Ring Sam's Performance(Greenacre nsw) and have chat to him, he is very knowledgeable on LS1, he told me the standard LS1 heads flow quite well, and that the standard cam is very conservative, but also the standard exhaust causes alot of back pressure, so fitting a free flowing exh system plus remapping the fuel plus dyno tune(cos it will run lean after the exhaust is opened up)will yield a big gain, and most commo enthusiasts are happy with that.
Just to give you an indication, my 5.7 VX II calais was 225kw standard, before mods, on dyno it was putting 178rwkw, after the exhaust(including extractors and new cats) and dyno tune and new oxy sensors, she picked up 42rwkw and extra 28nm torque, if you do the math, thats 220rwkw, or 270kw@flywheel, goes like stink now:rockon: but my next mod will be a lower diff ratio.