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Since the base of the windshield is a low pressre area, and outside air is always cooler than underhood air, why did GM use a flapper valve that only opened at full throttle on cowl induction hoods?
Was it because in the weather moisture would enter and cause engine damage? I'm seriously thinking about the cake pan, foam cushion thing and appreciate any insight into this.

I ran mine without a flapper for years - had the carb / fuel freeze up one Winter on it - too much cold air is not a good thing. And yes it will suck water in - I watched drops run off the back of mine into the hole on more than one occassion. Not sure if that's why the made the flapper, bit those are good reasons to me.

Since you rarely drive your car in inclement weather and certain not in the winter really not much to worry about there pal. Besides a small amount of H2O shouldn't hurt anything....free water injection!! I am sure you fabricate it so there was a way to drain the moisture away as it comes in or make an additional insert you could drop in a the opening to create smaller opening up higher that minimal amounts of moisture could enter. You certainly won't need all of that air flow and horsepower when the roads are wet anyway!

Make the air pan and seal up to the hood and enjoy the added ponies! I have been thinking about doing one nascar style for mine just haven't gotten around to it yet.

Hey Don I'll be right there with you on this one. I just finally picked up a new cowl hood for my car at the swap meet last weekend. I'm in serious need get rid of the 1 1/2" drop base on the air cleaner. I picked up some bubble seal last fall at a swap to try and use as a seal. I had a web site saved for the cake pan because I couldn't find any heavy duty ones locally, but the link doesn't work now. I plan on just getting a screen to cover the rear of mine. Like Tom said how often to you drive in snow. And you may drive in the rain more than I do, but I think some of the screen kits out there would keep enough rain out even for you.

I wonder if the reason GM used the flapper valve was for cold drivablilty and emiissions. I don't know all of the science behind the heat riser and the stove that comes off the exhuast manifold but I'll bet they're pretty inefffective with a hole in the back of the hood gulping cold air. I'm not sure any of that matters to us anymore as very few of the cars with cowl hoods are still stock under the hood.

Hey Harley, if you don't sell that 1 1/2" drop base air cleaner base locally I'd be interested in buying it if it's for a Holley carburetor

David F.

David it actually started as a 3/4" drop base that I tweaked a little more. But if your still interested once I swap everything over you can have it for the cost of shipping.