Velocity Stack
 

I wonder how much improved response one might get?

I found someone mention this:
"Think about a turbo car is the air flow is ultimately kept in check by the wastegate, so the few dyno we have seen with stacks on the compressor side, generally improve turbo responsiveness, with reduced lag and faster spool up, but we have not seen any significant gains. Data is on boost Honda and 1.8T VW and Toyota MR2. I believe we have charts on the 1.8T, power gains were minimal. Honda was test by St00pid (aka Jason Herrera) a local tuner, I did not see the dyno results. The MR2 was based on log data."

Um, well the whole idea is that you'd get faster spool and less lag. Not sure what "hp" numbers they were looking for, seems Velocity stacks would really only provide one where it is the bottleneck or highest resistance in the system.

Dunno how much improved response, it's kinda a...subjective rating.

IMO velocity stacks help the most in smaller displacement well flowing NA engines, our engines have other issues that will minimize any gains you may see from these, i.e. not so well flowing head.

Are you talking about the intake runners, or like a bell-mouth for the turbo?