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Have a concern with a hole at the bottom of the small bore for the upper plenum... The intake is 73/74 455 embossed with the OLDSMOBILE logo... I have never noticed this before and just thought I would ask the question... Is this an issue/concern??? Looking at the design, the hole will allow some of the fuel meant for the upper plenum to flow to the lower...
From reading a little, apparently a fitting was in there, and yours rusted a little and lost it. Regardless, it's a hole. That hole does not go to the other half of the plenum, like you noted, it goes into the exhaust crossover, which in the days before EGR, had no holes, and some exhaust gas went over one way or the other for carb heat. EGR came, and the powers that be tapped into it with an EGR valve for metered exhaust gas recirc at the first dark days of emission control. If the valve is there, cool. It either works, yay, or it's carbon blocked or frozen shut, and all that is fine. Or, there's a block off plate.
The only thing I'd be concerned with is if the EGR valve is WFO or gone and you didn't have the crossover blocked. Exhaust would come into the plenum, not the other way around.
