boardkid280z Posted April 8, 2009 Share Posted April 8, 2009 Longer duration will lower cylinder pressure? Won't that let more air in the piston, causing the density of the air to be higher when it's compressed, causing higher cylinder pressure? Quote Link to comment Share on other sites More sharing options...
Pyro Posted April 8, 2009 Share Posted April 8, 2009 no, compression doesn't begin until the intake valve closes. until then, air is pushed back into the intake. yes, boost helps fill the cylinder, but doesn't make nearly the cylinder pressure the piston does when compressing the charge. Quote Link to comment Share on other sites More sharing options...
Brad-ManQ45 Posted April 9, 2009 Share Posted April 9, 2009 yes, boost helps fill the cylinder, but doesn't make nearly the cylinder pressure the piston does when compressing the charge. I don't think anyone running more than 15 PSI boost (or anything more than their stock compression ratio in boost) will agree with you... Air volume is more than doubled at that amount of boost. Quote Link to comment Share on other sites More sharing options...
bradyzq Posted April 9, 2009 Share Posted April 9, 2009 I don't think anyone running more than 15 PSI boost (or anything more than their stock compression ratio in boost) will agree with you... Air volume is more than doubled at that amount of boost. Right, but compressing the charge will multiply the pressure by 8 or so. Quote Link to comment Share on other sites More sharing options...
Pyro Posted April 9, 2009 Share Posted April 9, 2009 of course adding boost increases cylinder pressure. that is a given. but, delaying the intake valve closing point with a longer duration cam will lower cylinder pressure, with or without boost. yes that is right, the pressure from the pistons makes an order of magnitude (10x) more pressure than the boost from the turbo. Quote Link to comment Share on other sites More sharing options...
Careless Posted April 10, 2009 Share Posted April 10, 2009 yes that is right, the pressure from the pistons makes an order of magnitude (10x) more pressure than the boost from the turbo. it sure as hell better! or my 150psi I got on my compression testing gauge is telling me my engine is a 150:1 compression ratio. LOL where's that 1000 octane gas? Quote Link to comment Share on other sites More sharing options...
boardkid280z Posted April 11, 2009 Share Posted April 11, 2009 it sure as hell better! or my 150psi I got on my compression testing gauge is telling me my engine is a 150:1 compression ratio. LOL where's that 1000 octane gas? Well the 150psi is the number on the left of the ratio, and the number on the right is atmospheric (approximately). Which is 14.7psi, not 1 psi. So the ratio of compression for your motor is 150psi:14.7psi or 10.2:1 approximately. Quote Link to comment Share on other sites More sharing options...
Careless Posted April 12, 2009 Share Posted April 12, 2009 not going to dispute that, as it is a ratio, and not a measure of anything unless stated (as you did)... but I think you missed my joke. Quote Link to comment Share on other sites More sharing options...
boardkid280z Posted April 13, 2009 Share Posted April 13, 2009 but I think you missed my joke. Lol, yep, sorry - my brain hasn't been working well this past weekend. Quote Link to comment Share on other sites More sharing options...
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