The 2-step tells me dragstrip performance is probably important to you, the gears tell me you also want to drive the car on the street a lot. I would suggest adding more clutch. Your current setup is going to bog a lot after launch due to your gearing, then if you slip that clutch long enough to make up for the lack of gear, it's going to be really hard on the organic side of that DF disc. Leaving at a low rpm will help the clutch, but you will be leaving a lot on the table at the dragstrip. I would recommend a disc similar to a Ram 900 series with a damped hub (it's the disc they use in the Powergrip HD), then add a ClutchTamer to control the hit. With that setup you will be able to bump that 2-step to 6k if you want to.
Here's why it's hard to make radials work with a manual trans at the dragstrip...
Radials basically need to dead hook, as they will tolerate very little wheelspeed. To help illustrate how this becomes a problem, lets imagine a car launching with no clutch slip at all- engine rpm with a dead hook on the starting line would equal "0". Lets also say the car has a constant acceleration rate in 1st gear, and the potential to reach it's 1/2 shift point of 7000 rpm at about 2 seconds into the run. If starting line rpm equals "0", and rpm 2.0 seconds in equals 7000 and acceleration rate is constant, at 0.5 seconds engine rpm would be 1750, at 1 second in engine rpm would equal 3500, and at 1.5 seconds 5250 with the tires dead hooked and no clutch slip at all. Obviously dead hooking alone is not the answer, as our engines don't make any power at zero rpm. You NEED some controlled clutch slipping to keep those radials dead hooked without dragging the engine down too far, as there's just no way any combination of spring rate and/or suspension adjustments can possibly absorb enough engine rpm over a long enough time frame to make the radials work.
Here's how controlled clutch slip can help-
To a point the longer a clutch slips, the more time the car/engine has to gain speed/rpm before that clutch locks up, which in turn means engine rpm does not get dragged down as far. Lets apply the above example to a magical engine that has a completely flat torque curve of 500 ftlbs from 1500 to 5500 rpm. If that engine's clutch only slips for 0.5 second, rpm gets dragged down to 1750 after launch and that engine is only making 166.6 hp at the low point of the bog. If the clutch were to slip for a full second, rpm only dips to 3500rpm which effectively doubles it's power production to 333.2 hp thru the low point of the bog. In the real world the difference would be even more dramatic, as it's pretty unlikely the engine would be making 500 ftlbs at 1750.
When it comes time to shift, the problem for radials then becomes the fact that the rotating assembly must almost instantly shed about half of it's stored inertia energy due to the ratio change. If that excess energy is dumped into the chassis/tires all at once, there's a good chance that extra energy will be enough to knock the radials loose, resulting in far less productive instant spin rather than effectively propelling the car forward. Adding a ClutchTamer makes it possible to spread that inevitable energy transfer over a longer time period, reducing it's peak to a level that doesn't knock the radials loose. Also because the car is gaining speed during those periods of controlled clutch slip, the overall amount of energy that must be dumped due to the ratio change is also reduced.
A ClutchTamer makes it practical to choose a clutch with plenty of torque capacity for the application, one that might otherwise grab too aggressively for a radial, then allows "dialing in" longer clutch slip as needed to raise the bog rpm without reducing that clutch's overall holding ability. You might try to accomplish the same thing with your foot, but you will find it impossible to achieve the same degree of precision no matter how well trained the foot.
There may be other ways to make a radial work with a manual trans, but my way works pretty good.
Grant
