I'm building my block, dropping compression from 10.5:1 to 9:1. My problem is that I'll need to break in my new clutch before I retune. How will the drop in compression affect my current tune? I'm guessing that since I'll be running the same boost and fuel trim nothing will change at all as far as a/f ratios are concerned.

 

the 9:1 motor will take a good bit more timing.

 

Oh I know it will take more timing, it'll also take a hell of a lot more boost. My question is will the a/f's be the same, and if they will be different will they be richer or leaner.

 

bump for an answer

 

It'll change. I'd atleast get it slightly tuned or something. Just make sure you don't run rich and wash your rings out.

 

bump for a definitive answer.

 

it WILL change. If you leave an O2 sensor enabled, it would probably be enough to take the car out and drive it with no problems.

 

richer or leaner?

 

Honestly it all depends, but I would say it SHOULD go richer.