Blocking the heat crossover, IN the head.

Bad Sport said

I always was under the impression a cooler charge was a denser charge.

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A cooler charge means denser air, which increases the oxygen available for combustion. Hence intercoolers on turbos and all the cool air intake devices like hood scoops. But that does not change the amount of fuel by itself. The 0 HP increase test results from the dyno may well have been without the engine heat soaked and definitely not under a hood in a hot engine compartment, and so any HP increase due to denser air would not have been seen; it would only have checked the effect on exhaust flow.

But all that of has little meaning for the amount of fuel in the air; the optimum temps for good fuel vaporization and suspension works against air charge density so you're always balancing. Hence the hard cold start by the poster from CO with the Airgap. My son and I selected a Performer intake over the Airgap exactly so that it would warm up and run better in cool temps, even without the crossover. And thus all the exhaust manifold intake air heaters for air that you have seen on cars.

Modern fuels do have lower vapor temperatures so the need for a heat riser has decreased somewhat. If you only do fair weather driving, then you ought to get by with no crossover heat in most locations. But, I personally would not mess around with it beyond a good block plate. Easy enough to pull out later if you change your mind.