Injuneer

58mm TB / bored 58mm (LT4) intake

doritoboy100

So I would need to bore the throttle body out to 52mm? And if I'm already having my intake worked anyways I would just have it bored to 54mm and get a 54mm throttle body to go up to 54mm.
I am trying to keep it on the cheaper side, but some of these aspects are going to have to be changed anyways (I'm going to have to rebuild the transmission regardless, and I'm going to have to replace the water pump and ignition system components as its misfiring, and suspension needs to be redone as it's making a lot of noise) The wheels and tires aren't 100% necessary. But to upgrade the engine I will need to upgrade the rear end to take it, so the engine transmission and rear end work may be all I absolutely have to do, the rest can be taken piece by piece and upgraded.

Chimera96

you do not need to enlarge the TB ports on a stock LT1 intake manifold if going to 52mm TB. I thought stock intake was 54mm but Injuneer corrected that saying it is 52mm.

stock TB bore is 48 as noted

Given any aftermarket TB does not have the IAC inlet port many require some "alteration" to get car to idle right which requires having the ability to scan the car for IAC counts before ANY modifications to a aftermarket TB should take place

a 52mm TB will be more than sufficient for a 383 build under 500 hp. A stock TB re-bored, IMHO, is WAY more plug & play relative to getting IAC counts right. You "may" need to drill out the stock 1/8" IAC hole 1/64" bigger "if" after scanning the IAC counts are higher than spec at idle (30-32)

you also need to have the pcm tuned for a larger TB if you have a automatic trans...or tranny failure will soon follow