning challenge for most in drag racing applications is that the ideal amount of clutch clamp pressure during launch is less than what's ideal after the shifts. The traditional adjustable static+CW clutch attempts to solve that problem consistently by using centrifugal weights in a way that makes clutch clamp pressure increase with engine rpm. Lowering launch rpm well below the shift rpm has the effect of relaxing the amount of centrifugal clamp applied, which can in-turn prevent the clutch from pulling the engine down below its torque peak during launch. Then by the time the engine reaches the shift point, clamp pressure has increased to the point where the clutch slips much less after the shifts. More slip during launch, less slip after the shifts. Problem solved?

The adjustable static+CW clutch solution sounds great until you consider this- "driving into" an adjustable clutch at an averaged 6200rpm will produce 52 power pulses during that critical first second after dumping the clutch. But spinning at an averaged 8000rpm the engine will produce 67 power pulses over that same time period. That's a gain of 28% more power pulses during that critical first second after dumping the clutch due to higher launch rpm. Even if the engine makes more torque at an averaged 6200 vs 8000, it won't make 28% more torque at the lower rpm to make up the difference. Higher average rpm during launch definitely has the advantage as far as power production goes. Problem with the traditional "adjustable clutch" solution is that when you raise launch rpm you also increase clutch clamp pressure, which limits how far you can go without upsetting the chassis. I suspect that's a basic reason why James chooses to set his SS/AH car off at 6200 instead of 9500.

There's also a difference in the amount of inertia energy stored within the engine's rotating assy. More energy stored prior to the start of the clock means more energy is available to move the car after the clock starts running.

The key to exploiting launch rpm is finding a way to harness more launch energy without upsetting the chassis/tires with a harder hitting clutch. An alternative to the traditional static+CW method of clutch tuning is to vary clutch clamp pressure in a way that is not dependent on rpm, but rather by controlling clutch clamp pressure externally during launch via throw-out bearing position. This makes it possible to have two separate stages of clutch engagement that are independent of engine rpm- a 1st stage level of reduced clamp pressure that is optimized to take advantage of higher rpm launches, which then transitions to a 2nd stage level of full clamp pressure that's been optimized for harnessing energy release after the shifts. In the end, less energy gets wasted due to excessive wheelspeed spikes.

The clutch also gets easier to tune when you abandon centrifugal weights and then crank-in just enough spring to hold after the shift into high gear. From there use a 2-stage clutch hit controller to control throw-out bearing position during launch. Completely eliminates the centrifugal vs base balancing act, as it allows you to adjust launch clamp pressure without affecting high gear clamp pressure. Far simpler way to tune a clutch, and you won't need help from an expert to dial it in.
...If it slips too much or not enough during launch (1st stage), you dial that in with the clutch hit controller from the driver's seat.
...If it slips too much or not enough after going into high gear (2nd stage), you know you need to adjust clutch spring pressure.


There's also a consistency advantage in a dead hook launch vs trying to control wheelspeed.