Q's about PI Swap
 

I've heard that if you get a PI head swap that you will need to start running 89 octane gas instead of 87 is this true? I heard it was because of the higher compression. How I understand it the PI head swap is mainly 3 things, the intake, cams, and heads. If you do need to run 89 octane with the PI head swap what part of the swap increases your compression so that you do need to run the higher octane?

RE: Q's about PI Swap
 

well, first off the PI heads have a smaller combustion chamber than non pi heads. so, when bolted to a non PI block, they raise compression. 4V heads have big chambers, and would drop compression, for example.

you'll be running @ 10.5 to 1, and even if you do a stock head swap, you'll still need a tune for best results. wich, with that compression, will require 91-93 octane, wichever your area has. you can do an untuned swap and run off 89, but i wouldnt. that's just too much compression for a lower grade fuel.