the reason you picked up by removing the outside air source ment your engine was jetted to lean...by removing the outside air you richened it up, with jetting dialed in with out air you will make more power....if you can benifit from it...tires....Rob
The car is no way lean the problem was the restriction of air flow thru the factory air cleaner assembly. Not much heat around the engine because everything was cooled between passes. I do my plug test on all my engines. Every racer no's that a engine on the verge of leanness will run faster but you take the chance of melt down. You never herd the old saying " LEANNER IS MEANNER "
The flapper hood is way cool and a good selling point on any Chevelle.