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Quick question on advancing/retarding cam

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Old Jan 21, 2014 | 08:30 AM
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Default Quick question on advancing/retarding cam

I know that properly degreeing the cam (as apposed to just installing it dot to dot) will provide the best performance for the given application. Just not sure how that applies to the ground in advance/retard the cam already has.

Say you have a 112 LSA cam with +2* of advance ground in (thus 110 ICL). If for example you retard that cam 1*, what changes as far as the engine sees?

Will it be a 112+1 (111 ICL) or since the 2* of advance are ground in permanently, it will always be a +2 so in this example retarding the cam 1* will turn it into a 113+2 (111 ICL)?
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Old Jan 21, 2014 | 12:31 PM
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The latest Hot Rod mag March 2014 (not sure) had a really good article on advancing/retarding the cam for the best overall performance with a compression gauge. Regardless of what was advertized on the cam or what you think may be right. They set up No. one cylinder with rockers, valves, etc and cranked the motor (using the starter) and measured the compression. They then retarded the cam 2 degrees and repeated the test. Then advance the cam 2 degrees and repeated. Which ever way they went they kept going (advance or retarding) until they got the most compression. If I find the article I will reply back.
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Old Jan 21, 2014 | 01:31 PM
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Originally Posted by redtan
I know that properly degreeing the cam (as apposed to just installing it dot to dot) will provide the best performance for the given application. Just not sure how that applies to the ground in advance/retard the cam already has.

Say you have a 112 LSA cam with +2* of advance ground in (thus 110 ICL). If for example you retard that cam 1*, what changes as far as the engine sees?

Will it be a 112+1 (111 ICL) or since the 2* of advance are ground in permanently, it will always be a +2 so in this example retarding the cam 1* will turn it into a 113+2 (111 ICL)?
LSA never changes. If it is a 112 LSA with 2 degrees of advance ground in, it has a 110ICL and a 114 ECL (intake/exhaust centerline). If you manually advance it another degree, it will have a 109icl and a 115 ECL (they move opposite directions). The engine doesn't know the difference between a cam with advance ground in, and one that is manually added via the timing set. The biggest purpose behind degreeing a cam is to ensure the ICL (advance) is ground in and/or set where you want it to be, since you can't change lsa.
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Old Jan 21, 2014 | 05:43 PM
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Just following up... Diet is correct. Additionally maximizing cylinder pressure or dynamic compression; the technique that Hot Rod mag March 2014 talked about; optimizes camshaft position for any engine combination.
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Old Jan 21, 2014 | 07:27 PM
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So in my example, if I had a 112+2 with a 110 ICL cam and retarded it 2*, it would turn into a 112+0 with a 112 ICL
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Old Jan 21, 2014 | 07:41 PM
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yes, though most ls engines like 3-5 degrees of advance
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