turbo or something is leaking maybe?

hi guys ! well i'm new in this web and i'm looking some advice for my engine ! i'm searching actually why my engine is in very underpower ... felling it jz like turbo lagging or something leaking ! i'm driving a nissan cefiro with R32 skyline engine ! well when i try to speed up ... sometimes
it will very smooth n sometime lagging cz i heard from the exhaust is poop-poop-poop sounds coming out .... and if i still boost it then suddenly the will speed up ! huh god wat happen !

sorry if the english poor but much appreciate there i can get u guys advice ! :screwy: