I recently suggested to the CMC leadership to consider altering the compression rule to simply state a limit of 10.0:1 for iron head cars and 11.0:1 for aluminum head cars. That should give plenty of room for rebuilds on every factory offered combination, and allows some room for bumping up compression on the older (read 302 and 305) cars to assist making 2010 numbers.
Your thoughts appreciated.
Al Fernandez
I personally think this is a bad idea. IIRC the 5.0 had a stock compression ratio of 9.0/1. I think the 305's were in the range of 8.5/1.
This change could promote unnecessary changes to engine internals. It is much easier to bolt on a cheap set of headers to get the power needed.
I would much rather see a compression ratio range. I do not know what the change is in CR due to the clean up of a set of heads but I would think a +/- .25 in CR would be a good range.
Just my thoughts.
-Michael Mosty
CMC #11 Mosty Brothers' Racing
Director - TX Region
Building to a compression ratio in a mod motor that is not available by use of used 96-98 2V pistons, used 99+ 2V pistons or 4V flat tops would force you to buy an $800 set of pistons and rings. Just a point for thought. Parts for these motors aren't cheap!
Micheal has a very good point that you should allow changes to things that can easily be seen in tech with a quick look and not a compression guage or partial tear down.
Ah, fugg it.
The information we have is that with the right parts on a 302 and machine work to lowest allowable specs (as per Ford and typical of multiple rebuilds) you'll end up with ~9.7. My goal of this number is not specifically to prompt people to go out and rebuild for compression, rather to enable them to rebuild using their existing heads and not having to go buy another set. You can go well over 1/4 point with an overbore and fixing of warped heads.
You are right though that an elevated compression ratio is NOT what we'd use as a guide to get 2010 numbers. We'll shoot for getting those using closer to stock compression regardless of how this rule ends up.
Al Fernandez
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Once again, BS.Originally Posted by michaelmosty
260 minus 230 is 30.
30 horsepower.
A set of headers, by themselves, are not gonna give you 30hp on a 305 Chevy.
jb
First-I applaud Al for asking for everyones input.
I am not in favor of this even though its quite likely that it is already happening.
Also, I don't think this proposal is to help people make the numbers for 2010 but to clarify the compression ratio rule-please clarify Al.
MM-says 5.0's came with 9.0/1 so by that theory my LS1 should be allowed 11.8/1. I don't know what the factory compression is on the mod motors, chime in MFW, but isn't it around 9/1? I would assume they have aluminum heads as well which would allow them a possible 2 point increase?
The problem is what Al points out that you can mix/match parts on so many motors to get such an increase in compression. Its my understanding that this has been done for years and has been considered perfectly legal (ala the tony g issue). And in my eyes they are breaking the rules concerning compression ratios. This seems like a way to make their motors legal.
Just seems like the ability to mix/match parts has trumped the compression ratio rule to keep it within factory tolerances. Meaning people don't have to follow the compression ratio rule if they mixed/match legal parts. To me that isn't following all the rules in the rulebook and is illegal. But enough of that-this is about moving forward and clarifying the issue on compression ratios.
Al-I know your goal isn't to have everyone go out and build 10/1 motors but you can bet there will be some who do it. Seems with this type of rules massaging we are headed to the 'do whatever you want to the motor as long as you are under the number'. Where do we end up drawing the line?
I am more in favor of Mitch's suggestion. Or if a certain motor can't make the numbers then maybe it should be done on a motor model basis only. Basically only helping the motors that are underpowered as the LS1's, LT1's, 4.6's don't need any compression help to make the numbers.
Last thing-How could compression ratios be checked at the track? Or at a dyno cert day?
I phrased that wrong, I didn't mean for the headers to give a full 30 hp. Just as I'm sure Al didn't mean for a CR change to get the extra 30 either.Once again, BS.
260 minus 230 is 30.
30 horsepower.
A set of headers, by themselves, are not gonna give you 30hp on a 305 Chevy.
jb
I meant that if you are "close" to the number it would be easier and cheaper to get that final extra from a bolt-on change vs. going deep inside the motor.
-Michael Mosty
CMC #11 Mosty Brothers' Racing
Director - TX Region
two things:
1) like Bryan said, its about clearifing the comp ratio limit. at this point in time we have cars who are following the legal parts update/backdate rule and ending up w/ comp ratios never seen in those applications. this will allow a limit placed thats hard and fast, no gray area. this has nothing to do w/ trying to add power to one platform or another.
as it is now, these numbers posted are not much higher that what has been legally seen already. the other option is to list a comp ratio per engine platform (302, 4.6, LT1, 305, LS1, bla, bla, bla).
2) JB - quit your panicing everytime someone mentions 30hp from headers. no-one involved in helping spec a set-up believes 30hp is gonna get there. they also could have been talking about the small bump a 302 needs to get there a little more easily.
the reality is, a number has to be defined one way or another. we are just looking for input on how it should be worded or limited.
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