Footbrake Race Converter experts - ? on 2 step vs Flash RPM

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)

Lot of good info here, but there are so many variables , it would be quite hard to put them all in a paragraph. What you said in the initial post sums it up well as far as determining how the converter will react as you come up on rpm closer to stall speed taking the multiplication away and hitting the tires softer or leaving at a lower RPM and giving the engine more of a run at the converter resulting in hitting the tire harder. Again, all the variables around the car, especially suspension set up, track conditions, weather conditions, etc will have an effect on the performance of each car,and tuning to the given conditions goes without saying... so many variables. If you want you can call and we can discuss it in more detail.

Thanks Lenny!

I was hoping you'd see this, don't know if you remember talking to me about it but what you just reiterated makes a lot of sense now.

BTW, did you ever see this clip of my buddy Nat's 442" Jeep with your UCC 9 1/2" Converter? This thing drives like a stocker and runs low 12's at 3800+ pounds!! Watch it CRUSH this modded SRT-8 AWD Cherokee.

https://www.youtube.com/watch?v=7bNsxJLSie0

I put my 9 1/2" UCC converter behind my new 440" small block in a 66 Valiant wagon, the 3800 stall should be perfect. The motor will make just a hair more power than the jeep and be about 600 pounds lighter, it's going to be a blast!

What he said falls in line with what I said about slapping
the conv... higher launch has less of a run up to hit the
conv stall point... the torque multiplication is still there
but you dont end up with the free rpm slap

I agree with you completely Mr. P Body

While raising the tire pressure is easier, you could accomplish the same thing by stiffining the shock in rebound. Not as easy as a tire pressure change, but it accomplishes the same thing. Well kind of.

Thanks to everybody, it's a good topic!

Down here there is 2 classes, Footbrake, Any ET.(No delay box,No 2 step,No trans brake, foot brake only) The other class is Pro,Any ET (You can have all the above)

Mine is a ladder bar car it's set in the bottom hole it was in the middle but pinion angle was off..I set tire pressure to track conditions that day.


Here we have Pro and Super Pro classes, 1 allows delay boxes both will let you run trans brakes

I foot braked a Duster running 6.90-7.0 for years
What I found was --looser converter made car faster but....
I could cut way better lights with tighter converter
Stalling it hard as possible also enabled better lights
Once I quit caring about ET and tuned car for best reaction times and best lights it started winning!
Two steps and Transbrakes in footbrake is just like mixing chocolate and [censored]--it is silly--either footbrake the car or put a box in it!
You are fighting city hall
Drum front brakes on footbrake car are a MUST--they are self energizing--they HOLD the car 10 times better than disc--most winning footbrake cars have drums--there are ways are lighten them--been around for decades
Toss the brake or get a box
Brakes are the secret to Foot Braking
Loose super fast converters sink the whole set up
Leave RPM has to be consistent to cut good lights and win races--Period.
I am always amazed that folks are never seeking ways to WIN more races--
rather they fiddle with the mechanical aspects of the game
Those have to be understood for sure so your basic questions are super valid but if you want to win races study the guys and ask the guys that win lots of races --same ole guys win all the darn time and many can't even adjust a shifter--they just have learned How to Win!
Get the car where it will hook in a plowed field and is not so sensitive to track conditions--keep converter on tight side --work with all the things you have available like front tire pressure, shocks, big mirrors, staging technique--never forget the psych game--use it like you have a truckload of it to get rid of fast--Polite drivers do not win--
Then go win a race--amazing thing is after you get one they start to come easier and easier--pretty soon you are the guy they don't want to get beside--then they start beating themselves and you are da Man!

Converter choice should be about tuning car for best lights in a footbrake car--nothing else. ET should be just a result not the goal.

Nothing helps like trying several and just see what happens--you will find a favorite and win like crazy until it blows up--then you will have to buy several more to get another one like it--they are like cakes --same recipe from same baker--top looks different on every one!

I said [censored] like sourkraut how did That get censored--really???

Your little wagon is super duper COOL!!!!

Couldn't have said it better.

We set all our stuff up to leave at the lowest RPM possible and keep the tree green. The convertor stall is more critical to peak power and fall back RPM than anything else in bracket racing.

To me .03-.05 in ET isn't worth it to max out driveline components and not be in the hunt on the starting line setting a car up to need 4000+ launch RPM. Generally for a car to be REALLY good at any track year round you need to be about 3000-3600 off the Tbrake and off the pedal usually 2400-2800, any more than that it will spin somewhere sometime.

I gave up a long time ago giving this advice to racers that are teen and double 0 red at 4600-4800 and do everything but lower launch RPM because "I ain't gonna go out there and run slower!"....who cares? Loose convertors and 4.10 gears are your friend in most door cars. Gives you a big window on the tree.