I just got myself a 5.2 tb for my 3.9. Ive read the posts od people swapping them after modding them. My question is why do people cut off the...what id describe as a velocity stack, the raised lips around the bore? Id that for flow gain? If so has it shown measurable power? or is it just for looks?

 

Im pretty sure its for flow gain but the person you want to talk to is bwdakrt he modify's them all the time.