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Need An Education On Rev Limiters

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RPMx100

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Discussion starter · #1 ·
I've done a search and read about rev limiters on other threads, but I need an explanation on how they work. (Have never seen one, or been in a car that had one)
1. Say it's set at 6000. When you hit 6000, does it die off or mis-fire alot, or continue spinning smoothly at 6000 and no more?
2. The MSD model (I want a direct replace HEI-type module) says something about "Traction Control Detection"...Does that mean it'll fall on it's nose during burnouts like new cars do when spinning?

Have been waiting on something without a big ignition box, and it looks like the MSD unit at Summit is it, but the on-line info doesn't answer my questions.
Thanks!
 
#2 ·
as i understand it the traction control device is some electronics that are hooked up to the front and rear tires that looks at tire rpm. the device limits the rear tire speed so that the rears dont overrun the fronts. this is illeagle in some forms of racing so MSD installed a circuit to kill the engine if it detects it. THIS WILL NOT HAPPEN IN YOUR CASE, if you do not have a traction control device. as far as limiting the limiter kills cylinders in a round robin way. the cylinder will fire on one cycle and then wont fire the next cycle. this prevents plug fouling. its the same system i run on my 496. Dave
 
Discussion starter · #3 ·
Thanks for the explanation sheetmetal!
Mine is a 375hp 396 with low gearing that tachs up fast. Can't believe I've waited this long to get one. Not to over-analyse this, but are you saying with the pedal mashed it'll level off somewhat smoothly at the rpm setting? No whiplash-effect or crank stress?
 
#4 ·
I run the HEI module also. It doesn't level off like a governor and it doesn't shut down like a new car. It studders missing every other cylinder. I run into mine quite a few times and it doesn't pop or back fire or anything just feels like a bad miss.
 
#6 ·
I was looking at the HEI module with the rev limiter and "traction control" also. How does the traction control work here since there is no wheel speed sensors or anything like that?
 
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#8 ·
69-CHVL said:
I was looking at the HEI module with the rev limiter and "traction control" also. How does the traction control work here since there is no wheel speed sensors or anything like that?
Click to expand...
I think some of them look at what they call "slew rate". It doesn't use any wheel sensors or anything. Basically, it looks at how fast your engine is accelerating through the rpms, and has an adjustable limit. If your tires spin, the engine will accelerate faster than if they're hooked. This is where the electronics help, by limiting the engine from accelerating as hard once you hit that acceleration limit. Theoretically, if you set the slew rate correctly for your combo, it will keep you from blowing the tires off, ,and not hinder performance once the tires are hooked. You could probably set it to allow a little wheelspin too, ,if that works better for your car.

I don't know anyt5thing about the HEI one you are talking about though.... the description of how electronic traction controls for old cars work was something I read a couple years ago. It makes sense, and I can see how it could work. If i only had more $$ :)
 
#9 ·
bulb122 said:
I think some of them look at what they call "slew rate". It doesn't use any wheel sensors or anything. Basically, it looks at how fast your engine is accelerating through the rpms, and has an adjustable limit. If your tires spin, the engine will accelerate faster than if they're hooked. This is where the electronics help, by limiting the engine from accelerating as hard once you hit that acceleration limit. Theoretically, if you set the slew rate correctly for your combo, it will keep you from blowing the tires off, ,and not hinder performance once the tires are hooked. You could probably set it to allow a little wheelspin too, ,if that works better for your car.

I don't know anyt5thing about the HEI one you are talking about though.... the description of how electronic traction controls for old cars work was something I read a couple years ago. It makes sense, and I can see how it could work. If i only had more $$ :)
Click to expand...
Chris got it right.
Its more of a engine rev speed limiter. You set it to something like 1000RPM per second and if the engine exceeds that rev rate, It cuts cylinders randomly until the rev rate slows.
I've seen the same type of thing on EFI cars that cut fuel flow to slow rev speed.
 
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#10 ·
The MSD Module that fits inside the HEI in place of the original module doesn't appear to do it in that manner. There's no setting to adjust other than the rev limit.

This per the MSD Instructions on this particular module: http://store.summitracing.com/partdetail.asp?autofilter=1&part=MSD-83645&N=700+115&autoview=sku

"TRACTION CONTROL DETECTION
The Digital HEI Module has a unique Traction Control Detection (TCD) code built into its microprocessor. This technology carefully monitors and examines the signals of the ignition. If the TCD determines that any signal has been modified in any way, the ignition will be put into a low rpm rev limit mode to immediately slow the car. Before this rev limit is imposed, the TCD goes through a list of cycles and checks to qualify that the trigger has been modified. There is no way to bypass or deactiviate the TCD circuitry."

Before I bought mine, I called MSD and they told me it won't have any effect if I didn't have traction control on the car. Not sure how it determines if "the signal has been modified", but this particular module's TCD circuit should not have an effect on our cars.
 
#11 ·
Mark. It looks like MSD has put a detector into there module's to keep people from "cheating' By trying to use traction control. This is the full explanation from MSD.
I believe it will stop your engine from reving fully if it detects a TC device in use.
In the majority of racing sanctions and classes, traction controlling devices are
illegal. MSD has never produced a traction control - and while it remains illegal, never will produce one. What we have designed is a code that will detect if an electronic traction control system is used with an HEI.
This Traction Control Detection (TCD™) technology carefully monitors and examines the signals of the ignition. If the TCD determines that any signal has been modified in any way, the ignition will be put into a low rpm rev limit mode that will immediately slow the car. Before this rev limit is imposed, the TCD goes through a list of cycles and checks to qualify that the trigger signal has been modified.
Click to expand...
 
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#12 ·
Jebchevelle said:
wow thanks I was wondering how they work aswell Iam looking at the procomp 6al box with built in rev limiter.
Click to expand...
=
I would highly recommend that you keep looking :D
But if you really want to try one of these I have a brand new one around here somewhere I will give you a hell of a deal on
 
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