Thread: Effective compression pressure ratio ?

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I am confused about selecting the proper compression ratio for my 498 build. I hear a lot of people say do not run over 9.1 with cast iron heads or 10.1 with aluminum on pump fuel. Are they talking static or effective compression ratios? After playing around with the calculator on the KB web site it seams to me depending on cam selection that you can run a much higher than 9.1 static compression engine on pump fuel, or is my thinking way out of the park. If so are these calculators accurate for real world applications. Any comments on this subject would be of great help.

they are talking about static. I'd at least run 9.5 to 1.

Thanks for the info mrbigg. What do suggest for rod length on a 496, 6.135 or 6.385" I have heard pro's and cons on both?

i built them with both size rods if your going internal bal then go with the 6.385 rod you will have more counter weight on the crank if .low $ then i use the hpers speed pros pistons and stock rod 6.135 and ex bal .any time you can put a longer rod in it helps some what you get deep in to the oil rail then you will have to run oil ring spacers for street use i would use the 6.135 rod for race builds i move up to the 6.385 rods here a long rod