Rev limiter for Carb'd cars

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DAlgozine
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Rev limiter for Carb'd cars

Postby DAlgozine » Thu Oct 02, 2014 11:59 am

Any thoughts or input ?

Summary:
Limit Carb car revs, just like all of the EFI cars. Not sure what the max RPM should be, but 6200 is the highest of the EFI engines.
You can easily rev well past 6500 safely, besides how would anyone ever confirm if the internals have been upgraded. And the only benefit to upgraded internals from a performance standpoint would be high revs. Of which only a carb car can take advantage of. Higher revs can be a performance advantage with less shifts and better use and flexibility in various racing conditions. Could be used to a significant advantage for someone interested in pushing the boundaries. No limit on anything within the CMC rules, doesn’t match the rule set.
A simple chip in the ignition box is fair and simple to police.
There are a couple different versions of these
http://www.jegs.com/i/MSD-Ignition/121/ ... oreDetails
Would this be a simple , inexpensive ( $ 125 ) method?

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---4) Reasoning for change MUST include at least 1 of the following:
---------->a) Will decrease series cost because… Possibly less engine wear / breakage with a rev limit

---------->b) Will increase driver safety because… None


---------->c) Will promote series growth because... Better level the playing field. Being able to rev to 6500 to 7000 is an advantage. Less shifts for certain locations on at some tracks. Wider range of RPM’s allows more flexibility in certain driving situations . Will make it equal to EFI cars

---------->d) Will improve competition because… Same as above

---------->e) Will provide more clarity because… Carb revs are currently open , which in a restrictive class, doesn’t match the rest of the rule set
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Postby D. Francis » Fri Oct 03, 2014 8:43 am

I thought rev limiters were already allowed as rev limiters - I always wanted to wire up one clutch in/first gear selected as launch control.
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Re: Rev limiter for Carb'd cars

Postby adam_ginsberg » Fri Oct 03, 2014 3:21 pm

DAlgozine wrote:Any thoughts or input ?


Seriously?? When was the last time you read the rules?

2014 CMC Rules, Section 7.23 Ignition wrote:7.23.2 Any rev limiting device may be used provided that is its only function.


It's been there since 2007.

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Re: Rev limiter for Carb'd cars

Postby DAlgozine » Fri Oct 03, 2014 3:37 pm

adam_ginsberg wrote:
DAlgozine wrote:Any thoughts or input ?


Seriously?? When was the last time you read the rules?

2014 CMC Rules, Section 7.23 Ignition wrote:7.23.2 Any rev limiting device may be used provided that is its only function.


It's been there since 2007.


LOL
Where's the love
Read my post again! Perhaps it's not clear
The questions is " should carbs cars have a maximum rev limit" ? Currently they do not have a max, like all of the EFI cars do
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Postby Glenn » Fri Oct 03, 2014 5:02 pm

Dave A - I understood your point from the get go. I pointed this out a few years back. I am in favor.

More detailed post to come. Hate typing on my phone.
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Postby Glenn » Fri Oct 03, 2014 6:27 pm

By not having a rev limiter in place, there is a chance to extend the RPM's in places allowing you to not have to shift up between corners when those w/ limiters have to. I have myself rode the limiter in places as it was faster than shifting up one and right back down one. So while the motors power may be dropping off, there is an advantage to perform less shifts per lap. For every saved upshift, there is a saved down shift (yes I know there are times when we drop down more than 2 gears at a time - but you get my point).

When the motors were at the 230hp limit this was a concern, but quickly dismissed as the motors made no power in the RPM's where we were concerned. Advantage/disadvantage was quickly dismissed as a wash. Now that we have some motors w/ non-OEM cams, this can be problem.

I know we don't want to remove all RPM limits as that will make folks want to spend money on non-legal internals.

I would love to see this debated from both sides.


Adam - ........ never mind.
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Postby TX#11CMC » Sat Oct 04, 2014 11:08 am

I think this is a great rule.
There is no reason IMO to not have a limiter on the carb cars with the exception that it is more $$ to spend.
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Postby MHISSTC » Sat Oct 04, 2014 5:22 pm

Is 6k the consensus on a reasonable redline for any of the carbed engines?
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Postby Glenn » Sat Oct 04, 2014 5:24 pm

Any reason to not make it the same as efi cars?
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Postby MHISSTC » Sat Oct 04, 2014 7:17 pm

Glenn wrote:Any reason to not make it the same as efi cars?


I'm not sure.

Are the GM and Ford EFI redlines the same right now?

I think the spec carb engine should be allowed to go a little bit higher than the 6200 RPM redline as given previously in the EFI setup example.

I asked about what is a reasonable redline because I'm interested in knowing what the actual structural limitations are of the stock internals and hardware more so than merely transposing the limitations from an engine that is equipped with a much different air and fuel delivery system. I haven't researched the structural engineering aspect of the engines as much as I've done the math every which way with all of the different rules of thumbs regarding carb, cam, header and intake sizing, etc. Going through that exercise, it seems to me the components specifically allowed on the spec carb engines are sized on the large end of the scale, or are even slightly over-large, for the RPM and power range we're shooting for with these engines. For those components to operate properly and most efficiently, it seems to me that the max RPM allowed on the spec carbed engine may have to be a bit higher than those with an EFI setup. Something like 6500 RPM (if not higher) seems like a completely reasonable value for that setup of components. However, I want to know if it's even reasonable to think a set of stock cast pistons, crank, and connecting rods are up still up to the task using the hardware found in a basic rebuild kit. Is the additional strength garnered from using ARP hardware throughout the engine is beneficial? Or, is ARP hardware overkill if the rotating assembly isn't even up to the task?
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Postby Supercharged111 » Sat Oct 04, 2014 8:29 pm

Those alphabet cams peak before 6,000, I myself was thinking 6,250 like EFI. . . but then again the carb'd Fords don't make the torque numbers so we throw them a bone? Then there's the Chevies. 212/222 on a 112 for the spec engine. That's more duration and less lift than an LT1 cam. Perhaps we take a peek at what carb'd guys' dyno pulls look like? We can speculate where peak power is, but not so much how quickly it falls off. Maybe we base it off of where the EFI cars' rev limit is relative to their respective peak power and sort of extrapolate to the carbs?
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Postby BADVENM » Sat Oct 04, 2014 8:46 pm

Is there a way to see/compare dyno charts from an EFI Ford 302 vs a carbed 302 in our series to see if there is any advantage for either setup? Compare hp/tq for various rpm levels? I guess the same would hold true comparing similar GM setups.

After I read this I think my question is similar to Supercharged111's.
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Postby Supercharged111 » Sun Oct 05, 2014 8:20 am

So, for example, I've lost 9.5% of peak power at 5,700 RPM compared to my peak around 5,200 RPM. Now my dynos suck, so we should definitely use a healthier car to base it off of, but this is kind of what I'm getting at with the carbs. If everyone (EFI) is losing around 10% of their peak power at their rev limit, then we just get a concensus of where the carb guys are peaking and have their rev cut be where most lose XX% of peak power.

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Postby PeteL » Mon Oct 06, 2014 8:28 am

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?

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Postby Glenn » Mon Oct 06, 2014 8:33 am

If there is an issue w/ power under the curve for carbs vs EFI motors, lets address that in a different thread. That is a different problem that was is addressed here w/ the original post.

The reason for the original post was to close a possible advantage created by carb cars not having a hard RPM limit vs the EFI cars having one. Regardless of power and where it is made in the RPM, 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.
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