Don Terrill’s Speed-Talk

Anyone know what RPM limiting devices they use for launch ( staging ) in Pro Stock or Comp eliminator?

Is everyone using something that operates like a 2 step?

I used a Dyna400 (2-step) in my son-in-law's sedan, but that's just coz I had a shed full of bike bits!
I'm curious to know what you guys use over there too, some of our racers in sedans have just started using them in the last couple of years or so.

Well , I guess
a) no body knows
b) this is a dumb question
c) Pro Stock and Comp eliminator are so "gaurded" even rev limiters are top secret
d) LMAO

I would imagine they use the MSD boxes like 7AL-3 or the Digital boxes.
They have the rpm limiters built in.
Probably control the shift light rpm also.

JMHO.

I guess I should have asked also.................is there a better device to hold the RPM at launch that is easier on the engine that controls the misfire in some different fashion that just makes it more engine friendly?

joespanova wrote:I guess I should have asked also.................is there a better device to hold the RPM at launch that is easier on the engine that controls the misfire in some different fashion that just makes it more engine friendly?

Answer: standalone EFI box used to control ignition only. Make sure it's one that allows you to tune the randomness of the spark cuts. For example, on our Megasquirt box, we can tune "X ignition events randomly cut from every Y total ignition events" - so, say you can cut 7 sparks out of 10 randomly. That makes sure you're not beating on the same cylinder all the time.

If you add the fuel control, you can set up even *nicer* rev limiters. Some of my Drag Week customers set their launch control limiters up with both fuel and spark cut, which makes for a nice, smooth, no-popping/banging rev limit that's easier on the engine.

Some will argue that the MSD rev limiter "isn't hard on anything" but I can show you a Cup Car driving school chief mechanic who swapped out the MSD rev limiting for a standalone EFI control box (that only runs ignition) on ALL their cars because allowing students to run full laps around a course bouncing off the rev limiter was killing their Chevy crate engines extremely quickly. Problem was solved with the upgrade.


-Scott

joespanova wrote:I guess I should have asked also.................is there a better device to hold the RPM at launch that is easier on the engine that controls the misfire in some different fashion that just makes it more engine friendly?

From my own personal experience, I have never used a Two-Step, just a rev limiter.
Have seen too many engines hammered by a Two-Step...therefore my solution is a good quality tach with a big display and lots of practice.
When you get to know your car well, you can tell by the sound and just by glancing at the tach when you reach the sweet spot for launching your car.

Pro Stock in NHRA uses a spec MSD box.

While I don't think any rev limiter that drops cylinders is an ideal tool, I seriously doubt that just a rev limiter like that is killing engines. There are simply far too many cars using them with no failures. Certainly, if you sit on the line indefinitely "on the chip", you're not doing the engine any favors. A reasonable amount of time doesn't seem to cause any problems by itself. It's usually when there is another problem that the two step aggravates where you see something bad happen.

One thing I do not like, and will never do, is use them in the water. I agree with David Reher when he says that doing that is exceptionally destructive. I count myself as doing a really bad job as a driver if I even hit the burn out chip while in the water.

Daytona Sensor has a system, by the way, that allows you to set your launch RPM, and shows you that you are there with an indicator light. This eliminates the need to look at the tach, you simply push the throttle until your stage RPM light is on, then you mat it and release the clutch or brake to leave. It is ideal for "no electronics" classes.

Thanks guys...........these are the types of answers I'm looking for.

Alan , as you may have guessed , I'm not leaving anything for chance. If I can determine the 2 step was part of my problem , obviously it goes.

Answer: standalone EFI box used to control ignition only. Make sure it's one that allows you to tune the randomness of the spark cuts. For example, on our Megasquirt box, we can tune "X ignition events randomly cut from every Y total ignition events" - so, say you can cut 7 sparks out of 10 randomly. That makes sure you're not beating on the same cylinder all the time.




-Scott[/quote]
I am using the megasquirt on my carbureted pulling truck for ignition control and rev limiter.Also works great for datalogging.

joespanova wrote:Thanks guys...........these are the types of answers I'm looking for.

Alan , as you may have guessed , I'm not leaving anything for chance. If I can determine the 2 step was part of my problem , obviously it goes.

Like Alan said, Pro Stock and most Comp Eliminator engines use the MSD "soft touch" rev limiter.

I've used it on a varity of engines including large naturally aspirated, blower and nitrous engines with out issues.

The rev-limiters that are not of the "soft touch" type can be more harsh.

Blessings............Ron

Ron Clevenger wrote:
Like Alan said, Pro Stock and most Comp Eliminator engines use the MSD "soft touch" rev limiter.

I've used it on a varity of engines including large naturally aspirated, blower and nitrous engines with out issues.

The rev-limiters that are not of the "soft touch" type can be more harsh.

Blessings............Ron

Currently I have a 2 step..........I'll have to call MSD to see if this is the same thing as a "soft touch".

Thanks

and hopefully you reach a good tech, not just some punk in front of a computer screen

I would trust the advice on here more, didn't a few say 2 steps can cause problems?

I think some have said they have had problems while hitting the 2-step during the burnout, or while setting the launch revs too low.
From memory it was to do with holding the engine at a resonance point for the bottom end, so revs will be different for every engine.

Most of the new electronic ignitions that MSD produces come with the "Soft Touch" rev control.

"When the engine reaches your set rpm, the Soft Touch circuitry kicks in and drops the spark to certain cylinders. This limiter produces very accurate and smooth, backfire-free rev limits."

I use the MSD "soft touch" rev limiter on my own personal race car. It's used on the starting line, burn out control and high end rev limiter.

It's use on the starting line and burn out (7000 rpm) works flawless with no detection of any issues to the engine.

The only time I have caution is on the high end use. Once when we broke an transmission input shaft at close to the top of low gear it went on the high rev limiter (8800 rpm) longer than a normal touch. A blower motor is not happy with that. Didn't hurt the engine but the blower was damaged.

Hope that helps..............Blessings..............Ron.