2 step timing

i have a blown alcohol bbc 1471 hh retro door car with a powerglide. i have been using an air throttle for staging. i plan to stop using it and start 2 stepping it on the line. i plan on starting out using a leanout with a .120 jet on the 2 step. i usually have to pull 15 degrees of timing to get the car to leave without spinning. is the .120 jet a good starting point and should i leave the timing in it while 2 stepping the motor and have the timing come out at the hit or will it be ok with the 15 degrees out of it while on the 2 step? the main reasons for going to the 2 step is to help out my reaction times and also my fuel pressure drops slightly when the throttle plates open and i feel like the fuel pressure will be more constant with the throttle plates being open at the hit. does this sound correct? thanks

 

i am running the 7730

 

I don't understand why you think the 2 step will improve reaction times when most bracket racers use an air throttle for that purpose. As for fuel pressure, we found if we used NO fuel bypasses till we are into the run, we could use more timing at the hit and the fuel pressure will be higher. Not the best for the oil but the engine liked it a lot. 60 fts went from 1.0's to sub .950's with no traction issues.

 

Unless egt's dictate otherwise there is no need to bleed fuel against the brake. The roots blower needs fuel at the hit anyways, taking it away will only cause premature detonation. If starting line temps are "X" and finish line temps are "Y", keeping that gap as large as possible provides you with a much larger tuning window and ability to build a much snappier tune-up. Leaving with timing that retarded against the brake only raises egt's and cylinder head temperature. While you may not be able to leave at full tilt, find something that will make the car happy. In many instances it isn't that you need to leave with less because the car's spinning, it's more that you left with too much out and as the converter begins to couple the car is behind on wheel speed and in its' attempt to catch up it takes the tire off. A smooth rate of gain with ignition timing is paramount. What kind of shocks are on the car, what is instant center, 4 link setup etc etc..? You'll find a lot in the chassis setup moreso than the engine. Hope this helps, you can email me if you feel I can be of further assistance.

I do believe the 2 Step can assist in reaction times by simply raising or lowering the leave RPM. With WOT against a 2 Step your setup will be much more consistent run to run in various atmospheric conditions, just my two cents.

Brandon Booher
NHRA TAD #3
Torque MGMT. - Owner
217.840.1500
underby6@gmail.com

 

How long before the transbrake releases would you have the throttle blades wide open? I thought sitting on the 2 step with blades wide open very long was a bad idea. I currently use an SLE and a 2-step. Currently my SLE opens about .1 before the transbrake lets go (maybe .2 seconds. I have to go look at my data). The 2-step then just pauses the RPM increase until the transbrake lets go.

 

do you leave with a delay box? how do you know when the throttle control opens in relation to the TB releasing?

i dont mean to get off the topic of the 2step but i have a question that may even help provide more info for other ppl aswell.
What would you be looking for on the EGT's that would tell you that you need to bleed fuel while on the TB?

On our car we leave Wide open on the 2step and our egt's fall in temp untill the release of the TB, Does this indicate to anybody we should pull fuel out? mabye we are pulling so much timing its giving the egt's a false reading in that sence?

 

Sorry - yes. I'm a lowly Top Dragster, not a Top Alcohol Dragster. So yes, we leave off a full tree. Between the delay from both cars staged, to the top bulb coming on, my normal delay box entry, and the fact that we are the quicker car, I can easily be on the 2-step for up to three full seconds. I always thought blades wide open on a 2-step was bad news for that long, so my SLE keeps the blades closed until right before the trans brake comes off.

 

What is an SLE ??...

 

Starting line enhancer..... Let's you stage a car with an air throttle with your foot on the floor. Then open throttle when t brake releases. The trick is to not go down on the throttle until your side of the tree starts down.

 

Well, not exactly. Once the transbrake button is pushed, you can put your foot to the floor and nothing will happen on the motor. When using a delay box with SLE, the throttle will not open until the delay box releases it. You can program that time to be as long or short as you want. When released, the throttle goes wide open(or as far open as you want) and now the motor is on the 2 step. It stays there until the transbrake is released. Its the best way to go when bracket racing in my opinion. In heads up racing it all works the same except you go straight to the 2 step when the throttle is pushed.

 

That's what I meant. You have to wait until you engage the trans brake to mat the throttle, the butterflies don't move unroll you tell them to. I used to run an air throttle and had it open the blades from my stage rpm setting a the release of the trans brake. But last year I ditched the air throttle and all of the associated bullshit and now just two step it on the trans brake same as I used to do my bracket car. However I have never matted the throttle on any car I have had until my side ( on a full tree race dial in deal) of the tree started down. With a fast car you can sit there forever on a two spet if you have to run a slower car. The way I do it it is the same whether I race a car a couple of hundredths slower than me or a whole second slower.

 

SLE, starting line enhancer, consists of two air cylinders, the first controls stage rpm. Before PRE stage, activate the SLE and put your car to the floor, the rise in engine rpm is controlled by how you have set the cylinder( i set mine just a few hundred rpm over idle), then roll in and stage as normal depressing the transbrake button. One second before launch air now activates that first cylinder to bring your up to your launch rpm (determined by throttle blade position). At the release of the transbrake(launch) air activates the second cylinder and brings the car wide open-rate of openning can be controlled by a valve that restricts air entering the cylinder.

SLE's make the whole staging process much easier as you have your foot to the floor before staging-all you need to work is the transbrake button.

Brian

 

i understand the added benefits for the guys that use them but for the time being i see it as just another way to lose a race and il tell you i dont need anymore of them. Our car leaves wide open on the 2 step, no problems so far. using a sportsman tree is pretty easy to just wait for your side if your the quicker car. Pro tree is a little different but we tend to be in the lower have of the field we run with on a pro tree so we arent typically waiting for the other car on the 2 step for an unreal amount of time. If we happened to be #1 qualifier and had to race the slow guy in field then sure it may help but if our class even the fastest to slowest cars wouldnt have a huge amount of wait time. I would hope anybody using or thinking of using one take a look and see if you actually need it. Or if your driver should do a little more driving of the car. Just as added info from what i have read up on these SLE is typically the air cylinder that is supplied in/with a kit isnt big enough . especially if you mount it at the pedal instead of the injector/carb. Much harder for the air power to move a long cable with bends and what not in it then it is for it to just move the butterfly shaft. Again as a disclaimer do not have any personal first hand info of this , it is only coming from what i have read and friends have tried.

 

Thanks for the replies guys, I get it now. Sounds like a good job for a programmable linear actuator or a drive-by-wire servo. Hmmm, I wonder if the rules dudes would allow drive-by-wire?.....