I have been reading up on Carroll Smith's "_____ to Win" books, and making progress on bench building a mid-engine rear drive car for E Mod SCCA use. Ran some numbers on the proposed drivetrain, and am struggling to see how it will ever make traction with the not-exactly-earth-shattering torque. I'm fairly confident I'm missing something, but I can't see the forest for the trees.
Have chassis dyno torque curve. Have gear ratios. This gives me a table of torque at the axle (rpm vs gear). Have tire size, so can figure thrust based on torque table. Max thrust in first gear is 3400lbf.
Traction is a factor of coefficient of friction of the tire and weight on the tire. Coefficients are shrouded in dark magic, but race slicks seem to be in the 1.2-1.7 range. If I assume 100% weight transfer to the drive wheels (ridiculous assumption), I have 1750lbf of weight working for me. So - if I wheelstand the car on the best road race slicks I can find, I still can't use all the torque.
How does, say, a Factory Five Cobra running a beefy LS (or other high power, low weight 2wd vehicle) put power down effectively on launch? Traction control? Throttle modulation?
throttle modulation if old and traction if the car has it. 1st gear is trouble for most cars!
In reply to Robbie :
Huh. I wouldn't have called that listening and watching them in person, but I'll buy it. This is not a problem I've ever had; my cars have always been either underpowered/overweight or traction controlled or both.
More realistic would be a 70% weight bias after transfer, with 1.5 friction coefficient due to slightly cool tires between runs. Still get wheelspin through the top half of second gear. 
I may have to actually learn how to drive if this plays out.
Thats the hard part of building a monster. Learning HOW to drive it. Building is easy.
I'm assuming you are using HP tuner for the ECM? Or are you carb on an LS base? If it's HP tuner then you can also play with the throttle pedal settings if you have a DBW setup on a Gen IV ECM.
In Betty which is about the same style setup as you have only a little heavier because she is a road car, (2800 LB wil a mild 400WHP/400WTQ LS3) I have the first approximately the first half of the pedal travel set pretty soft so that the you have to really press the pedal to get full boogie out of her. It helps me not just smoke the tires off the corner.
I can't dump the clutch above 3K otherwise I'm just smoking the tires even with a T2R in there but less likely to do that when I'm launching at about 2500 RPM.
What's the value at say 1200 to 1500 rpm?
Of course it will do a burn out if you dump it at 3k.
Rolling friction is much different than static friction.
In reply to bmw88rider :
I'm not working on the LS platform, the Cobra with LS combo is just a conveniently comparable and relatable example. If anything, it should be harder to drive than my proposed setup. I like the idea of a "two stage trigger" with a soft top half and heavy bottom half of throttle travel.
In reply to wvumtnbkr :
Absolutley, I remember the lecture about friction coefficients now that you mention it. Torque is within the usable range up to about 2200rpm in first. I assume the furtive numbers for coefficients are largely static? If the rolling coefficients are notably higher, as long as I don't dump the clutch at 3k.
wvumtnbkr said:
What's the value at say 1200 to 1500 rpm?
Of course it will do a burn out if you dump it at 3k.
Rolling friction is much different than static friction.
I think you mean sliding friction is very different than static friction- as the goal for tires it to keep it in the static friction range.
