fast? about trans brake and two step fuel spike


New Member
Aug 20, 2002
wher do i need my closed look enabled at high and low settings if i am leaving at 3600 rpm on trans brake. i have it now at 1900low and 2400high and i do some driving and does fine, but if i leave on brake on the spray it will spike rick at first. also how close can you run your nitrous enable rpm compared to your two step rpm. my is 200rpm diff now but has a slit delay in it would like to leave closer is this a option?
You can't be running closed loop on a two-step. The O2 will read 15.94 and cause it to add as much fuel as it is allowed. You have to set your high closed loop rpm above your two step rpm. You can set the low rpm to below that rpm if your car pulls below that on gear changes. On a street car you really need two tunes one set with the rpm limits set normal so you get the best possible gas mileage and one for racing when you will be using the two step.
We've always turned closed loop on at 2000 and then 2 stepped it at 3500-4000rpm with no issues. Done that on at least 10 cars over the years.
Have you ever logged it to see what is going on when you two step it in closed loop? What are your correction limits and target air/fuel there?
I'm looking at a log now. 2 stepping it at 3800. Target of 12:1. Actuall of 12.2:1. 02 is correcting -3%. Once I let go of the brake, it's about 1/2 point rich(which actually works out well on a 1000ft lb motor on 10" tires), then catches back up in 1/2 second.
You are one of the lucky ones Shane. Rev limiters typically throw the wide band into a tailspin, but there are a blessed few who don't seem to have this problem.

We typically recommend that the closed loop high RPM is set above the two-step RPM for this reason.

A lot of people will set the nitrous RPM just below the two step RPM and have the transbrake wire trigger a relay that interrupts the 12V signal to the nitrous enable wire. That way, as soon as the brake releases the nitrous turns on.
I know Craig. Everyone always tells me that, but I've got three cars I'm working on right now that it all works great on. I've got very similar programs for them all, though. In fact, we've done at least 10 of these cars with VERY similar setups and very similar programs that all came from the Murillo tune on my car three years ago. They all seem to work identically. I'll take luck any day. :)
thanks again craig and other members for help so craig how close do you recomend the nitrous activation from the two step if i were not to trigger with trans wire? i believe i now how to wire that way, can you please run it by me if possible to be sure? i brake at 3600 so were would you put the high and low for best results if i was not to trigger w/ brake, and if trigger w/ brake how much lower than 2 step to set nitrous enable, and high and low settings. thanks van
Originally posted by NoSlix
I'm looking at a log now. 2 stepping it at 3800. Target of 12:1. Actuall of 12.2:1. 02 is correcting -3%. Once I let go of the brake, it's about 1/2 point rich(which actually works out well on a 1000ft lb motor on 10" tires), then catches back up in 1/2 second.

If I had an O2 sensor that didn't see multiple misfires as a lean condition I would definately be concerned.

Would you please give your opinion on how you think this is possible, Shane?:cool:

I guess one thing I should clarify is that I'm on the 2 step for only 1 second generally, so that may have something to do with it. I do see the o2 catch it, but I guess it's quick enough that it doesn't really matter.
I was looking for something waaaaay more technical than that, Shane. ;)

Here I am up way past my bedtime and I had a thought about this.

Some cars are chipped just below where their converter would sit anyway without a 2 step. If the converter is already presenting a good load on the engine, the MSD doesn't have to kill as many sparks to limit the RPM. The fewer dropped sparks, the less severe the O2 error would be.

Just a theory.
LOL, Jon Dell. Dude, I don't know why it works. It's magic or something. Actually, I like Craig's theory. We'll have to do some experimenting on Big Strong Tony's car here in a week or so. I don't know where he turns WB control on in his setup, but I think we'll have to try a few things out.
Any chance you have the VE cells where you sit on the brake set rich, so that with the misfires from the twostep the O2 sensor sees the afr as back where you started before the misfires started? Guess that would show up on the plugs if you put the motor on the two step and then shut it down to look at them. Would also mean too rich for excellent spoolup, probably. Oh well, just a thought :).
I'm thinking craig hit the nail on the head.

I also think you could take it one step further and factor - in boost. If you hit the chip and the boost begins to rise (as it generally does), that will cause the limiter to drop more sparks and the un-fired cylinders will be packed with far more "unconsumed oxygen" than they were at low boost or no boost.

On a similar note, I think it would be fair to say that a marginal ignition system will make a liar outa yur WBO2 :D