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I want to build a rev limiter for my car, and it uses a logic level coil input from the pcm. If I did my homework right, I would use a PNP transistor. Also, I would set the Base to pull down resistor, so that for some reason if the arduino fails, the transistor would default to "on" to let the coil fire.

The logic level coils like this: as soon as it sees a +3-5V logic input, it begins charging the coil. It fires as soon as it loses the +5V input.

Am I correct that I will use a PNP transistor?
Also, it draws around 40mA. What would be a good transistor to use?
« Last Edit: July 26, 2012, 01:06:56 pm by drother » Logged

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I know this is my first post. I wouldn't normally answer a question on a forum with a first post.
 However, I have unique knowledge in this area. (I have done it)
It was for traction control using front wheel speed vs rear wheel speed. Slightly different application, same outcome.

I tried spark cut first because it was easy with the ignition setup used in the car at the time. The results where undesirable and sloppy.

Spark cut is a terrible way to rev limit the engine. You have an Arduino. You can do better.

Put in an up stream flapper in the intake. You can easily move it with a servo. Center bias the flapper so it can not get sucked closed.
Failure mode = OPEN.

Track engine RPM(several different ways). When the RPM reaches the limit, close flapper whatever amount you are happy with.
This will work for all fuel injected cars Alpha-N or Speed Density. **DO NOT DO THIS IF YOU USE A CARBURETOR**
You have been warned. I wash my hands. smiley-twist
« Last Edit: July 27, 2012, 07:22:37 pm by CoolJ » Logged

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I know this is my first post. I wouldn't normally answer a question on a forum with a first post.
 However, I have unique knowledge in this area. (I have done it)
It was for traction control using front wheel speed vs rear wheel speed. Slightly different application, same outcome.

I tried spark cut first because it was easy with the ignition setup used in the car at the time. The results where undesirable and sloppy.

Spark cut is a terrible way to rev limit the engine. You have an Arduino. You can do better.

Put in an up stream flapper in the intake. You can easily move it with a server. Center bias the flapper so it can not get sucked closed.
Failure mode = OPEN.

Track engine RPM(several different ways). When the RPM reaches the limit, close flapper whatever amount you are happy with.
This will work for all fuel injected cars Alpha-N or Speed Density. **DO NOT DO THIS IF YOU USE A CARBURETOR**
You have been warned. I wash my hands. smiley-twist

Sorry, but not using it for traction control  smiley-razz

I need it because my factory PCM has only a fuel cut rev limiter. I'm adding boost, and need a rev limiter since I will be adding water/methanol injection, and if it was still injecting and the PCM cuts fuel, that could be destructive.

Also a 2/3 step rev limiter for drag racing will also be used (this will be on a turbo car).

Also, one of the world's fastest traction control systems uses merely 2 stages of timing retard for traction control....
http://www.moretraction.com/
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Just a reply so I can follow this one.

Duane B

rcarduino.blogspot.com
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Once my P channel transistors come in, I'll test it with some LEDs.
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I would have to say that my idea is probably not the best if you are using forced induction. Lots of ways for that to go wrong then. I can say it worked perfectly for traction control for my old Camaro on the wet roads here. My rev limiter was my right foot. Next time you should probably note the conditions of your application a little more clearly.
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What car/engine?
What sort of ignition system is in the car?
Is it single coil with a distributor, or individual coils per cylinder?

Knocking out spark to a single coil is pretty rough. . it gives the rev limiter very harsh operation.
Racing ignitions will generally alternate which cylinder they drop, and then make sure that cylinder is fired on the next compression stroke so as not to load up that cylinder with fuel.

The difference is night and day with a digital MSD style ignition limiter to an older 6AL style analog box.
I've run both (in an 8 second carby car) and the digital one is so much smoother, sounds a lot nicer on the engine then the older style.

Fuel cut rev limiting in a boosted application probably doesn't sound great to me either (unless it's a diesel), as it's going to cause a very lean-burn situation in the cylinder it's dropping fuel to (assuming fuel injected?).

Maybe there's an aftermarket option for the computer in your car to allow different RPM limits (for your 2/3 step)?

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What car/engine?
What sort of ignition system is in the car?
Is it single coil with a distributor, or individual coils per cylinder?

Knocking out spark to a single coil is pretty rough. . it gives the rev limiter very harsh operation.
Racing ignitions will generally alternate which cylinder they drop, and then make sure that cylinder is fired on the next compression stroke so as not to load up that cylinder with fuel.

The difference is night and day with a digital MSD style ignition limiter to an older 6AL style analog box.
I've run both (in an 8 second carby car) and the digital one is so much smoother, sounds a lot nicer on the engine then the older style.

Fuel cut rev limiting in a boosted application probably doesn't sound great to me either (unless it's a diesel), as it's going to cause a very lean-burn situation in the cylinder it's dropping fuel to (assuming fuel injected?).

Maybe there's an aftermarket option for the computer in your car to allow different RPM limits (for your 2/3 step)?



Its a 2000 Camaro with an LS1, 8 individual coils. Stock ignition (retty powerful coils, good for ~1000RWHP or so)

Yes, my goal is to make sure when it drops a cylinder, the next cycle it fires.

Basically my goal is to replicate this:
http://www.summitracing.com/parts/MSD-8733/
for much cheaper, and many more features. And of course for the DIY experience.
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You definitely don't want to use timing retard for traction control on a big engine, it'll cook the exhaust valves.

You also don't really want fuel cut on anything with decent specific power because it'll run lean before and after the missed injection cycle.

A spark cut with a walking pattern works great in my experience. You can make it progressive by varying the proportion of missed sparks. Unless you have hugely excessive power and a driver who can't hear the engine you may find you only need to drop a single cylinder, because (ime) the roughness is easily detected and the driver soon learns to recognise that as a cue to feather the throttle. If that doesn't work and if you want this to control power for longer than a fraction of a second it'd be better to fit a cable stretcher rather than run with a misfire.

If you do use spark cut on a high power engine you might want to set up your cut pattern to alternate exhaust headers because the unburnt air/fuel is going to go up in the header and you don't want consecutive cuts in the same header if you can avoid it.
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You definitely don't want to use timing retard for traction control on a big engine, it'll cook the exhaust valves.

You also don't really want fuel cut on anything with decent specific power because it'll run lean before and after the missed injection cycle.

A spark cut with a walking pattern works great in my experience. You can make it progressive by varying the proportion of missed sparks. Unless you have hugely excessive power and a driver who can't hear the engine you may find you only need to drop a single cylinder, because (ime) the roughness is easily detected and the driver soon learns to recognise that as a cue to feather the throttle. If that doesn't work and if you want this to control power for longer than a fraction of a second it'd be better to fit a cable stretcher rather than run with a misfire.

If you do use spark cut on a high power engine you might want to set up your cut pattern to alternate exhaust headers because the unburnt air/fuel is going to go up in the header and you don't want consecutive cuts in the same header if you can avoid it.


This is going in a drag racing car with a transbrake (and remember, turbo car).

1st limiter will be on the foot brake, floored (low enough rpm to not drive through the brakes).
2nd limiter will be on the transbrake, floored.
3rd limiter will be the max rpm, engine RPM should never exceed this limit.


as far as timing not working, as I said, it is being done today by some of the fasted heads up drag cars. It's not like its on for long, usually only a few tenths of a second at most.
« Last Edit: August 07, 2012, 05:02:45 pm by drother » Logged

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This is going in a drag racing car with a transbrake (and remember, turbo car).

Ah. My experience comes from engines with hundreds of BHP that run for tens of minutes, rather than thousands of BHP that run for seconds. smiley
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Has anyone made any progress on a rev limter for a car, I'm also looking for quick ignition cut system for when a car misses a gear change
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Yes, would like to know if this ever got anywhere. Trying to do the same thing.
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My first thought was place a brick under the gas pedal smiley-cool
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My first thought was place a brick under the gas pedal smiley-cool

No, that is called a governor.  smiley-wink
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