l48 rebuild
Le Mans Master
Joined: Mar 2008
Posts: 5,948
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From: Oxford MA-----You just lost the game!!!!
Sorry bout that, yes dynamic of 8.0:1. Thanks Scott.
Your right in that altitude will not have an effect on static CR. Maybe it would be better stated as effective static CR. As altitude increases air density decreases which I'm sure you already know. This has a direct effect on dynamic CR and cylinder pressures. Since most people do not think in the terms of dynamic CR and only static CR the static CR can be raised without exceeding the dynamic CR limit. Therefore given the same cam you could raise the static CR to say 11.0:1 at 5000 ft and still only have a dynamic CR of 8.0:1 due to loss of air density.
Given his engine and a 280 duration cam on a 110 lsa with 64cc heads at sea level his static CR would be 10.03 and dynamic 7.94. Within limits of the iron heads and good power.
Same engine, same cam, but now 56cc heads and above sea level.
At sea level this would give us a 11.04 static CR and an 8.71 dynamic CR. Above the limits we are shooting for.
Move it to 3700 feet and due to loss of air density we now have an effective static CR of 10.3 and a dynamic CR of 7.97. Once again within limits.
I built my engine with this in mind. I live at 4000 feet and operate up to 8000 ft density altitude. By choosing the proper cam I can still develop good power at 8000 ft and not detonate even down to sea level running aluminum heads with pump fuel.
Your right in that altitude will not have an effect on static CR. Maybe it would be better stated as effective static CR. As altitude increases air density decreases which I'm sure you already know. This has a direct effect on dynamic CR and cylinder pressures. Since most people do not think in the terms of dynamic CR and only static CR the static CR can be raised without exceeding the dynamic CR limit. Therefore given the same cam you could raise the static CR to say 11.0:1 at 5000 ft and still only have a dynamic CR of 8.0:1 due to loss of air density.
Given his engine and a 280 duration cam on a 110 lsa with 64cc heads at sea level his static CR would be 10.03 and dynamic 7.94. Within limits of the iron heads and good power.
Same engine, same cam, but now 56cc heads and above sea level.
At sea level this would give us a 11.04 static CR and an 8.71 dynamic CR. Above the limits we are shooting for.
Move it to 3700 feet and due to loss of air density we now have an effective static CR of 10.3 and a dynamic CR of 7.97. Once again within limits.
I built my engine with this in mind. I live at 4000 feet and operate up to 8000 ft density altitude. By choosing the proper cam I can still develop good power at 8000 ft and not detonate even down to sea level running aluminum heads with pump fuel.
Scott
Le Mans Master
Joined: Apr 2011
Posts: 6,284
Likes: 1,171
From: Hermosa
Ah! I thought it might turn out to be something like that, you're a pretty smart guy.
Don't think I'd go that far, but I have my moments....and then there is the rest of the time.Oh, BTW in space your effective SCR would be approximately 0.000000000000001:1. Might take a real short cam to make that work.
BTW, I'd like to thank you once again for all the research you did in measuring the stock dished piston displacement, it really helped me out to get an accurate DCR number when using a DCR calculator.
Last edited by REELAV8R; Oct 30, 2013 at 10:09 PM.
Thread Starter
Pro
Joined: May 2001
Posts: 571
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From: usa
so I have this 454 I could swap in, or trade it for a fresh 30 over short block.
454 thread http://forums.corvetteforum.com/c3-t...-454-id-s.html
454 thread http://forums.corvetteforum.com/c3-t...-454-id-s.html
