Ok now im working on a tune for my new rebuild. I'm doing diamond fully coated pistons, rods all that good stuff. I was running 11.9 with stock pistons. Is that still a good number with my new pistons or can I go leaner 12.5 for example.

 

You can go leaner than 11.9. I was running that with 10.4 compression on my 2.4l. Richer mixtures are safer at the cost of a little bit of power. Pistons won't change the AFR you can run unless the compression ratio has changed.

 

oh ok for some reason i thought if u ran forged pistons and all that it was possible. well ill just keep it 11.9 then. i may go richer wen i bring the nos in to be safe.