Setting the rev limit
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Joined: Jun 2007
Posts: 94
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From: Salem NH
Setting the rev limit
I have a '69 427/435 tripower with LS 7 heads. I put an MSD 6AL in this spring. Right now I have the MSD 6,000 pill in for the rev limiter.
Does anyone think it would be a benefit to install a 6,300 or 6,500 pill and shift at 6,000 or so?
I don't want to hit the limiter while challenging friends down the strip. How much more power could I expect from the extra 500 or so RPMs?
Thanks
Does anyone think it would be a benefit to install a 6,300 or 6,500 pill and shift at 6,000 or so?
I don't want to hit the limiter while challenging friends down the strip. How much more power could I expect from the extra 500 or so RPMs?
Thanks
Drifting
Joined: Aug 2005
Posts: 1,682
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From: League City TX
Using a rev limiter is typically done to prevent damage during a sudden increase in rpms due to a missed shift or broken component.
When something like that happens, the excessive engine speeds typically only last for a very brief period of time.
For short periods of time your engine is safe at speeds far beyond what it could handle long term, so you can set your chip higher than you might think and still be safe.
I wouldn't hesitate to put even a 7000 rpm chip in it, as long as you pay a little attention to the tach.
When something like that happens, the excessive engine speeds typically only last for a very brief period of time.
For short periods of time your engine is safe at speeds far beyond what it could handle long term, so you can set your chip higher than you might think and still be safe.
I wouldn't hesitate to put even a 7000 rpm chip in it, as long as you pay a little attention to the tach.
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Joined: Apr 1999
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From: Reno Nevada
2024 C3 of the Year Finalist- Modified
First of all it is sad that a company still markets 20+ year old design and even sadder that you bought one. 
When you buy multi spark devices remember two words digital and sequential misfire. The 6AL is neither and can leave you stranded.
Second of all you being the owner driver should know how your motor feels across the rpm band and have an idea of rpm where peak TQ rapidly starts to fall off. But let's say drive it in second gear auto th400 tranny and 3rd gear manual, floor it and by the seat of your pants watching the tach where it drops off. Like it excelerates hard from 3600 - 5600 and then decreases noticably over 6000. you want to set your shift points high enough to put you in the next gear in the fat of your power.
Kind of stated above is that the rev limiter is an engine saver from blowing and should be set just over your max rpm shift points for street cars. Race cars and motorcycles actually use rpm/manual activated shifters that cut the ignition during the shift.
When you buy multi spark devices remember two words digital and sequential misfire. The 6AL is neither and can leave you stranded.
Second of all you being the owner driver should know how your motor feels across the rpm band and have an idea of rpm where peak TQ rapidly starts to fall off. But let's say drive it in second gear auto th400 tranny and 3rd gear manual, floor it and by the seat of your pants watching the tach where it drops off. Like it excelerates hard from 3600 - 5600 and then decreases noticably over 6000. you want to set your shift points high enough to put you in the next gear in the fat of your power.
Kind of stated above is that the rev limiter is an engine saver from blowing and should be set just over your max rpm shift points for street cars. Race cars and motorcycles actually use rpm/manual activated shifters that cut the ignition during the shift.
Le Mans Master
Joined: Sep 2001
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From: Unreconstructed, South Carolina
Every nascar cup, nationwide & truck ... every single one ... has two analog cd boxes ... msd 6 series is the most prevalent ... none are digital. Every single arca late model has a brace of digital mallory cd boxes. Race cars may need cd ignitions but most street cars sure don't. Any cd box can fail; regardless if analog or digital.
you can get a selectable device from msd ... plugs into 6al pill port ... & allows you to twist a **** & select from a range of limits ... say from 6000 thru 8200 in 200 rpm increments ... uses no pills. See msd rpm module selector p/n 8672
you can get a selectable device from msd ... plugs into 6al pill port ... & allows you to twist a **** & select from a range of limits ... say from 6000 thru 8200 in 200 rpm increments ... uses no pills. See msd rpm module selector p/n 8672
Last edited by jackson; May 13, 2010 at 03:20 PM.
Le Mans Master
Joined: Apr 2007
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From: Graceland in a Not Correctly Restored Stingray
System choice aside, unless you'll be hitting it on some straights otherwise, I agree you should set your limiter at ~200 above your highest shift point, whatever you determine that should be.
IMCO, the only time you'd want the limiter right on your shift point would be in a setup such as had by the Reynard in my avatar. Working similar to what gkull described, tho it didn't come outfitted with a full on no-lift shift system, it can be no-lift shifted by appying slight pressure on the sequential lever just as the limiter hits, everything taking place during what would seem a single misfire. OMG, yes, what I wouldn't give to have sequential no-lift in my shark...
IMCO, the only time you'd want the limiter right on your shift point would be in a setup such as had by the Reynard in my avatar. Working similar to what gkull described, tho it didn't come outfitted with a full on no-lift shift system, it can be no-lift shifted by appying slight pressure on the sequential lever just as the limiter hits, everything taking place during what would seem a single misfire. OMG, yes, what I wouldn't give to have sequential no-lift in my shark...
Last edited by TheSkunkWorks; May 13, 2010 at 04:15 PM.
Le Mans Master
Joined: Oct 2006
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From: Gladstone MO
C3 of Year Finalist (appearance mods) 2019
If you're running the factory diaphragm clutch, odds are it'll stick to the floor about 7000. Mine did. That's why it has a scattershield AND a rev limiter set at 7000. Only happened a couple of times to the PO, but it convinced me. And yes, 427/435 then.
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Team Owner
Joined: Apr 1999
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From: Reno Nevada
2024 C3 of the Year Finalist- Modified
Not junky 6AL.............
Also You and I pay for those ingnitions in those cars. NASCAR like anybody is a money deal, they run whatever pays the best. Not because it is the best. I work on race cars every day and travel to races. Why do you think they run twin ignitions? Because that MSD is always crapping out.
When I was drag racing we read every National Dragster paper to see what company was paying what for contingency money. We used every part that paid money and ran the stickers on our dragster. At any NHRA event the contingency money was thousands of dollars where the prize money might have been only $1500 for a first place in CE class racing even at a major event. We were always changing parts even in the motor for the most money
Just look up NHRA contingency money and you will see what i'm talking about. It is a sad reality in racing
Also You and I pay for those ingnitions in those cars. NASCAR like anybody is a money deal, they run whatever pays the best. Not because it is the best. I work on race cars every day and travel to races. Why do you think they run twin ignitions? Because that MSD is always crapping out.
When I was drag racing we read every National Dragster paper to see what company was paying what for contingency money. We used every part that paid money and ran the stickers on our dragster. At any NHRA event the contingency money was thousands of dollars where the prize money might have been only $1500 for a first place in CE class racing even at a major event. We were always changing parts even in the motor for the most money
Just look up NHRA contingency money and you will see what i'm talking about. It is a sad reality in racing
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I'm of the opinion to set the rev limiter high enough to have it only take action IF something really bad happens. I don't want it anywhere near my shift points. I guess I drive by feel more than tach and if I happen to need to wind it a little higher..so be it. I know that doesn't sound right for consistency..but I can usually stay within a few hundreths at the track. For a wannabee Hot Rod street car with a stick trans that's close enough for me.
Actually, I don't use the rev limiter on mine at all. I used to use a shift light...but it just annoyed me. I shift in the 7400-7400 range (usually...sometimes higher).
Anyway...for a well built 427/435 I'd put rev limiter in the 6800-7000 range....again...just to protect it from really bad stuff. If the tires are smoking and you happen to hang in there to 6500 when you usually shift at 6000...I wouldn't worry about it. With those heads....that 427 isn't going to be really coming alive until 5500 anyway.....need to stretch her out a little!
6500 RPM is oval port territory on a 427.
JIM
Actually, I don't use the rev limiter on mine at all. I used to use a shift light...but it just annoyed me. I shift in the 7400-7400 range (usually...sometimes higher).
Anyway...for a well built 427/435 I'd put rev limiter in the 6800-7000 range....again...just to protect it from really bad stuff. If the tires are smoking and you happen to hang in there to 6500 when you usually shift at 6000...I wouldn't worry about it. With those heads....that 427 isn't going to be really coming alive until 5500 anyway.....need to stretch her out a little!
6500 RPM is oval port territory on a 427.
JIM
