when is there a need to upgrade the stock LT1 intake manifold power wise.. someone told me when you're pushing over 400 though i've also heard it's effective over that... anyone know?

 

It's not so much power-wise, but RPM-wise (I suppose they are one in the same). I run a ported stock manifold and am pushing 550+fwhp just fine. A buddy of mine will be closer to 600HP N/A and is using a stock ported manifold also. Fortunately GM gave us a manifold that works incredibly well.

The only time I would consider upgrading is if I was consistently spinning to 7k+ and had the valvetrain to support it.

 

Upgrade it to what? You can port it a little or spend a lot to have it extrude honed. You can get a 52 mm throttle body or open up the throttle body ports and get a 58 mm throttle body but it's not needed at the power level you'e talking about. The Eldelbrock manifold isn't an improvement over stock. Neither really is the LT4 unless you have the heads to go with it. If you really decide to build a wild engine you can get a sheet metal manifold or get a single or dual plane carb manifold, but again, that isn't helpful for you. Just leave it alone for now