Steven6282

I've got a basic MSD distributor on my car right now, vacuum / mechanical advance, no computer involved.

I'm thinking about making my own rev limiter, partly for a fun little project to do, partly because I've spent way to much money on the car the past couple months and have all the stuff laying around that I would need to build the rev limiter already.

Anyway, in theory I know how they work, they just prevent spark plugs from firing. With the more advanced ones on injected engines also being able to prevent gas from being injected and such. But since I have a carb I don't have that option to stop the gas from being let in.

So my question is on the rev limiting methods. The simplest method for me to create would be just cutting power to the coil and preventing all spark plugs from firing until the revs drop back down a little or for a set amount of time. I read on some other websites that newer rev limiters prevent random spark plugs from firing so that gas build up isn't as hard on the engine.

My question is just how much of a problem is that gas build up going to cause doing it where I just disable spark to all the plugs? I mean I'm not going to be sitting there against the rev limit for extended periods, it's mainly to keep me from accidentally over revving when autocrossing and not having time to look down at my tach. I may also even incorporate a shift light into it if I want to get fancy.

Another related question, I haven't actually looked at it yet, but I'm assuming the tach wire works off pulses? I'm guessing it's simply 1 pulse per round, most likely having a metal contact point in the distributor cap that gets hit to make contact and create the pulse?

Apeiron

The tach wire is connected to the ignition primary, it sees the coil voltage there.