im new to cossies so help me out

my 2wd saph backfires & splutters at high revs so whats the crack there as its hampering its performance a bit & the boost is peeking at around 14psi

it has green injectors, bajoo chip, rs 500 intercooler, collins actuater, 3 bar map sensor, k&n & stainless exhaust & maybe a hybrid turbo but im not sure, has dyno graphs for 340bhp

im thinking maybe a set up as it sat for nearly 8 months plus, i havent changed the plugs & leads yet either

cheers