phenolic vs wood carb spacer

Just pointing out that an aluminum spacer and an aluminum plate function in two entirely different ways. Aluminum is very good conductor of heat, which makes it a poor insulator if the goal of a spacer is thermal insulation as well as an increase in plenum volume.

Being that excellent conductor of heat, an aluminum plate acts partly as a radiator, drawing the heat out of the intake manifold and radiating it into the atmosphere, and partly as a shield blocking the heat radiated off the engine from reaching the carb.

I'll venture that most truly street engines won't respond favorably to an increase in plenum volume and that a spacer, even a 4 hole spacer, is a step in the wrong direction for them. A street/strip engine and/or a strip engine probably will respond favorably to a spacer.