Thread: compression ratio choices

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i have changed my mind about building my 454 i originaly wanted a low compression engine for a forced setup but i think i am gonna buy new pistons and sell the -4cc dish pistons i havnt used yet, does anyone have any suggestions for what kind of piston i should buy and what compression i should sit at? keep in mind i still want to use pump gas and it is daily driven. thanks
sean,


30 over
781 heads (stock except for polish)
power plus cyclone manifold
holley 3310(proform main body)
th400 3.73's
78 camaro 3600lbs.
street driven
full length headers 2in. primaries 3.5 in. collector

Pump gas and high compression don't belong in the same sentence. Much more than 9.5 and you're looking for trouble.

You can make a lot of horsepower on a 454 with 9.5:1 and some good heads. 500+ hp.

i am having a hard time finding a set of pistons that give me a 9.5:1 ratio can anyone find me the dome i should be looking for? the 781's are supposed to be 119cc open chamber? i dont have head gaskets yet so i can also work with that.
i have already had a set of .340 dome pistons but i returned them because someone told me they were going to be too high. so i am at my wits end trying to figure it out and if anyone can help me i would really appreciate it.

p.s. anyone want to buy a set of speedpro hyper u's -4cc dish

Sean, I dont know where you have been looking, but I just looked in a Jeg's catalog and found three..you're looking for something along the lines of a .215 or a little bigger dome. KB hypers, #207...these will give you about 10/1, OK for pump gas. Speed Pro, LF2465, they yield 10.7 w/ 107cc, so with your larger chambers, you would be at 9.5 to 10...Speed Pro hypers, H693CP, 10.3 with 107cc, so about the same as the other Speed Pro's...there are more. You can run 10/1 without problems as long as you run the highest octane you can get...dont use 87, that's all. Your carb and gearing look good, but those headers area little big for the rest of the combo...1 3/4 would give you more torque down low where you need it. Also, what is your deck hgt?? That will have quite an effect on your c/r, much more than the head gasket. John

i dont know my deck height, how do i find out?
and about finding the pistons i found some but the dome size vs. c/r was inconsistant with each brand thanks for the piston choices also with the headers i havnt bought them yet but when i try and find some full length to fit my application 2in. are my only choice unless i pay a ton for the headers or go with the mid length, what do you think i should get full or mid?

Unless the block has been machined before, your deck hgt is probably stock, usually about .025. That will lower your c/r a bit more, as the specs in the catalogs and literature usually assume a 0 or near zero deck hgt. The piston choices will always read a bit inconsistantly, each company will write up their products a bit differently. You have to estimate based on what you have now, or will end up with after any machining work. Thats why it is important to know all your measurements before you start to build, or even to buy more parts...your deck hgt, head gasket thickness, combustion chamber volume (dont go by the published figures), all these things will effect your c/r quite a bit. You really have to know where you're at. As far as the headers, I dont know about the length, not familiar with that part of the equation...but I know too big a diameter will move your torque curve way up the rpm range.