i reckon you would find that the port in the inlet manifold would be closely matched to the throttle body size, and that bolting a bigger throttle body on will just bottle neck, IE squeezing 68 cubic mm of air through a 65 cubic mm port.

I reckon its funny how SS inductions sell Massive T/B's for LS1's for $600 but dont tell anyone that the hole in the manifold is only as big as the stock T/B, I worked with a guy that bolted one on, spent $600 on it, and noticed no difference what so ever.

iuf you open up the throttle body more do you need to fit a larger butterfly in therE?

The intake to the manifold is big enough to fit a ported throttle body without restriction. Depending how its ported, you dont need a larger butterfly. For most people though there are no gains to be had though. As said above, the stock TB is already big for the size of the engine. It wouldn’t matter if you fitted a 68mm or a 90mm TB you are not going to gain anything unless you engine is VERY modified.

In fact, many people (including myself) have found you will lose power by fitting a larger throttle body - presumably due to the decreased airspeed into the manifold.

ive got one aswell!