making a rev limiter...questions
 

ok so i made a diagram befor i got ahead and try it, but i have a few questions

Attachment 722446

first of all...this this right?

second....do i want to use both coils(leading + trailing) or just leading

and for reference this is the adjustable shift light im planing on using
http://www.summitracing.com/parts/PRO-67005C/?rtype=1

You will need to cut both leading and trailing coils......Are you sure you want to attempt this?

I recommend searching rev limiters on our cars. This is an abrupt cut off....not slowly pulling spark.

i think u may be better off using an ignition system like msd that has the limiter built in.

Cutting off spark on a carburetted car without cutting off fuel at high rpms (wide throttle) will flood your exhaust system with unburned fuel/air mix, which will either ignite on the hot exhaust surfaces as a backfire, or will accumulate in the exhaust system until the next burning wave of exhaust hits it.

Can I watch? I want to see if you get air, or just blow the exhaust out from under the car.

Yeah don't rev limiters drop like every other spark event or something and also
cut fuel which is hard to do with a carbed car. In an EFI world its pretty easy.

I want to watch as well :nod:

It will just put some gas in the exhaust. Makes for nice flames too :)

I have a grounding switch for my MSD which cuts spark.

Interesting... does it cut it completely, or just skip every other ignition cycle?

It grounds it completely. It is a switched ground wire, so when I flick it it will not
send the signal to the coil to spark. Great for pulling the plugs and deflooding, no
more fear of a plug igniting the fuel.

I am sure if you used the adjustable shift light to trigger a relayed ground, it could
be done to stop spark at the RPM.

Wow, sounds like an inexpensive way to drive my neighbors crazier. Hope it works out, I'll def give it a shot after u confirm it working. Goodluck n keep us postd!!!

To be safe, that is why you only cut the leading coil. Trailing is still there to fire off some raw fuel and the leading cut is enough to produce a "soft" limit.

BTW, this is a way better way to rev limit than cutting fuel.

But wait....... Didn't you purchase the Digital 6AL2? It has a limiter built in.....

-billy

na i stoped before i hit the second 'commit to buy'...i realized maping an ignition is awesome but then again i still have a carb'd fuel setup with boost runnign thru it....so really ill just be happy with making a limiter for 50$ and locking the dizzy. plus it will be awesome as hell to turn the limiter to say 3k rpms and then sit in a parking lot and shoot crazy flames lol.... it will also help with launching. i can set it to 7k and hold it there...



but just to be sure before i go and do this, that diagram is correct isnt it???

ya it makes sense to me now if i cut both coils there would be no spark at all which would load up teh exaust with raw gas but if i cut only the leading like bwaits said the trailing would still be there to burn off some of the raw gas and it would be safer.


EDIT: i was just about to order the adjustable shift light but i thought...shift lights are gay looking, they remind me of ricers and hondas so im gonna try to find an adjustable rpm switch that i can mount in the dash :) ill let yall know what i find

what amperage relay should i get?

See, there I'm trapped in "SA-Think" again - - trailing on the SA doesn't constantly fire under all conditions. :blush:

Yep, first change needed for every SA owner. Electric dizzy, toss the ballast resistors and feed a new 12v to the trailing coil.


-billy

I had used a rev limiter on my leading and none on the trailing. It worked awsome and never let the exhaust load up with fuel.

You really feel it when the leading is cut out

I'm running 2- Mallory Hyfire IV boxes, 2- Hyfire Coils, and two soft touch staging rev-limiters. I originally purchased this setup for drag racing w/ NOS. I started with a staging limiter only on the leading. This did not work......at all. The rpm still creeped (in excess of 50-100 rpm/second @ WOT) until I put another limiter on the trailing, and then all was fine.

Now maybe the staging limiters are a bit different than your set up/intentions, but pulling the leading only, I can guess, will still allow ignition creep of a few hundred rpms. So I wouldn't recommend making the limiter at your absolute rpm cap.

I was using them for staging the tree lights, so a few hundred rpm didn't kill me, but if it creeps when you launch it would kill my short times w/ wheel spin.

Yep, that is what I was referring to as a "soft limit". On the track is is great for a shift point. We also used it this way in SCCA rally, it allowed us to "bounce off" the rev limit if you saw the corner was not far off.

As an absolute dead limit you would need to limit both.

-billy

Having an '80, Mazda did that much for me. Just not exceptionally well.

hey nobody has said if that diagram will work... ive been thinking about it again and...wouldnt it make more sense for the rpm signal for the shift light to come off the trailing coil?? if it comes from the leading will i loose signal when the relay closes?

Sorry that I took so long to get back with you. I hope that I got you on the right path. As far as adjustible shift lights, you can pick up a Summit Racing brand for less than 50 bucks. That is what I am using. I have mine tied into the leading and trailing ignition. I am putting down about 400 rwhp and I use my rev limiter to shift from. I usually keep it set at 7k for the street. At 15psi, I can full throttle pull 1rst through 3rd shifting at 7 grand with no problems. The only thing I have to worry about is breaking transmissions :D

I hear to much, but I don't see alot from the "advisees" around here..............

ok i got your pm...looks like that will work great! thanks but i was thinking about something...what if you cut the power on the negative side instead of the posative i think it would be alot safer..

like this: found it on a austrailian rotary forum :) twas a good read
BTW i would be using the green and red configurations

Attachment 722447

I think we safely advised him to do some research to see how others f'd up their engines using rev limiters. I believe using a slow relay to cut ignition will cause the relay to flicker as soon as it comes on. The relay could possibly fail or the ignition could mis-step. Anyone ever looked at a set of stock coils at night with a bad ground? They arc......

I personally would not attempt this. An RPM module is not that expensive and if used with an ignition box can "safely" skip/retard ignition steps to prevent excessive fuel buildup. Think of it like anti-lock brakes. They pulsate to stop excessive lockup. This mod is the equillivant of yanking on the emergency brake.

At that high of an rpm, and to be shooting that much fuel into the combustion chamber just to have it not fire - or be at the mercy of the trailing ignition is a backfire nightmare and is somewhat dangerous. I won't even get into the fact that the fuel will strip the oil from the side housings. Now you're looking at pre-mature heat and wear issues.

If you are going to do it, do it right. If you choose to rig it this way, please post so others see your results. It might work for your needs.

Regardless - good luck and nice job thinking outside the box!

" I believe using a slow relay to cut ignition will cause the relay to flicker as soon as it comes on." <<<<<this is what i thought so i ditched the idea, and started looking around for a tachometer with a rev limiter in it...that uses a transister and is able to switch on and off much faster i think they also use a cappaciter series and a fe other deals...they are very safe and adjustable so i just gotta find one on ebay or something they are kinda hard to come by... actually looking for an old moroso or mallory cuz tha'd be cool but if anyone has a rev limiting tach layign around sell it to me :)

Wow Sorry im so late to reply been buisy with school and havent realy been on the interwebs I have Done this mod just havent gotten the chance to try it out yet seeing as i havent run my car in 2yrs (b00st is worth it) I do Happen to know that it wrks succesfuly on our cars tho here is how i wired mine(Using Leading Coil Only) If you dnt want the ricer looking Shift light look like me do what i did
just tuck it way under the dash were you cant see it Flashing but still be able to adjust your rev limmit.This will aslo be way easier then trying to hunt down a
rev limitting tach and from what i beilive they work the same way.And also heres a link to a vid of a 2nd Gen using the same setup! Hope This Helps.



http://www.youtube.com/watch?v=gKT4U...ext=1&index=18