It seems obvious that an open element would flow more air than the closed factory snorkel-type air filter assembly, but factory assemblies also duct "cold" air in from outside the engine compartment.

Has anyone ever done a comparison of some kind - such as back-to-back strip runs - to see what the actual difference is?

The thing is, it is OXYGEN that allows combustion, and the denser the air is, the more oxygen available to combust with fuel. Could a factory setup actually yield more oxygen through its cooler air supply?

I've never seen a factory air cleaner housing in a classic Chevelle (other than cowl induction or the old NASCAR ducted cowl induction) that ducted cold air to the carb. You could, of course, do it yourself.

I didn't realize they only came with open-element filters.

Snorkle types were the norm but they just drew air from under the hood. No ducting to outside air.

In the mid-towards-later 70's, we started seeing hoses attached to snorkel-type air cleaners to pick up "outside" air . You would also see vacuum operated flaps/pre-heat hose attached to air cleaner to pick up air coming over exhaust manifold when car was cold . This all goes under the heading of evolving emission controls .... Of course, any of the old ram-air or cowl-induction type set-ups picked up outside air ...

Y'know, I used to have a '67 which was stock and did not have the "cold air" snorkel duct, but I wasn't sure at what point Chevy started adding that feature. Thanks for the education!

I'm still wondering how much of a power loss an engine experiences from drawing heated air in through an open element air cleaner versus a closed system ducted from the outside. I guess I do a search on "ram air" and see what I find. Probably shoulda done that first.

Thanks, guys!

Try "cold air", too. Some people saw no change yet others saw a sizable gain. I guess it may depend on the temp difference between underhood temp and outside temp. Personally, I think it is an excellent idea. What stalls me from doing it is cutting up the original core support. Even getting air from a removed headlight requires cutting to make the opening big enough.

The ideal way, I think, is to get air from the cowl. It is a high pressure area and would be clean and cool. To do this you need to cut the firewall into the cowl area. Finding a good spot might be hard on a car with amenities like A/C, heater, and power brakes. I have, or had, I can't find it now, a picture of the NASCAR ducted cowl system. It's really neat. Sometime back someone sold a rather rough original for, IIRC, over $700. I didn't see where the auction finally ended.

The fender wells are another possible source. The main problem I see is mud and dirt being thrown into the inlet.