I dont know if they give you any power as much as they give you better air flow, allowing you to add fuel and thus, more air to make more power.
Daniel
His- 93 W250 club cab LE, auto to Getrag conversion, piston lift pump, 3.54 LSD. 400k+ Hers- 04 QC 4x4. Built auto, Triple Dog, Air Dog. Funny Round truck that aint so quiet.
i can tell you we put a stock head on the flow bench at work and nothing over stock lift increases air flow on a STOCK head. so if its not ported i would say no. it will give you quicker spool so power will come on sooner but flow went down over stock lift. again on a STOCK head unported
93 w250 reg cab. rigged up stock downpipe to 4 inch to 5 inch exhaust from p.o. mild pump tweaks and all other stock for now. Project "smoke a little smoke". www.c-techperformance.com
Pretty much what mprmn08 says you will get quicker spool your drive pressures will increase as well. They are keeping the exhaust valve open longer in most case to add more flow to the turbo.
Your truck will run cleaner and you may be able to run a larger turbo.
I am in the process of working out drive pressure issues right now but the truck picked up .60 in the 1/4 mile and it was much hotter out then my last run.
The truck runs much cleaner off idle then it ever did turbo lights almost right away.