How do rev limiters work?

sapper_g · #1 (**permalink**) 10-04-2001, 08:37 PM

How do rev limiters work? I know they are strongly recommended, but I know nothing about where they mount nor what they actually do to limit the RPM.

Thanks,
Glenn

petek · #2 (**permalink**) 10-05-2001, 09:57 AM

From what I understand there are two forms of rev limiters, both start with measuring the rpm (fairly easy to do, just count the number of pulses in a given period of time). Once the rev limit is reached the electronics either:

... shuts down the current to the coil for a period of time, turning off the high voltage to all of the spark plugs.

or ... shuts down the current to the coil for individual spark plugs randomly.

Of the two methods the second is preferred as excess gasoline doesn't collect in the cylinders.

petek

CobraEd · #3 (**permalink**) 10-05-2001, 11:01 AM

I think is has to do with a solonoid activated band that clamps around the flywheel when the rpm limit is reached, . . Not sure though. But I do know that there are mirrors and magnets involved!!!

Ed

CobraEd · #4 (**permalink**) 10-05-2001, 11:29 AM

427sharpe · #5 (**permalink**) 10-05-2001, 06:31 PM

Usually by 'misfiring' cylinders when a certain RPM is reached. I have audio/video of my big block hitting the MSD's rev limiter when I tried to show my wife how to drive it. BTW---downshifting from 4th to 1st is a very bad idea @ speed (but it will keep your wife quiet at home for as long as it takes you to rebuild your transmission!!!)

Brownyard · #6 (**permalink**) 10-09-2001, 07:35 AM

Rev-limiters such as MSD's "soft touch" will allow you to bump up against the pre set (via modules inserted in the limiter) limit without shutting the whole thing down. As previously mentioned, they do so by randomly misfiring the cylinders. Much easier on the motor than the On-OFF approach.

NOTE, a reve limiter will not protect your engine from overrevving on down shifts! That is the more likely way to blow an engine, since it is revved mechanically by the gears in the trans rather than by right foot induced foolishness. A misplaced shift can result in hand grenade motor and there is nothing that a rev limiter can do to stop it.

Rick

CobraEd · #7 (**permalink**) 10-09-2001, 08:02 AM

Not only is there the issue of over reving on a bad downshift, but also, when this happens the crank is yanking on the bottom of the rod caps in effect trying to pull them off the rod as compared to the rods being pushed down onto the crank like normal when under power. Very Bad!!

Ed