I have a set of 72 heads on my 70 455. I put a B4B intake on the engine and it made a hell of a lot of noise because the 4 small exhaust ports in the heads were not covered by this early model intake. My question is do these A.I.R. heads route the exhaust gas into the intake when using a factory intake such that i should plug them to avoid the mixing of exhaust with fresh gas/air mixture? Thanks.
The intakes used on 455's that had A.I.R., had air passages cast in them that ran the length of the manifold on the outside top on top of the intake runners. These were plumbed into the air pump, and then there were four passages that connected to the four holes in the head. These go directly into the tops of the exhaust ports. So, the exhaust and air did not mix in the intake, and both are completely separated from the air/fuel passages in the intake. The A.I.R. pump just pumped air into the exhaust ports only. Not sure why the Buick engineers choose to involve the intake manifold to do this. But yes, you do need to plug the holes in the heads so you don't have a very noisy exhaust leaks. I believe the center two holes are covered by the B4B intake and gasket, but I plugged all four holes on each of my heads just to be sure. I used set screws and tapped the holes in the head so that the set screws were just below the intake gasket surface. I don't recall what size is needed for sure. I just picked the size that I could just tap the holes without drilling them any bigger.
The intake channels were used for the smiley channel under the carb as an intake pre-heater for the carb. I have them on my A.I.R. -equipped 67 430 -w- big-port heads. I have another set of big-ports without the AIR channels in case I choose to switch. The hoses have check valves on both heads, and a gulp-valve on the rear port of the Q-Jet to minimize backfiring (doesn't work if engine is cold).
