I have a 2006 Grand Prix GT (supercharged) and am wondering if I need any PCM programming in order to fit a 3.4" supercharger pulley without throwing any codes or affecting my KR?

I installed a 3.2 inch pulley on my GTP and I didn't have to do any pcm programming I also put on an exhuast and a intake at the same time so far i don't have any knock, also a 3.4 inch pulleyis a lot easier on the motor than a 3.2 inch

Scan, scan and scan.

Everyone's setup is different. From climate to variations in tolerances from engine to engine (some are just lucky motors and quick from the factory - while others, not so much).

Typically, 3.4" needs downpipe, thermostat, intake and maybe exhaust work to avoid knock. But from what I've seen the 2004 SC motors (with the electronic throttlebodies) run smaller and with less KR than previous gen L67 engines.

So back to my original answer. Mod - then scan, scan and scan. Otherwise what someone here installs and gets away with - may blowup your motor.