I am building a new motor for my car and was just curious if anybody knew the gains i would see from porting the heads.

 

The short answer... around 10 percent more power. That's just a good rule of thumb for porting and polishing heads.

The bad news is... 3.0 heads don't flow that well. And to really see a 10 percent improvement, you need a better ser of cams and usually valve work to go with this. Furthermore, you'll need something to help with the flow--some sort of engine tune.

 

3.5 swap nub.

 

If you enlarge too much you will slow the velocity of the air coming into the combustion chamber (=bad). Polishing and smoothing the edges would be beneficial but by probably just a marginal amount.