hi all I just bought a bbo that needs a rebuild . it has low compression pistons in it can I put a set of stock high compression pistons in it with out having to rebalance anything?. im trying to find out what my stock low compression piston weighs .I was told I can go 3% heaver or 7% lower on piston weight without any changes any input would be appreciated.

 

I dont know the answer to your question, however if you have the pistons out then you are very close to having the crank out too. Balancing is one of the cheapest and BEST things you can do for an engine. Especially if your building a "high compression" performance engine. Others will know the answer to the question you asked.
Good luck
Steve

 

Who told you that?

 

a mechinist sosenson performance can u give me more input.

 

Before what happens? 3% of a 750gram piston is 22.5grams. You'll most likely feel that. And although an imbalance on the heavy side is less of an issue, I guarantee you feel the 7% of 750grams. That's 52.5grams. You'll feel that no doubt. And it'll negatively effect bearing life at that level as well, guaranteed.

He pulled those figures out if his butt. Get it balanced, but not by him.

 

I have to have the cyclinders bored out .030 could some one recommend a good set of pistons to put in my 455 they had low compression in them id likem to go to a higher compression piston and still use pump gas ill be putting c heads on the motor and using a comp cam h274 cam

 

Either Icon IC886 or equivelant Wiseco. And with stock C heads I'd do a different cam.
I'd still find another machinist based on your earlier comments as well.