Inliners International Forums General Discussion Hi Performance 307 Pistons

Is installing 307 pistons in a chevy 250 a direct swap ? What kind of compression increase should I expect with just a piston swap. Is there a certain 307 piston everyone is using? Is it a flat top with 4 valve reliefs or 2 valve reliefs or a true flat top ?

It is a direct swap.
With a flat top (meaning completely flat,no chamfer) w/4 valve reliefs you will get 1 more point of compression.


Unless you are running a BIG cam,,you would not need any valve reliefs..


MBHD

Watch out for the common stock replacement 307 pistons. They have a large chamfer cut around the perimeter (reduce unburned HC emission I presume) and sit lower in the bore than generally desired. Both conspire to reduce your compression and squish effect. If you just drop them in without decking the block I'll bet your static compression ratio won't be much different than factory dished 250 pistons.

Now if you can get true flat tops without the chamfer and get the deck height to match then you will be better off. If you find a source for such pistons let us all know please!