2-Step in Auto?
Derty I am a slowpoke so forgive the ignorance. What if you have a converter that brake stalls at 3200 rpms. Lets say it builds 3 psi that way....would a 2 step set at 3200 rpms not enable you to build maybe 5psi or so? I don't know how much boost builds with brake stalling. Hopefully this will be an educational thread 
The Bull
Joined: Jun 2002
Posts: 3,578
Likes: 2
From: Grand Rapids, MI
Wouldn't matter, a 3200 stall converter will stall at 3200 on a transbrake if that's the correct advertised stall speed. For instance my converter stalls at 4000. On the brake it is exactly 4000 RPM no higher or lower. You will likely build the same amount of boost, maybe a tad more, on the brake rather then alternating/missing sparks to attain that RPM. Basically the two step sacrifices power to maintain a desired RPM. It takes that power to spool up a turbo or provide the power to spin a blower. A trans brake doesn't sacrifice anything, so you'll leave with the most amount of power and no transition from intentional misfire to rolling. My 60's are consistently faster off the brake rather then off the 2 step at the same RPM. Granted, I'm don't run a forced induction car. But you can look at just about everyone else.
The only other reason I can think of that you would run a two step is if you wanted the RPM to spool up at a speed lower then the stall speed. There are many reasons why you might want to do this. For instance the car just leaves with too much power for the tires. We do this with a Pro Street car that I crew for. All the torque and horsepower from the big block is too much for the tires (~1500+ HP NA!). So the MSD ignition is backed down below the stall speed just a bit. We even have to run a .1 second delay for the nitrous to make sure that the tires plant before spraying it so that we don't overpower the track. We get a lot better results that way.
The only other reason I can think of that you would run a two step is if you wanted the RPM to spool up at a speed lower then the stall speed. There are many reasons why you might want to do this. For instance the car just leaves with too much power for the tires. We do this with a Pro Street car that I crew for. All the torque and horsepower from the big block is too much for the tires (~1500+ HP NA!). So the MSD ignition is backed down below the stall speed just a bit. We even have to run a .1 second delay for the nitrous to make sure that the tires plant before spraying it so that we don't overpower the track. We get a lot better results that way.
ahhhh....makes sense. Anyone tried a 2 step on an auto? Based on the principal of how the 2 step builds boost, I'd have to think that you build more boost with the 2step than without in an auto. Hopefully someone will chime in who has one on a turbo car and an auto. I see what you are saying about lowering rpm for traction...that is a good enuff reason to keep mine
Don't forget the fact that your stall speed will go up as you build boost. If memory serves, stall speed increases with the square root of torque.
the harder you stall against the converter, the more boost you make, the higher the stall speed is, the more boost you make, etc etc.
You get the picture
the harder you stall against the converter, the more boost you make, the higher the stall speed is, the more boost you make, etc etc.
You get the picture
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I like the idea of the two step so you can launch at a consistant RPM with out having to watch the tach. Concentrate on the lights and be more consistant with your dial and ET.
TECH Addict
Joined: Feb 2002
Posts: 2,319
Likes: 0
From: Lewisville, Texas
I use Matts 2 step with my brake so that I can launch at the stall speed of the converter(3800RPM) and have the nitrous engage as soon as I let off the brake. My lower pill is a 3000RPM pill so If I didn't use it as soon as I hit 3000RPM on the brake the N20 would engage, not good sitting at the tree. I could have gone with a 4000RPM pill but then I would have had a 200RPM dead band before the N20 hit and I wanted it to hit immediately when I let off the brake.
