"Hey guys new on the forums here. Have a 05 gtp, with a few mods. I was wondering if I could run a 3.4 inch pulley with everything I have, colder plugs, 180 t stat, k and N cold air, zzp headers 3" dp with an electric cutout, and a box tune and egr delete"
You MIGHT be able to get away with a 3.4. Do you have something to scan with? Such as an aeroforce or scangauge? Monitor knock and if you don't knock then you should be fine on a 3.4. Also, get a legit tune when you cam/IC. A tune specific for your car will be a lot better than a canned tune.
