IQ52
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Hah! Darn funny and true. Thanks!
440 500 build
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BSB67
Well-Known Member
Technically, it's only the ICL that matters, not LSA. Arguable they usually go hand in hand (LSA & ICL) with the ever popular "4° advanced ground in", but not always.
An intake lobe installed at 110° CL will have the same intake closing point and dynamic compression ratio no matter what the LSA is, no matter what the overlap is.
Hemirunner
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As a collective, we get way too caught up in the irrelevant specs of a camshaft. I was once told to get the IO, IC, EO and EC points correct and the rest is just math...
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Don't forget the EI,EI,OH...
Lol.
BSB67
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I don't know if I would call them irrelevant. But certainly to the smart cam people, those are the 4 events that really matter, and the rest come along for the ride. I will say that we spend a lot of time bantering about on cam specs that 95% of the time don't really matter.
When I was young, I would change cams on Saturday mornings. Today, we'll spend two weeks talking about cam specs.
Hemirunner
Well-Known Member
I’ve got 3 cams for 3 different turbo combos spec’d by 3 different turbo cam experts. One is SBF, one BBC, one BBM. All 3 have similar HP targets, similar CR and head flow and similar intended uses. All 3 IC points are within a 3 degree spread. Things that make you go hmmm....
66Satellite47
Well-Known Member
I give up.
ChargerST
Well-Known Member
Some good points here! Can you gives us some more insight on the quench issue with larger bore engines (BBM)? I would assume that large bore engines need more quench distance as the quench area may become too large resulting in trapped charge? Maybe even slightly angle the quench pad towards the center of the combustion chamber to force the charge in the center? I'm just speculating here.
If you need to run dish pistons for compression ratio reasons would you rather run a spherical dish or kidney/combustion chamber shaped dish piston?
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Heimedw
Well-Known Member
I believe in theory the closer the quench the less likely you will have detonation. I would love to hear the science behind that because I still have a hard time rapping my head around that one.
'68 Coronet R/T
Well-Known Member
From: https://www.hotrod.com/articles/ccrp-9812-secrets-of-camshaft-power/
Overlap
Duration, lift, and LDA combine to produce an “overlap triangle.” The greater the duration and lift the more overlap area, LDAs remaining equal. Given the same duration, LDA and overlap are inversely proportional: Increased LDA decreases overlap (and vice versa). More overlap decreases low-rpm vacuum and response, but in the midrange overlap improves the signal provided by the fast-moving exhaust to the incoming intake charge. This increased signal typically provides a noticeable engine acceleration improvement.
Less overlap increases efficiency by reducing the amount of raw fuel that escapes through the exhaust, while improving low-end response due to less reversion of the exhaust gases back up the intake port; the result is better idle, a stronger vacuum signal, and improved fuel economy.
Due to the differences in cylinder head, intake, and exhaust configuration, different engine combos are extremely sensitive to the camshaft’s overlap region. Not only is the duration and area of the overlap triangle important but also its overall shape. Much recent progress in cam design has been due to careful tailoring of the shape of the overlap triangle. According to Comp, the most critical engine factors for optimizing overlap include intake system efficiency, exhaust system efficiency, and how well the heads flow from the intake toward the exhaust with both valves slightly open.
Overlap
Duration, lift, and LDA combine to produce an “overlap triangle.” The greater the duration and lift the more overlap area, LDAs remaining equal. Given the same duration, LDA and overlap are inversely proportional: Increased LDA decreases overlap (and vice versa). More overlap decreases low-rpm vacuum and response, but in the midrange overlap improves the signal provided by the fast-moving exhaust to the incoming intake charge. This increased signal typically provides a noticeable engine acceleration improvement.
Less overlap increases efficiency by reducing the amount of raw fuel that escapes through the exhaust, while improving low-end response due to less reversion of the exhaust gases back up the intake port; the result is better idle, a stronger vacuum signal, and improved fuel economy.
Due to the differences in cylinder head, intake, and exhaust configuration, different engine combos are extremely sensitive to the camshaft’s overlap region. Not only is the duration and area of the overlap triangle important but also its overall shape. Much recent progress in cam design has been due to careful tailoring of the shape of the overlap triangle. According to Comp, the most critical engine factors for optimizing overlap include intake system efficiency, exhaust system efficiency, and how well the heads flow from the intake toward the exhaust with both valves slightly open.
moper
Well-Known Member
[QUOTE="IQ52, post: 911119635, member: 7725"
Cams with more overlap don't reduce cranking compression because of the overlap. It's because they generally have longer intake duration and close the intake valve later in the compression stroke.
[/QUOTE]
The only event that makes any difference is as IQ has said: the intake valve closing event. As he says here, people always relate the overlap with the pressure changes, when all more overlap "might" represent is a different intake closing point. But that's a might. It's all up to the cam's designer and you won't find much info on that aside from intake closure point at .006" or .050" for shelf cams, which themselves can be misleading.
One should not assume one can "fix" too much static compression with a "larger" camshaft. Ultimately what ends up happening in those cases is the cylinder pressures rise as rpm does, and the engine experiences detonation or loss of controlled combustion anyway. Its always better to err to the lower side. ALWAYS.
Cams with more overlap don't reduce cranking compression because of the overlap. It's because they generally have longer intake duration and close the intake valve later in the compression stroke.
[/QUOTE]
The only event that makes any difference is as IQ has said: the intake valve closing event. As he says here, people always relate the overlap with the pressure changes, when all more overlap "might" represent is a different intake closing point. But that's a might. It's all up to the cam's designer and you won't find much info on that aside from intake closure point at .006" or .050" for shelf cams, which themselves can be misleading.
One should not assume one can "fix" too much static compression with a "larger" camshaft. Ultimately what ends up happening in those cases is the cylinder pressures rise as rpm does, and the engine experiences detonation or loss of controlled combustion anyway. Its always better to err to the lower side. ALWAYS.
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There are a number of stellar contributors on this forum for detailed engine build information, and Jim (IQ52) is my go to for the final word, even though he and I had a back and forth about valve springs until we wound up on the same page.
68 HEMI GTS
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The poor OP just wanted some advice on a pump gas street engine. I think this may have went a bit off track.. 
1967coronet440
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As per usual lolThe poor OP just wanted some advice on a pump gas street engine. I think this may have went a bit off track..
PRHeads
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My guess is, something along the lines of......”why are you listening to those clowns on the internet anyway”?
PRHeads
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The poor OP just wanted some advice on a pump gas street engine. I think this may have went a bit off track..
He got some bonus info!!!
'68 Coronet R/T
Well-Known Member
I don't think Stubby has responded since his initial post. Hope we didn't scare him off.
1967coronet440
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The Info provided is great, it can be overwhelming for your average enthusiast but all factors should be considered in an investment like a stroker build IMO.
That being said you need to do your research on your builder also, if you don’t trust him what’s the point. If you Go back to him and tell him oh well this guy on the internet says do it this way. Let me know how that works out for you.
That being said you need to do your research on your builder also, if you don’t trust him what’s the point. If you Go back to him and tell him oh well this guy on the internet says do it this way. Let me know how that works out for you.
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