Racer,

for those of you who leave at a low RPM, activated by a pressure switch in the brake line.

Which switch? part number?
What RPM?
Do you employ the MSD low RPM adjustable chip?
What is your method to disable the switch down track?

Thanks for any help.

NOTE: for foot brake leave

quote:

Originally posted by Larry Woodfin:
Racer,

for those of you who leave at a low RPM, activated by a pressure switch in the brake line.

Which switch? part number?
What RPM?
Do you employ the MSD low RPM adjustable chip?
What is your method to disable the switch down track?

Thanks for any help.

It's been 30 years since I done that & I don't remember everything.

I used the stock brake light switch & it was adjustable from factory (80 Camaro)

1800-2000 rpm

Yes, used the MSD low rpm adjustable chip.

I don't remember it being disabled down track & yes I used the brakes. I think it would be easy to tie into your shifter with a switch & relay.

I used one back in the mid-80's. It was an in-line pressure switch, but I don't remember for what application. I made my own adjustable RPM limit chips (actually an adjustable pre-set switch), usually set around 3000 rpm. I did not disable the switch going down track and I did use the brakes.

Larry, rather than post links to some past discussions on here, I am going to copy & paste from them, to share what I use:

"I recommend a hydraulic pressure switch for reliability. Borg Warner (BWD) P/N S194 is what I have been using on my race cars for over 20 years. 1/8" Male NPT threads, 2 male bullet terminals, N.O. It is very compact, about the size of a small walnut. I mount them in brass Tee fittings close to the master cylinder.
It was the OEM brake light switch on most U.S. vehicles for almost 40 years. Never used by Chevrolet, but it appeared on every other GM brand, (Buick, Olds, Pontiac, Cadillac), plus Dodge, Ford, Lincoln, Mercury, Chrysler, Plymouth, Jeep, AMC, Hudson, etc...
They react quickly, and last forever. I use them to trigger/release 2-steps as well as brake lights. I know Advance has them for about $10, so does Speedway Motors.
O'Reilly sells a Standard Ignition version, SLS27. Haven't tried that one, probably identical or similar. Lifetime warranty, too.
Since the parts stores no longer employ many car/parts guys, just ask for a brake light switch for a 65 Ford F-250 pickup. If they need to know what engine, tell them it has a 352."

"I used a lighted toggle switch on my dash to enable the circuit for the brake line pressure switch/RPM limiter. It was only turned on after the burnout, and flipped off during the run.
Here is why I used the setup: Back when I was running Div V, in the Sportsman ET class, it was considered "No E", (meaning no box/no brake), but you could use a single stage rev limiter: Your choice of whether to use the stage/launch limiter, or the max RPM limiter. (That rule may have changed in the past 10 years). So you could pull your high end chip and use the stage/launch limiter.
I have always staged at idle, then raised the RPM up to launch. It is much easier to stage very precisely at a lower RPM, taking smaller bumps into the beams. After pure footbraking for many years, I could easily bring up my RPM's to within +/- 50 of my target by ear, without taking eyes off the tree to look at the tach. But I always had to aim for a 20 light, (just in case I was a bit high on my launch RPM), to avoid bulbing it. In a game of precision, the limiter was another legal tool that allowed me to shave my average R/T range much closer to .01x-02x."

Hope it helps.

A bit more on my old setup:

"I originally wired mine with fused 12V to the N.O. pressure switch, then ran the switch output to the bright orange lighted toggle switch on the dash, then to the ignition box. So the toggle switch only lit up when there was adequate brake line pressure. That hydraulic switch was super reliable, so I later rewired things to light the switch whenever it was "On". That way it always reminded me to swat it off after the shift, while I was going down track."

Jim, Thank you, all seems just like what I will rig up and test. I appreciate the help.

NOTE: Appreciate = "to recognize the value of"

Jim, be on the lookout next Spring for me at Xtreme.

You're welcome, Larry.
Hope to see you there.
I think they are running brackets May 23rd.

Larry, we used a Hobbs switch. I’ll look at the part number and pressure. We then mounted a micro switch that activates it in low gear only. It does have a Master switch too.
2500-3500 leave.
It’s a brake light pressure switch originally.

I've got the BW S194 switch screwed into a port on my Hurst linelock. I power it with a transbrake button on my steering wheel. After launch I can take my thumb off of the button and there is no power through it so no stutter down track if I scrub the brake. I had a toggle switch but at times forgot to flip it. I've used the MSD adjustable chip and a Shifnoid one, both work fine. RPM I'm 2500 t0 3000

^^^ BP & Eman offering up some good ideas, they are both improvements to what I have on my setup!
Thanks for sharing, guys!