I have a 1996 lt1 stroked 385ci forged engine, match ported stock heads and manifold, bolt ons, cc503 cam, stock inyectors, lt1 edit, 1.6 ratio rockers, stock fuel pump and regulator.

I was wondering if the 48mm tb would need to be upgraded to a 58mm one?

should I use a adjustable fuel pressure regulator to rise up a little fuel pressure not maxing out the inyectors? would the stock fuel pump handle this?

 

You could probably benifit from a larger TB. I think you are close with a 383 and a moderate cam.

 

A 52mm TB would probably be adequate. If you push it over 500HP at the flywheel, then look at a 58mm. But if its running stock injectors, and stock fuel pressure, you are nowhere near 500HP at the flywheel.

Attempting to run stock injectors on that engine is risky. A stock injector will exceed 90% duty cycle (not a good idea) at about 425 flywheel HP (exact HP limit depends on how efficient your tune is). Rather than diddle with the fuel pressure, just put a set of 36# injectors in it. To turn the stockers into 32's (for example), you would have to increase the fuel pressure to 73psi. The stock injectors do not work well at that pressure, and the stock fuel pump isn't going to flow enough fuel at that pressure.