If you were to take a new Victor, scribe the MR gasket, and just blend the last 3/4 to 1 inch at the port, you would have a very good street manifold. That would give you 390-400 cfm, of fast air. If you wanted a very strong manifold, go in the port 3 inches, and just bring the walls out parallel, and keep the height equal all the way through the pushrod area, and then blend to gasket size the last 1/2 inch. If done properly, this will give a MR size port that will flow roughly 440 cfm. Blending of the plenum straight down from an open carb spacer, and rounding any rough slag in the plenum area will give you the 450 cfm. If you have a stage II head that flows 320 cfm, this will be just about perfect for street and strip for your 489CI. Joe-JDC.
