Here's one thing nopt mentioned - the effect taking the turbulator ring out has on estimated hp gains. I understand that is about 10-15 hp an that the manufacturers include this in their overall publication.
I took mine out and it sounds better, but did not notice much - MAYBE another 100 rpm but who knows. Sound was a little better through. I heard this in another thread so if a manufacturer claims 50hp increase over stock - maybe it's more like 35 to 40?
Has anyone dyno'd a stock manifold with the rings out? They do restrict by about an inch on each side.