Why does my powerband look so terrible?!

Hey all,

Just got my GTO on the dyno and was kinda shocked at the power curve. The numbers themselves don't concern me, but I've never seen a dyno graph look like this. My tune and scan of the pulls are also attached. The power seems to be falling off BAD after 6200 rpm. All my relevant mods are in my sig. I'm thinking it might be valve float from either weak PRC dual springs, these comp 1.75 roller rockers, or a simply the AI 243 heads not able to keep up, maybe a combo of all three?? The springs are about 4 years old 25k miles, the lift on the TX Giant cam is around .640 with the 1.75 roller rockers. The springs are rated to .650

What do you guys think?

http://imagizer.imageshack.us/v2/640...539/e8ad02.png

Unlocked through a 4000 stall? It's difficult to ascertain good info from a short pull like that through what I presume is an unlocked largish stall, but apart from add anomaly at the end doesn't seem unreasonable. Although those springs don't bind at 0.650 with the 1.75 ratio rocker, you will have greater than 0.650" lift assuming that 0.640" is quoted for 1.7 ratio.

I see how the auto and big stall affects dyno numbers. Just the curve does not look right to me. The lift of the cam is at .640 with the 1.75 ratio factored in. I have heard some aftermarket rockers are heavier which could cause valve float at higher rpms. Is there a way to tell though. The scans show nothing I can see and the motor sounds fine at high rpm...just falls away on power.