Quote Originally Posted by 1project2many View Post
Some people, myself included, believe the commonly available TBI to Vortec intake manifold is a copy of an OEM intake installed on vehicles which were exported in the mid-'90s. As such it offers relatively small peformance gains. It's possible and effective to increase the diameter of the opening but most folks don't opt for this solution. Instead they use an adapter to bolt on a 454 TB. The adapter spaces the TB up and does allow some cross-bore airflow but it's not the best solution.

The carburetor manifold with adapter is method to allow maximum airflow possible. With a TBI in a street application it can be important to balance airflow with air temperature and plenum size. There are several ways to do this but a good one might be to find a manifold with a smaller plenum size. There are race manifolds for Ford or Holley 2bbl intakes which can be a good choice with an adapter. Edelbrock 2912 is one possibility.

Another option is to use a spread bore Quadrajet style manifold with an adapter. These manifolds typically provide some coolant heating and do not raise the TB as far out of the engine valley. There are aluminum and high-rise cast iron versions. Edelbrock, Weiand, and Professional Products all make manifolds in this category.
I also feel the GMPP Vortec TBI manifold is a copy of a factory manifold. Either the Export manifold or the GM Marine manifold. I have seen a very similar manifold used on Crusader 305 and 350 engines and they are stamped Crusader.

In the past a 2912 ran very well for me. I used a water heated Holley Projection TBI to 2bbl carb adapter that was available at the time.