How do you select where it's best to set your 2-step "stutter" RPM vs your Flash speed. from trial and error it seems that Raising the 2 step RPM relative to the stall seems to have the effect of softening the tire hit/chassis reaction but also shortening the roll-out before the converter "hits".

So is it conventional logic that a heavier car (that needs or relies more suspension reaction out of the blocks) seems to favor a lower FB RPM as the tree comes down where as a lighter/ better hooking car favors less of an RPM gap between FB and flash and launches with less suspension "hit".

you guys that race all the time....do you ever Tune the chip RPM to track conditions to get a better launch, and is there any consistent cause and effect you know first-hand from experimenting?

I was, am, and will always be a Stick guy and much more comfortable as a 4 speed racer, and although converter Voodoo seems easy enough to grasp and yet certain aspects seem counter intuitive verses a clutch. Help me get my head around it better, gang!

I footbrake a 7.30-7.40 1/8 car, I run a very loose conv. 5000-5200. I can leave from just above Idle to 3500, makes no difference in 60'. What leaving harder will do is quicken the reaction time. Your results may be different.

Thanks,

Hoping Mr Ultimate (Lenny) will jump in. I remember he tried to 'splain it to me once, I remember him talking about when you are holding at WOT once you apply the load the motor pulls down (drops in initial power) for just an instant (so a realtively softer launch) and the motor will actually produce more initial/instantaneous torque when you hold it at part throttle and roll on the pedal (like with a rev limiter) than it would applying the load to WOT...something like that and I can sort of understand how that happens....

What my mind is trying to visualize is the differences in flow through the Turbine/stator and impellor when the tailshaft is held against the brake at the various launch RPMs.

Mine is a 9.0 foot brake a car. I adjust rpm for reaction time. Converter will flash to 6100, leave about 3000 give or take. It has no 2 step. Car doesn't seem to care what the rpm is for ET. 60ft 1.25-1.27 on a decent track.
Doug

Not an expert, but the purpose of the two step was so you could floor it, then release the button on the top light. If the rpm isn't up enough it might bog since the carb is wide open, no pump shot is left. Normally we tried to get 3000-3500 stepping, with just brakes it would creep, that was the point the TB was needed. Of course depending how loose the converter is it might be a higher rpm, then could be more slippage on the top side. I had a 8 inch 3800 conv. but it would push out of the lights at 3000 so tried using all four brakes on the line lock, then going to the TB. Ended up taking all the buttons,boxes out and staging at 1900-2100 , cut good lights and ran the same times.

I would check what rpm you start skidding the front
tires... thats gonna be the major factor.. the higher
the rpm the closer you will be to your max torque..
a low rpm does hit the tires harder(its wind up that
slaps the conv.. and in a lot of cases will blow the
tires off at the hit... a higher rpm(closer to the stall
is less of a slap to the conv).. on my TB I could NEVER
come off idle.. I had to be up in the rpm to some point

I have a 8 in converter that flashes around 5000 but I can only go around 2900 on the line before it slides the front tires. It leaves harder stalling foot braking as much as I can but it runs the same ET idling or 2900. I can cut a better light the higher I stall it.

I'm curious about hooking my 2 step so I can have a little more consistency and focus more on the light.if I leave higher than 3200 my 60ft is crap so I leave about 2900 with converter flashing to 5400

Your mph is definately soft for that et unless you slightly lifted.......

No I didn't lift that was on a TNT night, those days I usually chase et

Somethings up then.......

At all the tracks I bracket race at (6 tracks) if you use a 2 step you have to run in the Pro class with the guys with Delay boxes and trans brakes. I run in the foot brake class. No electronics at all. Also no buttons allowed (line lock on toggle switch only).

When you go up n rpm.. what else are you changing..
your changing the torque point and the slap of the
conv.. when I go lower on rpm I have to raise the
tire pressure to compensate.. if I go up I lower the
pressure.. being a 4 link I dont have to change that
part.. but if a ladder bar I did have to change the
front of the bars

Same here. Are you running foot brake class using a trans brake and two step?

There are tracks that allow a trans brake in the foot brake class, I race at 2 of them. Never understood why. They both have a electronic class which I guess just lets the racer add a crossover/delay box.

That does not make sense. Why call it a foot brake class and allow a trans brake?

Being that I run a stick car I run in the foot brake class, I figure they have a slight advantage using a trans brake. I probably could eliminate the mechanical clutch linkage and put on a hydraulic slave cylinder with a solenoid hooked up to the line lock . I think that is not allowed at some tracks. Does anyone use that type of setup?

Because its called no box and box.. thats the
way division 3 is.. thats why I have a trans brake
because its legal even in no box

Hardly an expert, but I'll share my experience. My car is a heavy street car, and I've found that it 60's better leaving more up on the converter. 9-1/2" converter, flashes to around 4500, I've been setting the 2-step at 3000, where its nearly a half a tenth quicker than just down at 2500. I also typically don't floor it when its on the 2-step. I get just past the 2-step RPM and hold it there to leave myself some pump shot. Stomp it and let go of the brake at the same time; 2 step is just wired into the brake light circuit.

Common bracket classes up here are sportsman (footbrake, no electronics,, no 2 steps 12.00 floor), Pro (Trans-brakes & 2-steps are ok, floor is 8.00) & Super Pro (add delay boxes & electronic devices).

2-step is not considered "electronics".

My 2-step is triggered off the brake pedal. I have it set at 3000 and it hits the tires hard but my 60's suffer due to the short wheelbase and the (too) high rate of wheelstand. If I understand what Lenny said the higher the launch speed the less violent a light car will hit the tires. Like I said it seems counter intuitive but since you are at WOT you get no torque boost from the (secondary) pump shot.

So....I was going to try 3800 and if that helps, 4200 on a 5300 flash, brake pedal is plenty stout to keep it from rolling through at 3000.

Still hoping Lenny will chime in, I may just need to call him. Again, I'm trying to visualize the fluid dynamics of the converter in those first couple 1/10's of a second after coming off the footbrake.

It's logical that generally the lighter a car is the "tighter" a given converter will be for a given gear (torque multiplication) and the hit would be a bit softer, just trying to get my head around the FB RPM vs launch RPM vs true Flash (full pull)