Do you think my turbine housing is choking my engine ?

I drift a BMW E30, I have an M20 B27 with a b25 head 272 camshaft, I o-ringed the block, forged rods but cast pistons for now..GTX 3076R turbocharger with 0.63 AR turbine housing and a 45 mm external wastegate with good priority, 3-in exhaust and a 24x12x3 intercooler... EMU classic ... What I see in tuning it is that between 4,000 and 5,500 RPM my fuel values are the highest say 131 is the value approximately in that area at 250 KPA and then drop off from there considerably to 7,000 RPM to something like 121...I think this represents a downturn in VE I have bought a .82 AR turbine housing which I'm going to put on I also feel like this camshaft is a very low RPM to mid-range cam and I'm wondering if I'm pushing against it? I may just retard the cam a tooth as well...I I set the camshaft one tooth retarded by accident one time before and felt the engine actually ran well higher in the RPM with little loss lower in the RPM... I believe one tooth represents seven or eight degrees of camshaft timing.... I machined the cam sensor plate on this engine and put together this valve cover with LS coils... built the downpipe and exhaust... My thinking was that running a good size wastegate with decent priority get away with running a smaller turbine housing. I think It's choking the engine off And just wanted to ask the opinion of other folks.....

Thank you for your time....

Jak Stoll

Measuring exhaust gases back pressure would tell you exactly if your turbo is choking the engine. Changing turbine housing with bigger AR helps to reduce it but not too much. The biggest back pressure reduction usually comes with changing for bigger frame turbo..

George thank you very much for taking the time to respond to my question :-) I very much appreciate it. I believe I am not really near the horsepower limitation of this turbocharger, I do not believe that I am exceeding the frame size due to engine displacement but I agree with you that going up in frame size will help me move the power higher in the RPM.

I'm going to retard the cam timing tomorrow And try to ascertain the effect of that on my VE higher in the RPM, I have a feeling that the drive pressures are getting kind of high but I do need to put a port on the exhaust manifold pre-turbine so that I can measure my drive pressure .... I have the .82 AR turbine housing here it's just a little more difficult to change because I have to weld the wastegate flange and tube to it....

Thank you again for the input

Jak Stoll