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Author Topic:   Rev Limiter
WesternAuto17
Dirt Forum Champ
Total posts: 569
posted June 01, 2005 06:13 AM  
How bad of an idea is this?

I want to make sure my new motor does not get over 6800 rpm. MSD has a digital rpm activated switched that can be set to normally closed until a specified rmp.

What if I were to wire my distributor up to a relay which is operated by the rpm switch. When I hit 6800, the switch (and consequently, the relay) opens and shuts down the distributor. As soon as the the motor shuts off, rpms go to 0 and the rpm switch closes again. At this point, power is restored to the distributor, and the motor will retart because the rear wheels will keep to engine spinning. I think all this would happen in a couple tenths of a second.

It seems to me that this would not be good for the motor, but maybe it would be better than over revving. Maybe just wiring the switch up to a light is a better solution.

FYI - a 6AL MSD isn't an option.

TEAMPCR
Dirt Freak

Total posts: 238
posted June 01, 2005 06:52 AM  
Engine is likely to backfire on restart.

leapinlizard
Dirt Freak

Total posts: 402
posted June 01, 2005 07:45 AM  
Waiting for an engine to coast down from 6800 RPM will take at least a second to a second and a half depending on moment of inertia.

NJantz
Dirt Forum Champ
Total posts: 755
posted June 01, 2005 08:32 AM  
Why not just buy a soft touch rev controller from MSD? They work by dropping fire to the cylinder on a random basis.

[This message has been edited by NJantz (edited June 01, 2005).]

dirtbuster
Dirt Forum Champ
Total posts: 2007
posted June 01, 2005 09:08 AM  
It would prob be kind of hard on things since it would most likely backfire as it restarted. Thats why the MSD rev controls alternatlely drop cylinders instead of shutting the whole thing down.

WesternAuto17
Dirt Forum Champ
Total posts: 569
posted June 01, 2005 09:41 AM  
That's pretty much what I thought.

I didn't realize I could get the Soft Touch outside of an MSD box. I'll look into that, thanks...

[This message has been edited by WesternAuto17 (edited June 01, 2005).]

Eljojo
Dirt Forum Champ
Total posts: 968
posted June 01, 2005 01:27 PM  
I dunno, but my thinking is this: Motor starts revving, goes from 6799 to 6800 and looses fire IMMEDIATELY quits revving and goes to 6799 and climbing...dut ta dut ta dut ta dut.......am I out to lunch?

WesternAuto17
Dirt Forum Champ
Total posts: 569
posted June 01, 2005 01:47 PM  
Alright, alright already.

I admitted it was a bad idea, I just didn't know how bad. Well, consensus is that it would be a very bad idea.

TEAMPCR
Dirt Freak

Total posts: 238
posted June 01, 2005 03:31 PM  
Shoot, just run 'er up to 8-grand and see what happens. It'll be O.K.

WesternAuto17
Dirt Forum Champ
Total posts: 569
posted June 02, 2005 05:12 AM  
I'll tell you what will happen - KA-BOOM, followed by a serious case of lumpy oil pan.

dirtTurd
Dirt Maniac

Total posts: 115
posted June 02, 2005 05:51 AM  
NJantz,
Will it work on 6-t, if so how come alot of people switch to 6-al.

thanks

NJantz
Dirt Forum Champ
Total posts: 755
posted June 02, 2005 08:01 AM  
Yes MSD makes a rev control for the 6T.
PN 8738.

dirtTurd
Dirt Maniac

Total posts: 115
posted June 02, 2005 08:02 AM  
THANK YOU

WesternAuto17
Dirt Forum Champ
Total posts: 569
posted June 02, 2005 08:07 AM  
So how does the Soft Touch limiter wire into an HEI?

rrrrick
Dirt Maniac

Total posts: 192
posted June 02, 2005 02:37 PM  
Hey now.. it is probably really really bad for the engine.... but just think of how the fans will get a kick out of the big back fire your car will do

trasrat89
Dirt Full Roller

Total posts: 46
posted June 03, 2005 05:14 AM  
Heck, back in my high school days, we used to make our cars backfire on purpose to see who could get the loudest bang. We'd shut off the ignition, coast awhile, then turn the key back on. BANG!!! It was fun till the day I had the ol mans 68 ford station wagon out while I was supposed to be in school, & blew the muffler clean off the thing. BUSTED!! Good times, goood times. LMAO!!

mansfief
Dirt Maniac

Total posts: 128
posted June 03, 2005 09:25 AM  
Transrat, sounds like you grew up with my brother. He did that with a 52 Chevy. Them old babbit rods diden't like it either. The worst he ever did was take our 49 Chevey truck, take a vacuum line and put it in a gallon of oil , and back up to a business and leave it run. Wow, If the owner could have seen us, he would have shot us. Those was the days.

streetstock82
Dirt Forum Racer

Total posts: 81
posted June 12, 2005 05:28 PM  
you can buy those soft touch pin controllers for around 50 bucks. I run d.u.i ignition on my modified and no msd box and the soft touch works fine. its easy to hook up.

WesternAuto17
Dirt Forum Champ
Total posts: 569
posted June 13, 2005 06:49 AM  
Thanks, I have since bought a Soft Touch and will install it this week.

Thanks for the input guys.

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