Editing Intake manifold (section)
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===Air gap=== [[File:Rpm 7501 air-gap.jpg|thumb|400px|left|Edelbrock SBC RPM Air-Gap intake. Air can circulate beneath the plenum; plenum is separated from the hot motor oil being splashed onto the bottom of the intake where it seals the lifter valley.]] The so-called "air gap" intake concept has been around since the late '40s-early '50s. It has been used by various auto makers through the years, like Pontiac, as original equipment. Air can circulate beneath the plenum; the plenum is separated from the hot motor oil being splashed onto the bottom of the intake where it seals the lifter valley. Only because the Chevy V8 uses the intake bottom to seal the lifter valley is this considered to be an improvement. Other engine that use a separate plate to cover the lifter valley have had "air gap" intakes all along. But with the SBC engine, especially if using Vortec or aftermarket heads that lack a heat crossover beneath the plenum, the engine may tend to be cold-blooded until the intake comes up to temperature from engine heat. That means the Edelbrock Air-Gap intake will require a longer warm-up. In cold weather this can lead to drivability problems, almost like a tunnel ram. The air/fuel mixture- if tuned for a fully warmed up engine- will be lean until the engine is up to temp. This can be compensated for by the choke, but if using the choke, spirited driving is out until the choke is fully open. <br style="clear:both"/> As far as cutting the RPM like the AG, because the carb height and runners are basically the same between the two intakes, that mod will make their top end output equal for all intents and purposes. Not saying that's the thing to do in every case- just saying that ''if'' the same powerband as the AG is wanted, it can be had by notching the divider. For the right engine and vehicle combo (low gears, higher stall speed, light weight, more track than street, etc.) notching the plenum (or adding an open spacer) can help more than it hurts.
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