Things don't get as technical as specing turbos lol this is very much a budget racer turbo and exhaust manifold come from a st170 turbo I got as unfinished project so I just used all the doner parts from that really . As in compression the engine is completely standards no decompression plate nothing . i do think the turbo is over sized but dont think thats the problem here ever at full boost nearly 6000rpm its still only just over 170bhp ment to be 7psi spring in wastgate but creeps to about 11psi