compression ratio

[Cobain03]

i need a quick answer...

im getting the 289 rebuild, and bored 30 over and i think flat top pistons are going back in. wats a rough estimate on the ratio?

 

[Bullitt]

better tell us what heads you're putting on it as well...

or combustion chamber size...

 

[iskwezm]

also gasket thickness, have the heads been milled? block decked?More to it then just flat top pistons.

 

[Bullitt]

decking will have an effect, but it will be really minor compartively (at least on a big displacement car, a small engine like in a motorcycle is a completely different story). gasket height is also important, but it's more an average thing that your average engine builder won't know beyond what the manufacturer says.

 

[Cobain03]

stock heads, i belive heads will be decked as wel as the block. and i guess average gasket size

 

[rbohm]

well stock with flattop pistons, the 289 came with a true compression ratio of 9.5:1. with the work you have had done, it sounds like your compression ratio is going to work out around 9.8:1.