Atmospheric pressure decreases with increasing altitude.

I'm not here to bring a negative light to the subject but given the airflow "tech" that's being discussed.....which is all good, we are driving street cars here.
IMO a few horsepower lost over the type of air filter used is really not that significant.
16 years ago when I first developed the WFO, I did track testing with open element housing and the WFO shaker setup, swapping out with a standard paper and a cotton gauze filters. The performance between the two was virtually the same.

I think one of the differences now is what is a street car. With many builds approaching or beyond 600hp on the street one must have adequate and proper air flow. I'd say the biggest limiting factor many have is just hood clearance..It either affects engine tuning affecting use of carb spacers or higher intakes, or reducing air filter size or ultimately reducing proper function of the air filter assembly.

Nothing wrong with experimenting with a street car. We all like to go fast and air cleaner setups are the cheapest/easiest/fastest thing you can change at the track and perform actual back to back testing. As already mentioned there can be some significant gains with just air cleaners. Some are just absolutely horrendous.

So here is A-B-A with the air cleaner base (only) pictured without, with, then without again. Red is with the base installed. Hard to believe it lost 40+ hp with this base but this Qjet was finicky, it hated the airflow turbine equally as bad. A smooth radius a/c base, like OEM was perfectly fine.https://uploads.tapatalk-cdn.com/202...6eaa6b37b5.jpghttps://uploads.tapatalk-cdn.com/202...0340869dd7.jpghttps://uploads.tapatalk-cdn.com/202...538bd5603e.jpg

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What exactly were the tests?

Dyno tests on a 902, setup is in the 3rd pic (hard to see). The only difference in 25 and 26 was the addition of the air cleaner base. For test 27, it was a different day, ac base was removed, and a 1" spacer instead of a 1/2" spacer was also added, but there is very little difference with it and 25, so i feel it's a valid A B A.

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Mchell, great post! I also love real world no BS info like you have provided!

Another question here... Has anyone tested single vs dual snorkel units, or different size snorkels? I'd like to try an OEM air cleaner like mchell but the original dual snorkels are pricey and single snorkels are near free! Wondering if/how much difference there is with a single snorkel vs dual or position of snorkels? I have been running no air cleaner at the dragstrip as I hate my current air cleaner setup! :eek: This post has motivated another winter upgrade!

That's something I'm going to play with shortly. Chevrolet cowl induction setups use a single snorkel air cleaner sealed to the hood. So when the cowl induction is closed (anytime the throttle isn't floored) the engine breathes through that single snorkel only.
I have 2 cars this way (Chevelle and Z/28) I'm going to modify the chevelle, taking another single snorkel cowl induction air cleaner, combine the two and make a dual snorkel so it all looks factory. Not that I think it will do much other than look cool and make people wonder. Since I need to modify the height of the seal anyway for the new setup I figured I may as well make something unique.

Performance wise it won't do anything because at full throttle the hood is open ingesting outside air anyway.

If you have a sealed up air cleaner ingesting hot engine heat under the hood, it would be easy to test the theory though. But most guys have already found that even if you have a single snorkle large diameter air cleaner (or a dual), they run better if you remove the large 16" lid and just put a smaller 14" lid on it, affectively making the air cleaner an open element setup and using the base to insulate the filter somewhat from engine heat. The OP found this to be his best setup to date if you're stuck ingesting engine heat.

Dual snorkel vs. open aircleaner.
 

My engine is a 455+040.
750 Q-jet, iron intake with 0.5" spacer and mild Crower HFT cam.
On a DynoDynamics chassidyno and the hood open, the engine gain 20hp switching the Dual Snorkel with 14"*2" filter to 14"*3" open filter with flat base.

The best pull was 417hp with 14"*3" open filter.

All pulls was made with open hood so in the streets it may be different.

From S.F. in Sweden.

Not surprising!
You might just pick up even more power if you remove the 1/2” carb spacer and find a 14” base that has radius leading into the carbs inlet instead of running just a flat base.

Four flow test that I did when I first got my flow bench to help out a dirt track guy with his 2 bbl Carb reflected test I posted up here done by Divid Vizard exactly!

Here’s the last one.