Need to go faster after disappointing drag race(whistle?)

[Twilightoptics]

So I finally hit the strip with the 7. It's stock, emissions removed, no cat, 30,000 miles on a pineapple rebuild. Only mustered 17.25@79.20MPH @ PIR

I sure thought it'd be low 16. No wonder I got beat by a stock 4dr Cobalt the other day.

So everyone seems to agree the RB header is the way to go. I'll do the rest of the exhaust work myself and use a straight through muffler. 2.5" stainless back.

What kind of realistic gains can I expect to see? RB says %25.... that's about 25 horse. Really?

Also when I get on it, I think after I feel the secondaries open, there is a knarly whistle. Almost sounds like a turbo. Friends in the stand says it's super loud and super high pitched. Now I've got the shutter valve disconnected. Is this a normal whistle, or is it the engine saying that at about 4k It can't flow any more?!