footbrake or 2 step w/holley vac secondary ?

[GallopinGhost]

Looking for some advice. I have a new car, e-body, with a big block and am wondering which is the best method to launch. For consistencies sake I would like to use the 2 step, but I think with the throttle floored I"m missing out on the primary pump shot on launch, and also not sure what the secondary would be doing. The carb is the R4688. I think if flows 725cfm, but I can't find much of any info online. thanks

[Larry Hill]

I run stock with a six pack 440 with 1350 cfm and only one small accelerator pump. It take a little bit of tuning but it works quite well. Been 1.28 in 60' with 3250# car. Don't forget the wheele bars!

[GallopinGhost]

Your car is definitely impressive Larry, I'm not in the ballpark in needing wheelie bars yet. I've only made a couple of passes so far. And on 2 barrels at that. I'll get it figured out.

[Dan Lattimore]

Went through this with Kenny Coonce's A/SA Camaro years ago. Car started to wheel stand after going to two step. With the stiffest spring in the vacuum valve the secondaries are fully closed when up on the two step. When the two step is released the car initially starts to leave on a two barrel with the secondaries steadily feeding in . Kind of like a controlled bog. Fine tuned it with vacuum springs till it carried them out and set down pretty as a picture. Kenny did the same thing to Randy Heer's car ( Kenny's old one ) and Randy stood there in disbelief . Shared that story with Jim and Matt Morgan at Englishtown one year. Shortly after Matt was replacing oil pan and headers on the Mustang.

[GallopinGhost]

That sounds like the standard way to get it to launch on the 2 step. I plan on doing that and get it the best I can with changing the springs. Then see how it likes foot braking it, I've been told it will have the best 60ft. with foot braking. We'll see.

[GallopinGhost]

Thanks Dan. Any idea how far you got the secondaries open on the 2-step ? I heard that to make sure the secondaries don't close any once you launch. the whole 2-step, mash the gas, then release concept is a little fuzzy to me, alot happening in the carb I think

Originally Posted by Dan Lattimore

Went through this with Kenny Coonce's A/SA Camaro years ago. Car started to wheel stand after going to two step. With the stiffest spring in the vacuum valve the secondaries are fully closed when up on the two step. When the two step is released the car initially starts to leave on a two barrel with the secondaries steadily feeding in . Kind of like a controlled bog. Fine tuned it with vacuum springs till it carried them out and set down pretty as a picture. Kenny did the same thing to Randy Heer's car ( Kenny's old one ) and Randy stood there in disbelief . Shared that story with Jim and Matt Morgan at Englishtown one year. Shortly after Matt was replacing oil pan and headers on the Mustang.

[Dan Lattimore]

Brian----This was done on cars that had the best of everything as far drive train ,chassis and suspension. Just get the spring assortment kit and start with something in the middle. Change springs up or down depending on tire spin and how the car feels and reacts. ---- Another tuning tool to get the car down the track.

[GallopinGhost]

Dan, Just trying to find a good ballpark. I will try to get it halfway opened. I should be able to do that in the driveway with a paperclip on the linkage. Testing is great, but getting quality testing done is, as you know, takes alot of time. Thanks

Originally Posted by Dan Lattimore

Brian----This was done on cars that had the best of everything as far drive train ,chassis and suspension. Just get the spring assortment kit and start with something in the middle. Change springs up or down depending on tire spin and how the car feels and reacts. ---- Another tuning tool to get the car down the track.

[Coleydog]

Brian, glad you out racing finally, hoping for the best. On the carb, remember the secondary's work on velocity of air thru the primary's, so if two stepping at around 3000-4000 there might not be enough air flow to pull the secondary's open. Don't forget to restrict the channel branching into the secondary's (better signal). More to come, we'll talk pm

[Dan Lattimore]

Originally Posted by GallopinGhost

Dan, Just trying to find a good ballpark. I will try to get it halfway opened. I should be able to do that in the driveway with a paperclip on the linkage. Testing is great, but getting quality testing done is, as you know, takes alot of time. Thanks

Brian -- PM