Go Down

Topic: Car rev limiter (Read 2 times) previous topic - next topic

CoolJ

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.

nitrolx

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)?


drother


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.

PeterH

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.
I only provide help via the forum - please do not contact me for private consultancy.

drother

#9
Aug 08, 2012, 12:01 am Last Edit: Aug 08, 2012, 12:02 am by drother Reason: 1

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.
http://www.youtube.com/watch?v=xqeo48caBxs&feature=player_embedded

Go Up