98cherrySS

iTrader: (2)

Hi, I'm curious what RPM people are launching off their 2-step with drag radials (at the track)? I'm in a 6 speed/4:10. I have Proxes TQ DR's which seem to grip better on the street than any other drag radial I've used. At least better than Nittos and BFG DR's. Looking for guidance on what RPM and/or technique has worked for others.

Thanks,

Randy

ddnspider

iTrader: (26)

I would leave between 4-4500 but I made alot of torque.

weedburner

Put one of my clutch hit controllers on that clutch and you will be able to dead hook a radial friendly 6500+ launch if you want to, definitely quicker than leaving at 4500 if you are launching NA.

Grant

98cherrySS

iTrader: (2)

What is a clutch hit controller?

98cherrySS

iTrader: (2)

Didn't expect to be able to launch that high. Does it bog and then go?

weedburner

A clutch hit controller is a device that allows you to adjust the rate that a clutch pulls the engine down during launch, helps you find that consistent balance between bogging and spinning. Basically allows you to raise stage rpm high enough to prevent pulling the engine below it's torque peak without either breaking parts or knocking the tires loose. Stick shift racers at the national level are now winning races on radials using my devices.
Here's a link to the info page... clutchtamer.com

Grant

lynx853

iTrader: (8)

So here is the real answer and you may not like it:

It depends. It depends on your setup and track conditions. if you're running on 17 or 18" rims with drag radials, start at 3K, and if you spin, start turning it down, if you hook start turning it up. a little bit of tire spin/slip off the line is ok. but it's all about dialing it in.

If you're running on 15" rims with big tires, you can start brining the RPM higher. For the street I personally do 2800, Track I start around 3K and see how prep/weather conditions are.

98cherrySS

iTrader: (2)

This is pretty wild! I'm not there yet tho. Thanks for sharing!

98cherrySS

iTrader: (2)

Perfect. This is what I'm looking for. What size tire and brand tire are you on? I'm using 315/35/17.

weedburner

Controlling the clutch hit is about controlling the rate that rotating assy inertia hits the drivetrain as the clutch engages, very important if you want to consistently hit radials with a lot of power-

Let's say it takes about 56 ft/lbs of torque applied for about 1 second to accelerate a "typical" rotating assy from 4500 to 5500, also that it takes the same 56 ft/lbs of brake torque to slow that same rotating assy from 5500 to 4500rpm in one second. 56 ft/lbs might not seem like a lot, but when that 1000 rpm change happens over a tighter time frame, the numbers start to get interesting. Acceleration and de-celeration times and the torque required to accomplish them are inversely proportional, cut that 4500-5500 acceleration or 5500-4500 deceleration time in half, torque required doubles to 112ft/lbs.

Quick nitrous cars with automatics don't lose rpm on the launch, and lose very little on the shifts. But with a stick shift car, you need to make room for the energy exiting the rotating assy during those times when the clutch pulls the engine down against WOT. Lets say a clutch pulls this "typical" rotating assy down from 5500 to 4500 in 0.25 seconds after the hit. That thousand rpm drop over two and a half tenths of a second represents an average of an additional 224 ft/lbs of inertia torque applied to the transmission's input shaft. Since a 200 shot represents 191ft/lbs @ 5500 and 233 ft/lbs @ 4500, it quickly becomes obvious that another 200 or so ft/lbs of nitrous should not come on until after the inertia discharge is over. Kinda the same reason some quick automatic nitrous cars use a converter charge pressure dump circuit- more rpm with less torque multiplication on the hit smooths the torque profile, which in-turn making the car easier to stick. Staggering the nitrous hit to come in on the heels of the inertia discharge also makes sense if you want to leave from hi rpm. One advantage to leaving at hi rpm is the ability to use stored energy for the launch instead of nitrous, so less overall wear/tear on the block/rods/crank from a prolonged lower rpm nitrous hit. Another is it also more closely aligns your clutch tune requirements for launch vs shifts.

My personal focus is radials on zero prep surfaces, smooth power delivery is important. Using one of my Hitmaster 2-stage clutch hit control systems...
...Nitrous is off and the clutch is in it's softer 1st stage mode while the clutch is pulling the engine down on launch and after the shifts.
...Nitrous is on and the clutch is at full clamp pressure while the engine is gaining rpm.
I have a launch timer and separate shift timer for the clutch, also a delay timer for the nitrous. Separate timers for the clutch and nitrous allows playing with the transition overlap between the clutch and nitrous for a smoother profile. This also makes it possible to harness the shift flare from a WOT clutch assisted shift, closing much of the performance gap between clutchless and clutch assisted shifts.

Grant

weedburner

You might not think you are there yet, but optimizing clutch engagement rate is the best "bang for your buck" thing a manual trans drag racer can do. Lots of time/money/frustration gets spent chasing fixes for problems that are basically caused by a car having more clutch capacity than it needs. You have enough clutch to handle nitrous, that's why you are chasing band-aid launch fixes like low launch rpm.

Grant

98cherrySS

iTrader: (2)

I hear ya guy but honestly, I have literally never even tried to launch of the 2 step yet. I'll work with what I have and be alright. The purpose of this post is learn what others are doing in order to launch their 6spd on a 2 step with drag radials. I appreciate your responses.

ddnspider

iTrader: (26)

You just start at a reasonable low RPM on a 2 step and then work your way up until you start to spin. I always left between 4-4500 in my case and it didn't bog, but I was boosted.

TheeCamaroKid

ditch the radials or get a ClutchTamer. I run ET Street Bias and Clutch tamer on my bolt on car, and it has helped with my 60fts....still playing with the tamer, tire pressure and launch RPM which will have to resume next year(gonna get a 2 step and start at 5000RPM and go from there),but i love and absolutely recommend a clutch tamer

SLP IROC-Z

iTrader: (14)

Best 60' ive cut on a radial (275 50 15 mt et street radial 15psi) was 1.58 leaving at 6000rpm with perfect clutch slip that was it for those. This was with full drag suspension, 4.30 gears, 425rwhp, 3500 race weight. Switching to a 3053S 26" MT ET Drag the car cut a 1.54 without even trying and would do so consistently. Then i turned it up to 7200 rpm and cut consistent 1.49s. Radials have to dead hook leaving the clutch to do all the work. Its also very hard to slip the clutch the exact same every pass and wears the clutch faster. The biggest problem is they are not consistent traction wise with a stick. Bias plys can take alot more of a hit, absorbing that energy initially then releasing it. They also don't need to dead hook, they can spin a little initially without completely giving up traction (unlike a radial) which helps the revs not fall as fast which is much easier on the clutch and keeping forward momentum.