The SR engine have the t-28 turbo as its std, u say u got exhaust from the elbow, hope u planing on changing the elbow really soon, its make a hell of a backpressure to the turbo at 1 bar, kill it in no time, and a mayjore hp killer.
Since the first thing the exhaust will have to go thru is the elbow it should not be any backpressure threre + a good downpipe they should be 2,5-3inch
insted of the std elbow beeing 1inch inside.. The exhaust manifold should manage 300hp but a aftermarked one will make much better flow=hp and responce..
The MAF i know people been over 330hp with.. My blacktop SR puts out 295hp-ath at 1,2bar and 410Nm with the std turbo and MAF
If u use the car for dayli juse, u can run 1 bar no prob, 1,2 i pressuring it, but people here in norway been driving with 1,2bar on std turbo for 2-3years with out problem, but MUST be good exhaust ALL the way, and its not a pure track car..