could just be boost leak.Have you ever taken ur turbo off or maybe upgraded to a custom turbo manifold? I did and it gave me some simular issues due to shotty gaskets,fixed it though.And look at the flipside,if ur turbo burns out its time time upgrade! May a suggest a T3/T4?
theres a difference,couldnt tell you what it is though,I hear the top mount manifolds are better than the bottom mounts,but I think its all about preference,its jus easier to get to your turbo if youre top mounted.Ive got a custom manifold on my RB,saw a slight increase in get up and go,bottom mounted though.If you buy a top mount designed turbo u gota buy a top mount manifold for it,$100+ on ebay all day long.Suggest you buy an electronic boost controller if you dont all ready have one,Ive watched friends of mine grenade their SR's due to upgrading the turbo and overboosting.can you say "GRENADA!!"?
Top mount manifolds place the turbo parallel to the head and allow you the freedom of turbo choices like size and type(depending on the manifold itself) Bottom mount manifolds restrict certain size turbos due to space constriction near the crank case. There are no top or bottom mount turbos only manifolds
Ive heard that some turbos are designed to be topmounted,though ive never seen one that demanded that kind of specification,ive never really looked into it,personally i jus wanna see if I can get 300hp while still armed with my stock turbo,then ill upgrade. So top or bottom mount manifolds are simply a matter of preference,right?