[Pampered-Z]

What other mods do you have. The stock intake flows well for the RPMs the LT1 run at ( below 7,000. Portnig the plenum/runners will have very little gains.

Can you post pics?

The front should be opened to match the throttle plates. Internally the runners should be opened up to match the heads. I have stage III porting on my intake and heads, they match Felpro race ports (mine match the Felpro 1207 I think ). Stock the plenum and runners have a semi ruff finish, when ported they would be smoothed.

The key to better flow in the LT1 intake isn't really the runner cc, the plenum isn't that big that it will support excess runner size. What you want is to rework the leading and inward edges of the runners to promote better air flow into the runners. Also the area under the injectors should be opened up to ensure the gas is being sprayed onto the valve and not onto the intake which could cause fuel drops to form (or puddling).

but with all the above said, The only thing you really need to worry about is that the a 58MM throttle body gasket matches the porting is correct, if the holes aren't right you could be close to the gasket edge which could cause vacuum leaks. There isn't allot of gasket surface.