it all depends on the turbo and what its capable of...wont get much if you have a 3 inch turbo outlet flange and go 4 inch in exhaust. Gotta increase flow from the source then work your way down.
could be anything...loose or cracked vacuum hose, bad maf, bad o2 sensor, loose electrical connection, poor sensor ground, or faulty cam position sensor. Those are the main things that will cause a car to run erratic.
I purchased one of their kits (clean-injection) for my 240sx with rb25 engine about 2 years ago. Came with the sard regulator that looked pretty genuine to me. I purchased the bosch 750cc injector with fuel rail to fit my factory intake manifold. Actually really pleased with the quality. My car is making a happy 625whp on e85 no issues at all. Idle is rock solid. I plan on upgrading my turbo to go for 900hp soon...will be contacting them to see if they have some bosch 1000cc injectors to do the job.