I've got enough passes under my belt at this point that I really feel like a pansy asking questions like this. I'm going to ask anyway, however. I'm looking for some advice on how to leave the line in my T/A. Let me give you just a touch of history so you understand my position.
My car was, for a long time, a 400RWHP cam-only car. T-56, obviously, with a Dana60 and 4.10 gears. With that setup and some 12" slicks, I would usually 60' in the 1.7s. Traction was never an issue. It always seemed like power was lacking to get the 60' to improve.
Initially, this setup was using a Textralia single disk clutch. I left by revving her up to 6k or so and dropping the clutch. Rather than holding the RPMs up, I would stab the gas on the second yellow and just dump the clutch when it got where I wanted it. I was pretty good at timing it.
Later, I switched to a McLeod RXT twin disk, and let me tell you that this is one badass clutch. I started out bogging it a great deal while letting the clutch out very quickly, but not just dropping it. Finally, I got frustrated enough and mustered enough nerve to drop the hammer on it from 6.5k+. I revved it up to no less than 6500 and dropped the clutch and the result was worse than embarassing. The car straight stalled. I was sure I broke something because I heard these banging sounds that I was sure were pistons and rods falling into the oil pan. Turns out, it was just some afterburn in the exhaust. I started the car up and made my pass of shame.
Fast forward a year (and a lot of headaches). The car is now Procharged and puts out more like 625RWHP. I've only had it out to the track once in this state, and I cut a 1.58 60' slipping the clutch a BUNCH and just being real gentle with it. Needless to say, I'm still pretty gun shy with dropping the hammer.
Today I was looking around in the multimedia forum at 6-speed passes in some fairly fast cars. Most of them seemed to drop the clutch. They would hold the RPMs up around 6k and (apparently) stab the gas and drop the clutch. Rather than what I experienced, they seem to get maybe a touch of tire slippage, a great deal of weight transfer, a loss of maybe 3k RPMs, and ultimately a damn nice leave.
Does anyone have any advice for me on this? Should I not drop the clutch the way I did in the past? Is my clutch and tire combo just too much for the power the motor put out (when it was 400RWHP)? Should I try again now that I have more power? Is there something I'm missing?
Advice and/or words of encouragement accepted. Thanks in advance.
EDIT: Here is a video of the pass with the 1.57 60'. My friend's slow 'stang is drowning my car out, so you can't hear much, but you can see how gently the weight transfers...
I see most people who run mid 1.5's do a fastish dump, don't drop it as fast as you can, but try to let it out quickly so the rpm's don't fall down, but don't dump it to where it shocks the shit out of everything.
two of my buddies in there 6 speed cars just cut 1.51(ws6-srt)d1sc and 1.53 turbo camaro(550ish hp) I think they did a fast let out at high rpm 6,000ish.
i have a cam only car i leave at 7k. as soon as you get your second stage bulb lit bring your revs up. now bring your clutch close to the point of engagement when you see yellow turn it loose!. i would think with your amount of power you would not have to rev that high though. my car cuts 1.51 60ft's on a 26X10 mt et drags
That launch doesn't seem too bad, now it's a matter of experimenting and tweaking. Obviously you found out first hand how different parts are going to react to the same sequence of events with the clutch change. Now the challenge is figuring out the process that'll work best with these parts. Next time out try to let the clutch out faster and see how it likes it. 6 speed cars require a lot of tweaking along with trial and error to get them running right but the 2 keys are keeping the engine in the power band and making sure the suspension is working properly. To keep the engine in the power band you either want to have just a touch of tire spin or you want to slip the clutch. Dead hooking after a clutch dump usually results in a bog which will hurt 60 ft times. If your clutch will tolerate some slippage then it may be easier to be consistent and it'll be less abusive on everything behind it. Many clutches won't tolerate that so guys end up letting them out fast and trying to reach that point of spinning just a touch to keep the rpms up and powering their way to a good 60 ft. You have to find out what works. Cars that have real good power/weight ratios and a good suspension setup can handle a clutch dump without tire spin and just power their way through the bog to a good 60 ft. but I don't see that in street cars too often.
I run a Tex oz700 z grip, 380-390 rwhp, 5.5k and dump and it did VERY good. So good that the car picks up the wheels but the body slams on the rear and the tires un load. I picked up the needed parts to fix the weight xfer and keep the front wheels level and when I go back out, thats going to be a big difference.
Drop the hammer and see where she leaves you.
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Thanks for all the responses, guys... especially Kaltech.
I think that with the traction I have in this car, I'm inclined to just work my way up to dropping the hammer. I think the traction and clutch in this setup are enough to either break the drivetrain or stall the car on a dump. I think slippage is going to be necessary, but I'll work my way up leaving harder each time until it's more apparent what will happen on a dump.
I wouldn't try slipping the clutch at a high rpm. After these cars start making over 400-450rwhp, it's really hard to slip the clutch repeatedly without burning the disk/(s) up. If you feel you have to slip the clutch at a higher rpm (over 4.5k), let the clutch cool down before the next pass. Once that clutch disk/(s) glazes,,, she's done and your night of racing will be cut short.
My advice, put a good tire back there, drop the clutch and see what the suspension wants/needs afterward. It's much easier to deal with spinning the tires and making suspension adjustments then it is to glaze a clutch disk.
Mike
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x2 with installing a 2-step. My car launches alot better and is more consistant now that I have a 2-step. Here are 2 vids of my cam only car launching. The first vid is launching around 6000+rpm "without" a 2-step and cutting a 1.75 60'. The secound vid is launching at 5800rpm "with" a 2-step and cutting a 1.62 60'. The only other advise I have is to get a set of decent adjustable shocks. I'm running Starnge DAs in the front and SAs in the rear and they work great.
I see most people who run mid 1.5's do a fastish dump, don't drop it as fast as you can, but try to let it out quickly so the rpm's don't fall down, but don't dump it to where it shocks the shit out of everything.
two of my buddies in there 6 speed cars just cut 1.51(ws6-srt)d1sc and 1.53 turbo camaro(550ish hp) I think they did a fast let out at high rpm 6,000ish.
You're right, Brad. I tried to get the rpm's where I wanted and released it quickly. No dumping. I use 26X11.50 QTP's, and 3.89 gears. And Guage, I'm not making the power you are now. So, I don't think you have to worry about stalling. What helped me most is what you're doing now (asking for advice). Between watching the tree, trying to keep the rpm's where I want, and usually being a little anxious. I often screw something up. I just ordered a 2 step to help this.
Thanks for the additional responses, guys. It's encouraging to hear people having success with dumping the clutch.
What do you guys think about what happened to me when I stalled the car? I mean, for crying out loud 6500+RPM at WOT on a 400RWHP motor, and the drivetrain stopped it dead in its tracks. The car might've moved a foot, and the engine acted as though it has siezed. That definitely shattered the nerve I once had launching this car.
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It dead hooked, and when you dropped the clutch I bet you lifted off the gas and didn't realize it. I did that the first couple times I left off the transbrake in my car, then I realized what I was doing, and wedged my leg stiff at the launch until I got used to it.
Just air the tires up about 3 or 4 psi more then you think you need them, and get a 2 step. Then you put your foot to the floor on the 2 step, when you let go it goes back to the regular limiter...
This way you can try leaving at 5000, if it bogs, leave at 5200, bogs try 5400, bogs try 5600 etc.etc... and go until it spins, then take 1/2 a lb out of the tires until it starts to show a sign of bogging again, then up the rpm 100 more and continue until it's right.
Start at 5400 with 16 psi in the tires and see what happens, you'll get it right and the car will fly.
Definitely get a 15 inch rim and a bias ply tire on the car, at your power level trying to do it on anything else with the stick in the car, isn't gonna work too well. If you had an auto, it would be a differtn story you could leave a 17 inch rim on it and get it to leave in the 1.5's, but the stick, really makes the 15 inch tire sidewall a nessassary item to have.
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Quote:
Originally Posted by J-Rod
First off Hp/L is ricer math, and is pretty much useless
I agree with JL ws-6. If you dead hooked your foot probably lifted without you knowing.
I also agree with AChotrod. If you get a 2-step you'll be able to launch at WOT with will keep the rpms up and you'll be less likely to hook and bog. Just do what I did set it at 5500 and work your way up. I ran my PB launching on the 2-step at 5800. Unfortunately I had to leave that day to attend my niece's and nephew's 1st b-day party so I did get a chance to bump up the 2-step. I'm going to the track this weekend and I'm starting the 2-step at 6000 and working my way up.
Btw, I'm running Lingenfelter's LNC-002 2-step which includes a timing retard function for boost and N2O applications.
Leavin' in a 6-speed 
I just ordered a 2 step to help this.
