Rev limiter for Carb'd cars

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Glenn
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Postby Glenn » Mon Oct 06, 2014 8:35 am

PeteL wrote:I think we're getting a little ahead of ourselves discussing what the rev limit should be.

Every engine chassis combination has advantages and disadvantages. LT1's have aluminum heads but make their torque way down low, LS1s are all aluminum and have an anvil flat torque curve but have to run 50 lbs heavier which they can put low, right and aft, the Fords have their issues making power but have a lower min weight. So carb cars have one performance advantage, an RPM limit set mechanically as opposed to electronically.

Is there any evidence that carb cars are running amok and need to be reined in? Have the carbed cars been dominating at the regional or national level? The real question we need to get at is not whether a lack of an imposed rev limit is an advantage but is it an advantage that is not already counterbalanced by an disadvantage. Is there a real competitive advantage factoring everything in?

First step in solving a problem, make sure there is really a problem.


Great post. Spot on.
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Postby DAlgozine » Mon Oct 06, 2014 9:04 am

I don't know what the limit should be, and I don't think it should be anything that inhibits the performance of the current "standard / typical" carb'd car, however there should be a maximum limit to RPM's.
My semi educated guess is more then 6200, but less than 6500.

My point is not so much about solving a current problem, but more about imposing a sensible limit.
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Postby MHISSTC » Mon Oct 06, 2014 1:51 pm

Glenn wrote:...I would love to have a couple hundred RPM's to use in a couple spots at my event in a few days to remove the need to short shift mid straight so I don't have to do it at the end and then right back down again .5 to 1 second later.


And I love to have the low end torque and table top flat curve enjoyed by the GM engines so I'm not forced to downshift to a lower gear to keep the engine in the power band exiting corners only to have to up-shift later. It sounds like we're equally handicapped at opposite ends of the RPM range.

I like Pete L's post. Is there really a problem here that needs to be solved? I haven't seen any carbed cars dominating the series and I don't know of anybody who's cheating the series by blueprinting their engines and using forged I-beam rods in order to rev it to 8k.
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Postby Glenn » Mon Oct 06, 2014 1:59 pm

Scott - show me at what rpm the LT1 has an advantage with regards to TQ.
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Postby Supercharged111 » Mon Oct 06, 2014 2:02 pm

MHISSTC wrote:
Glenn wrote:...I would love to have a couple hundred RPM's to use in a couple spots at my event in a few days to remove the need to short shift mid straight so I don't have to do it at the end and then right back down again .5 to 1 second later.


And I love to have the low end torque and table top flat curve enjoyed by the GM engines so I'm not forced to downshift to a lower gear to keep the engine in the power band exiting corners only to have to up-shift later. It sounds like we're equally handicapped at opposite ends of the RPM range.

I like Pete L's post. Is there really a problem here that needs to be solved? I haven't seen any carbed cars dominating the series and I don't know of anybody who's cheating the series by blueprinting their engines and using forged I-beam rods in order to rev it to 8k.


Don't forget there is such a thing as a carb'd Chevy 350 and that the Fords can run lighter. These cars have many, many differences so they're not exactly apples and oranges. Even with a table top torque curve it's still advantageous to wind an LT1 right to the limit.
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Glenn
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Postby Glenn » Mon Oct 06, 2014 2:06 pm

No carbs for the 4th gens. Not allowed.
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Postby Supercharged111 » Mon Oct 06, 2014 2:07 pm

Glenn wrote:No carbs for the 4th gens. Not allowed.


I never said 4th gen. But I can see where it may have been inferred. To be clear I was referring to 3rd gen F-bodies.
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Postby BryanL » Mon Oct 06, 2014 2:21 pm

PeteL wrote:I think we're getting a little ahead of ourselves discussing what the rev limit should be.

Every engine chassis combination has advantages and disadvantages. LT1's have aluminum heads but make their torque way down low, LS1s are all aluminum and have an anvil flat torque curve but have to run 50 lbs heavier which they can put low, right and aft, the Fords have their issues making power but have a lower min weight. So carb cars have one performance advantage, an RPM limit set mechanically as opposed to electronically.

Is there any evidence that carb cars are running amok and need to be reined in? Have the carbed cars been dominating at the regional or national level? The real question we need to get at is not whether a lack of an imposed rev limit is an advantage but is it an advantage that is not already counterbalanced by an disadvantage. Is there a real competitive advantage factoring everything in?

First step in solving a problem, make sure there is really a problem.

So as it stands a Fox can run EFI with a rev limit or a carb without it. The same exact platform so doesn't have anything to do with other chassis parity.
The question is with the bigger cams, big intakes, big carbs should the carbed cars be limited on their RPM? Obviously looking at some dynos of those cars would be helpful.
Doesn't really matter if they aren't running amok in CMC. IF they are able to run midpack but with an advantage over another midpack guy or a backmarker then that is a problem.
I only know of two Fox's running carbs in Texas and I believe both of them have to restrict their cars power.

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Postby DAlgozine » Mon Oct 06, 2014 2:22 pm

MHISSTC wrote: I don't know of anybody who's cheating the series by blueprinting their engines and using forged I-beam rods in order to rev it to 8k.


How would anyone know if someone hasn't spent some big money on internals and is currently spinning it up to 8k? Haven't seen an engine tear down yet, and I hope I never do. This eliminates the need for a tear down, because with a rev limit , there is nearly zero performance advantage to big dollar internals.
Doesn't mean someone isn't doing it now or someone will do it in near future.

There are a couple carb'd racers that have used this as an advantage. I've raced with them, and I even rented one the cars a few years ago

This isn't a major item, but if there are limits on nearly every other component, engine, trans, rear end, shocks, wheels , "Rear diff covers" (had to figure out a way to work that into a post this year) etc....., why not on a carb'd engine.
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Postby MHISSTC » Mon Oct 06, 2014 9:33 pm

DAlgozine wrote:..."Rear diff covers" (had to figure out a way to work that into a post this year)...


:lol:

Although we had several in mind, we purposefully did not submit any RCRs this year..
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Postby nape » Tue Oct 07, 2014 11:41 am

I've been biting my tongue on this since I've yet to get the car together, but I really agree with Pete's post.

Every chassis has a handicap in one way or another. Has anyone even looked at dyno sheets to see if this is a possible red herring before we go Dianne Feinstein on this?

I can understand that it may be frustrating for someone to be able to hold a gear longer, but what's next? Spec final drive ratio? It's sure frustrating when someone else chooses the right ratio and they don't have to shift and you do. Same theory.
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Postby wastntim » Tue Oct 07, 2014 1:34 pm

nape wrote:I can understand that it may be frustrating for someone to be able to hold a gear longer, but what's next? Spec final drive ratio? It's sure frustrating when someone else chooses the right ratio and they don't have to shift and you do. Same theory.


I think the key phrase is "chooses the right ratio". The choice in this matter is whether you choose to run carb'd or fuel injection as their is no choice as to your rev limiter when running fuel injection as we are limited to the oem program on the PCM.

When Bob was still running his carb'd motor, he would pass me on the straights everytime I had to shift at 5,700 rpm and he could wind his motor out to 6,500rpm. He passed me at RA this way.

The question simply comes down to whether or not the directors want to have certain platforms have advantages over the others IN CERTAIN AREAS?

To be honest, I think all of the cars should have the same restriction on rpm and it should be set. This would require FI cars to program their PCMs to be the same, but it would eliminate this disparity. This would also eliminate the disparity that can exist on the PCMs. Although I am not an expert, I believe that depending on the year the car was built, the PCM may have different rev limiters programmed in it already. This results in "PCM shopping" whereby individuals will buy certain year PCMs as they have a higher rev limiter.

Additionally, limiting the revs easy enough to check on the dyno.
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Postby Supercharged111 » Tue Oct 07, 2014 1:53 pm

We can't have one limiter to rule them all, that would only work if everyone had the same engine. AFAIK autos and manuals are the only ones that have differing limiters and the rest are all the same regardless of year. Doesn't a Fox body have a limiter if running the factory distributor with brain box? Someone school me on that one, because I could swear that they do.
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Glenn
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Postby Glenn » Tue Oct 07, 2014 2:01 pm

If a 3rd gen with a carb can spin 6500, that is reason enough to limit them. If we told everyone today that all limiters can be set to 6500, who here wouldn't make that change? That alone is reason enough to impose a limit. But who says 6500 is the real number? What if today it is 6500 and tomorrow it is 6800? May as well set a limit now so guys dont start dropping coin on crazy springs and valves.
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Postby suck fumes » Tue Oct 07, 2014 2:37 pm

Even if you spin it up that high almost all cars stop making power at 5800-6000 sometimes less so there is not really a big adv there I don't think.
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