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Old 07-20-2005, 12:17 PM
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400 small block compression

i am putting new heads on my 400 sbc and i was wondering what compression i would have if i went from the current 76cc head to a 64cc head. Im not sure of the stock compression ratio but i think its 9:1 (each piston has a 9 stamped in it). THe motor has dished pistons. By changing to 64cc, what would be a rough estimate of my compression ratio? And also would i still be ok with pump gas?

Any chance i would get away with a 58cc head? I am looking to buy some reconditioned heads through an ad i saw in the back of chevy high performance called "Performance Heads"

HP GM Heads 474.99pr
Your choice 58 64 or 76cc 194/150 or 202/160 valve size, magnafluxed, bronze valve guides, 3 angle valve job, resurfaced, stage 1 ported (blended off seat into vavle bowl), cut for screw in studs and guide plates. Assembled with stainless vavles, PC seals, .510 lift springs

Is this a good deal or not? I am also going to move up to the 202s from the stock 194s


Last edited by 19nova72; 07-20-2005 at 12:26 PM.
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Old 07-20-2005, 01:40 PM
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you get almost 1 point of compression per 10cc ...
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Old 07-20-2005, 02:29 PM
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Moving to a 64cc head would put the compression ratio around 9.5:1 or slightly less, there are many factors as well as this is a ball park figure without exact measurements and a compression calculator. If you plan to change heads use the 64cc heads and make sure you have the steam holes drilled, otherwise it`ll run hot. I wouldn`t worry with heads I seen in a magazine, as these heads are all over Ebay, machine shops trying to make a fast buck off young hot rodders or hot rodders period that know little about it and it works, most of the 58cc castings I`ve seen are 305 heads with big valves stuffed in them without the chamber walls relieved which shrouds the valves even more and cuts the flow down more, flow is power, so a bigger valve wouldn`t help in this case it would only hurt. I`ve seen some even say on ebay that some 1974 185 casting number smogger castings were "vortec heads" and vortec heads weren`t even released until 1996. If you was to order heads from this company do your homework and know what your getting first. 1.94 valves are fine for a street machine and will work nicely with other mods. going with 2.02`s you likely wouldn`t notice any difference so don`t waste your money on 2.02 valves. the 400 small block in 1970 had 9:1 compression, afterwards it was 8.5:1 all the way arcross the board. 400`s have shorter connecting rods and a long stroke as well as a bigger bore, going over 9.5:1 compression on pump gas is asking for it to come unglued due to detonation. it is also important to remember, 400`s don`t like revs so don`t get rev happy with it either. Number 9 on the piston top has nothing to do with the compression ratio. Other mods you could do would be a small cam, valve springs to match the cam and a double roller timing chain while your in there. 400`s make a lot of torque even in stock form, so bumping up the compression, cam, headers, intake, ignition and flow really helps to wake them up and makes one a outstanding street performer, just remember, stay conservative, do your homework, know what your getting, and you`ll come out fine.
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