Bernardd Posted July 14, 2006 Share Posted July 14, 2006 I have a custom elgin cam. I did a compression test and came out with 105 across all the cylinders. Last year with a stock cam I had 130's with different values across the cylinders. The engine pulls 14in of vac at idle where last year it pulled 18 or so. I bought the head/cam combo used and the previous owner says the vacuum on his engine was very similar. Thoughts??? Bernard Quote Link to comment Share on other sites More sharing options...
naviathan Posted July 14, 2006 Share Posted July 14, 2006 It's a result of valve overlap. The bigger the cam the greater the length of time for valve overlap as it goes between the exhaust and intake stroke. Quote Link to comment Share on other sites More sharing options...
spacecoastz Posted July 14, 2006 Share Posted July 14, 2006 Hey Bernardd, long time bro! Check this out. http://www.datsport.com/Racer_Brown_Menu.html Excellent info on cams and the L motor. Quote Link to comment Share on other sites More sharing options...
Twoeightnine Posted July 14, 2006 Share Posted July 14, 2006 Isn't a performance cams job to get more fuel and air into the cylinder? That being the case, more fuel and air into the original cylinder would mean that at top dead center we have compressed more volume into the same space resulting in greater compression readings. Right? Quote Link to comment Share on other sites More sharing options...
naviathan Posted July 14, 2006 Share Posted July 14, 2006 No it's a common misconception, you lose compression during the valve overlap which loses some of that extra air/fuel charge it's pulling in. Really you just flow better so it's easier for the cylinder to pull that air/fuel in, not pull in more. Less power lost in pulling it in brings more power by lack of strain. Quote Link to comment Share on other sites More sharing options...
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