I "tested" the open air cleaner/closed theory the last few tanks of gas. Result? 0 difference in mileage, and seat of the pants. I used teh same filter, which is one of the TALL ones. I have yet to hear anything bad about Fram air filters, although knowing the history of their oil filters, it doesn't instill confidence.
Your carb can flow what? 800CFM max (depending on who made it) Until someone proves that the stock snorkel (basing this on my '81 up style radiator duct) can't flow that much air, or that my 350 NEEDS 800CFM, I'm gonna say it doesn't make any difference. Think about it. If the engine doesn't USE 750CFM, or even if it does, and the snorkel flows that much, an open element won't do squat for power, except hurt it, with warmer air. believe it was in the latest Petersons 4 wheel mag I got, every 10* raise of air temp=1hp. Ambient air temp is typically what, 80-90? Engine temp is 195, underhood temp crawling is likely 150, you are likely looking at 7hp loss through warm air. (total generalization there with numbers)
I would personally attribute all tested gains to either A)clogged, used filters or B) restrictive filters, which I believe is what K&N says is their advantage, easier flowing.
If you were to ask me, I'd say get the TALL air cleaner, run the snorkel, and if you want to spend money, buy the K&N, if not, stick with replacing a cheap chain store filter once it gets dirty.
Dorian
My tech/links page: <a target="_blank" href=http://www.dorianyeager.com/index2.html>http://www.dorianyeager.com/index2.html</a>
No anti-theft measures on your truck? No pity when its stolen