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Old 08-22-2010, 08:06 AM
oldngood oldngood is offline
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Originally Posted by lust4speed
You first stated that you wanted a mild cam to avoid detonation, but the opposite is true since the hotter cam bleeds off some of the initial compression since it keeps the valves open a little longer. A safe approach to compression is to have a total of 92cc's total combustion chamber and piston relief for regular gas. If you use one of the less expensive rebuild kits that have the cast pistons with the multi valve reliefs cast into them, the total "dish" of the piston will come out to about 12cc's. Take the 12 and add it to the 72 cc's that the 62 heads might be after a cleanup mill, and you have 84 cc's or about 9.2:1 compression. Premium fuel territory, but acceptable. The alternative would be to get a set of relatively inexpensive TRW forged pistons and have your machine shop cut a 20 cc dish into the top of the piston.

I just put together a 421 that was .060 over with a set of well worked 62 heads, and 26 cc dished pistons (bigger engine requires a little more dish). we installed the Summit cam and lifter kit and are really, really happy with it. the Summit cam visually looked better than several of the big name brands we have installed. This is in a HEAVY 1965 Pontiac 2+2 that weighed in at 4,418 pounds with driver at the drag strip scales. We run it on 87 Octane pump gas with no pinging. We participated in the High Performance Pontiac Magazine shoot-out on June 30th at the California Speedway POCI drags and the article should be coming out in a future issue.

the bigger cam bleeds off compression at idle or part throttle low rpm, but not at high rpm- those big cams "come in" above 3000 rpm, then the engine is detonating harder than ever, and actually doing some serious damage. That is not the solution, the solution is what you did, dish your pistons, which no doubt you gleaned from other posts elsewhere on the net, for a Pontiac. I run a 470 CID Pontiac with 80 CC heads, and dished the pistons 30 cc, they are TRW's flat tops- and I posted the results and pictures on the net of the parts. Back then everyone was pushing "quench" and 10:1 CR which will NOT WORK with today's gasoline and iron heads. I lowered the CR to 9:1 and the engine actually makes a lot more power, because now I can rev it and dial in 34 degrees total timing without ping.

the big cam fix doesn't work, it only kills the bottom end, and the engine will still ping above 3000 rpm

your 421 build sounds cool
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