Tom. Mike, those are dual 409 carbs. and they are taller than the single 409 carbs., plus, they are usually more money than the front carb. and are "pretty much" a dump carb., less air screws. Pretty much, all pass. Car Pontiac "D"- Port Heads have the same size Ports. If your Ports are bone stock and there is no telling if they are, the reason most tend to Port match, is to properly match the Intake Manifold to the Head Gaskets. With Pontiac SD Carbs. and Pontiac dual 4 Linkage, you can set them up progressively, so that the Car is running on the front of the rear Carb. When you get into them, the front Carb. will come in first and at full tilt and all 8 Carb. Bores will be open simultaneously. Thus, the reason for the progressive Linkage. Some people like the Solid Linkage, so both carbs. are on the same opening. I HATED that on the street! Tom.
Thank you for the explanation, Mike.
Last edited by TRADERMIKE 2012; 02-26-2022 at 03:27 PM.
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