Won't make over 15psi of boost

[litdog83z]

and only picks up 16-17 mph from 1/8 to 1/4...

Feels pretty flat up top, so i'm thinking the stock valvesprings are the culprit. Would stock weak valvesprings make it where I can't make more boost?

My car has 170k miles on the stock engine, but the heads were "reconditioned" at the dealership by the original owner a few years ago. I'm not sure if that means new valvesprings, as they were just having a problem with a valve/seat.

Also the car feels stronger at lower throttle than it does at WOT

 

[441120]

Don't know if springs will limit your boost, but they will kill your top end.
Any scan data, or F/P readings?

 

[litdog83z]

750-770 o2s through the traps at 90 mph, somewhere near the top of 3rd. 0 knock on the whole run (running 91/110 mix fuel about 60% 91 and 40% 110 cause I planned on playing with a little more boost if everything went alright)

Car is mostly stock, upgraded fuel system, TT chip burnt for 91, dutt neck IC, power plate, hooker catback, solid MAF pipe with K&N.

Another guy I know says it's the crack in the header, and I know that's not helping me much. I just figure the valves are floating some from the weak springs and it's not pushing enough air until very high RPMs to creep the boost up some.. It's possible that there's a leak at the intake at 15psi of boost, because when I installed the power plate one of the bolts started to strip a bit, but was still snug so I left it... I'd think that I would hear some noise if it was leaking boost at 15psi + though...

 

[litdog83z]

btw fuel pressure was at 43 psi line off per TT chip recommendation, but it was trapping over 800 o2s and bogging really bad just off the line (seems like it was at the top of first actually... maybe the valvesprings were a conributing factor here), then it would be even flatter at the top of third and bog some... Turned the fuel pressure down to 41 and it stopped bogging down, but still felt flat up top. o2s were at 780 that run, so I turned it down to 40 psi, didn't go any faster or feel better (trapped at 750 o2), so I put it back to 41.

Seemed to run alright otherwise, no knock the whole night and no hiccups of any sort.