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: 396 eng Jim W Nov 19th, 02, 2:50 PM I just finished my first eng. a 396 punched to a 402 with flattops a 525 lift cam 750 carb. steel crank o49 heads. but id does not have the power that i thought it would so by chahging to a rec. port head help me that much and how much more hp. thank you jim 1BadRat Nov 19th, 02, 3:32 PM First off, from what you said, the flat top pistons concern me. You have open chamber heads(122cc, I think) and I bet your compression ratio is low. I don't think open chamber heads use flat tops. You need 9.5-10:1 with a cam like that, maybe a little more than that. The old 325-350 horse engines had 10.25:1. A simple fix would be to find a set of closed chamber oval port heads. I think you'd be suprised! http://www.chevelles.com/forum/smile.gif I think rectal ports would be a bit much. I would use rectals only if they were closed chamber, and if that was all you could find. ----------------- -Mark "Some of us got it and some of us ain't." -Deputy Sheriff Barney Fife TC# 717 ACES #1641 1967 Chevelle SS396/375 (http://www.chevelles.com/showroom/1BadRat2) 1967 RailVelle (http://www.chevelles.com/showroom/1badrat3.jpg) 1964 Chevelle 283/195 1975 Corvette 396/425 (http://www.chevelles.com/showroom/1BadRat1.jpg) "Wow, that's a mighty strong 350!" Rat Garage (http://www.chevelles.com/showroom/RatGarage.jpg) [This message has been edited by 1BadRat (edited 11-19-2002).] Mike Feudo Nov 19th, 02, 3:34 PM You got no compression. A change to closed chamber big ports will help the compression but nothing else. Find a set of closed chamber ovals for an early 396 and use them or change your pistons. 1966_L78 Nov 19th, 02, 3:54 PM Oval versus Rectangular, with similar chambers (and compression ratios) will not give you any improvement until upper RPM. Probably a little drop in performance in low to mid ranges, especially on a "small" 402... The rectangulars will flow more fuel overall, but will only make more power if your engine can use the extra fuel (high RPM or big motor)... Get a head that corresponds with the pistons you put in (just as the others stated above)... ------------------ "Once you go RAT, you never go back..." TC #1366 Tony The Chevelle (http://www.chevelles.com/showroom/1966_L78/ChevelleA.jpg) Dual Quad 396 (http://www.chevelles.com/showroom/1966_L78/ChevelleC.jpg) Side View (http://www.chevelles.com/showroom/1966_L78/ChevelleD.jpg) [This message has been edited by 1966_L78 (edited 11-19-2002).] | ||