Compression Ratio how to...

[Codydubb]

i bought this car with the engine already built and i dont know much about it, it looks like its boost ready and im more than willing to go boost, but i would like to know the compression ratio..the only way i know how to is by figuring it out with your cylinder heads pistions etc, i heard there are other ways by measuring volume or something? any advice tips tricks suggestions would be much appreciated, the only thing i really that might aid me would be the heads which i have a receipt for, all the other internals i have not a clue!

 

[tannerc91gt]

what do you mean by "looks boost ready"? and theres a formula to follow for CR, but there are online calculators if you're looking to make it easier. there's quite a few specs you'll need to know, and would have to open it up to do it (unless you're sure the shortblock is stock) such as HG thickness etc. But once you've figured swept volume and all the other fun little equations the best you'll get without all the specs is a ballpark estimate at the static compression.

There have been claims that a compression tester and yet another math equation can get you the number you're looking for, but i'd have to see it to believe it.

If you want, Give me some specs like what heads and other mods relating to compression and ill give you a number assuming stock shortblock and standard HGs.

 

[txstang84]

+1 what tanner said...

Measuring pressure won't give you a mechanical CR unless you know a bunch of variables. It will, however, give you a good indication of whether or not your rings are wearing evenly. The only ways I know of to accurately measure your CR is to at least pull the heads and see what pistons you're using, head gasket thickness as mentioned above, piston deck clearance, etc.

You can ballpark it with assumptions, but unless you take accurate measurements, you can't know for sure. If you want to play around with some numbers though, here's an online calculator I've used before...

http://www.torinocobra.com/Randys_tools.htm

 

[Codydubb]

By boost ready i mean the previous owner told me it was ready for a supercharger but couldnt tell me anything about the internals i figured there was no way without pulling the heads which i dont want to do at the moment, it has Msd BTM on it but i dont want to go throw boost to it without knowing whats inside

 

[tannerc91gt]

the previous owner told me it was ready for a supercharger but couldnt tell me anything about the internals

seems like a giant contradiction to me. I hate to generalize but a majority of the people ive talked to about their foxbodys (especially when they're selling them) have no idea what in the hell they're talking about....

if you're actually serious about putting a blower on it, you're just gonna have to pull the top end off. simple as that