2nd and 3rd gear not holding boost

[indebt240drift]

any one know why an sr20det might start backfiring once half boost is hit in second gear...i know stock sr's only put out 7psi, so ive been told, 11 if you remove something, but i just put on a boost gauge and its reading 16psi when i rev it to 6 grand!!!!!! it only does it when im on tar also, if im burning out on tar, or on dirt with no traction, it doesnt do it, anyone with any knowledge wanna chime in , itd be appreciated