Technical Mechanical Rev Limiters--who's used one?

I have an old Mallory dual point tach drive distributor, and a Jones (Moroso) tach in my Chevy II. The car has no electronic stuff in it, and I want to keep it that way. I got hold of an old RPM activated switch, which I might install as a rev limiter. I ordered a cable splitter, waiting for it to arrive. The unit has a micro switch in it, with C, NO and NC connections. The RPM range is 3000 and up, which looks right to me, since the tach cable turns at 1/2 engine rpm.

My big question is, with a blower motor, if this thing cuts off the ignition at 7000 rpm, how serious is the explosion/backfire when rpm drops and it lights up again?

 

Interested to hear the answer as well. I'm working on a blown build with an external coil vertex mag. I have a 5309 Pro Control box for its rev limiter ability with a mag. It utilizes an inductive trigger to inform the box of engine RPM. The N.O. terminal grounds out the coil when triggered. I know your switch and this box are not the same but they are accomplishing the same goal and would be connected to the mag the same.

I have the 5309 box which kills ignition for a short time and then restores it after RPM drops. The 5305 (internal coil) or 5306 (external coil) has a reset button that must be physically pressed to restore ignition just for blown engines.

I'd like to have the reset button model but I'll keep what I got and tuck it out of sight. If significant damage is an issue I might have to rethink that though. Interest to hear what you find out.
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Jim,
Ideally you don't want it to cause your motor to "slow down" you want to make it lay down on a couple of cylinders. That way you are not actually shutting it off and lighting it back up again.

I don't think that your pop is going to be in the intake anyway, it should backfire which may cause your mufflers to launch.

 

You should set the RPM limit to save engine damage..... not your driving style. [unless you use it to powershift]

If your engine turns to 7000RPM on the track , set the limit 800rpm higher. You should never hit he limiter at all

 

I'm thinking the explosion/backfire would somewhere near epic.

Even with electronic rev limiters dropping random cylinders with a blower can be bad when it drops the same cylinder a couple times in a row. I am used to dealing with alky/blower/mechanical injection and upwards of 3000 hp so my thoughts may be way out of line though.

One way to find out, shut it off right before the finish line, wait a second and then turn it back on.........

 

like PNbean said its not going to pop in the manifold as the valves will be doing there job , but in the pipes . and its going to be loud .

 

I don't want to actually hit the rev limiter, it's a just-in-case thing. I would probably set it for 7200, and I usually try to shift by 6200 or so. I also never rev it anywhere near that high when the mufflers are on the car (ie on the street), so that should not be an issue.

I have a flaky shifter, which I might try to redesign to make it more reliable..but I've hit neutral a few times while racing, and I don't really like the feeling!

 

LOL I got a Mr Gasket ratchet for ya.

I have used mechanicals on fleet trucks. I had a Kenworth with a 318 Cummins that I was taking care of once. It had a habit of the getting the rack stuck open. I couldn't figure out what the problem was and it was getting too pricey for the boss's (and mine) comfort. I finally put a governor (rev limiter) on it and that cured it. I guess it was driver error.

 

I'm the first to admit I want this thing because of driver error!

 

Well you are force feeding a 427 things could get real crazy a lot faster then my natural breather for sure.

The older I get the more I feel a need for a neutral lockout.

 

Sounds like a B&M shifter to me. I used to be relentless on my Mopar bro who had one in his street racer and had the same thing happen all too often. Told him he was the only guy I knew that could miss a shift in an automatic. Then I did it once in my bracket racer with a Hurst. Went from 1st to 3rd at the shift light, but that was when I got it sorted and it started to 60' right. I wasn't ready for that feeling going from 1.70 60' times to 1.40-42. It's amazing how long 1/10 of a second is, isn't it?

 

Um, Big Bang Theory.....

 

I would bite the bullet and get an MSD 6AL. You can use your points to trigger the MSD and keep your cable drive tach. The MSD randomly stutter steps the limiting function to keep you from blowing the supercharger onto the track.

I know the no electronics is a big thing for you, but I won't tell if you don't....

-Abone.

 

?? "flaky shifter, which I MIGHT try to redesign" first thought is that this is a comment about the driver-Ha! before worrying about rev limiter, I would go back through anything that might be the cause of getting to the point of needing a limiter

 

No electronics, sorry.

In addition to driver error or lousy shifter design, there are probably a few other reasons to have a rev limiter.

btw the shifter is one I made, it's sort of a copy of the first B&M shifter for the TH400...which doesn't seem to exist anywhere except in one old picture.

 

As I recall from the pics it resembles the old B&M gated shifter for a hydro. maybe I am thinking about something else.

Groucho has one of these that could be gated for the turbo 400 easy enough. But it would not have the look you are after I don't think.

You are correct though more reasons to have a rev limiter then just a missed shift.

 

that's the 1967 shifter, but I'm stuck in 1966.

 

What's a year between friends....

 

LOL I hear ya. I got 3 shifters in the garage, my current build is as though I was a young man in the early '60s building a hot rod. One fits the era perfectly but it is not what I would call a performance shifter. I am tempted to just drop the ball and use one of the others.

 

that's the problem with building a car for yourself....not many guys get it.

 

I decided to put an overdrive in the car, and had to do some work to the shifter to make that happen. So I made a new gate plate for the shifter, as well. I had to change the shift lever to make it smaller diameter, so it would work with a notched gate. So far it looks like it will work, although I haven't taken it for a drive yet...still more work to do to clean things up, and get the new driveshaft in, etc. The shifter is shown upside down, but that lets you see the new gate for 3rd gear. It has a little notch to keep it from being easy to shift into neutral accidentally.



And I'm slowly working on getting the rev limiter parts together. I'll probably install it.


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how complicated things can get when you deviate from stock...

 

Jim are you running a "Switch Pitch" torque converter in the 400?

 

That's off an old Diesel? like a Detroit? I don't remember where they drove from but its not the crank , you may be limiting to the RPM's on the plate, should be something you can change though. Another way is the RPM limiting rotor buttons.....

 

jim i have run several kinds of rev limiters both mechanical and electric. i have never had a problem with any of them. i use them as a safety device. as you know with a blown car if something should break at wot in the upper rpm range the reflexes are not fast enough to get off the gas. they rev up too fast. i used the box with the reset and hated it. theres no way to pedal the car. it just shuts the car off. i set my limiters a little tighter on a blown car. i go 500 rpm over what i normally shift. when something lets go by the time the limiter actually does its thing the engine has flashed way past the setting. i have stretched rods because of this. i know it happened because i was running a cable driven tach with a tattle tail. rev limiters are not the most accurate thing. more so with the mechanical. the msd i think is the best electric one out there. for those who want to run elect. this is just my experiences.

 

I wouldn't risk it with anything less than something like a 6al box. I tried to think of a way to shock you at the given RPM but that could be dangerous with DC

 

It depends on if it lights a cylinder with an open intake valve. BOOM!

 

not a detroit piece as detroits run off the rack tower are big and square and are mechanical not electrical

 

even if it would its no big deal. every blower manifold on the street has a spring loaded pressure release valve. on a race engine the burst panel blows. the idea of the blower case or manifold being destroyed are unfounded. its still just a back fire. besides the rev limited is cutting out sparks. its not adding more. it cant fire on the intake if there is no spark.

 

That shifter is cool as hell. Do you have a shot of the under side of it?

You have a good mechanical mind, I know you will figure out the rev limiter deal.

-Abone.