The truck in my avatar has a 351W and I am setting up a two barrel carb to be able to swop out fairly quickly with the current four barrel, looking for a bit more economy on long trips. I've never much cared for the big pancake type air filters and I'm looking to fit something a little better looking. Besides the dramatic cost of importing anything due to our exchange rate, I want to go with something where I can get replacement elements fairly easily. I have an old Valiant housing which will take an element (about 8" diameter, 2.5" tall) that is freely available here. I can make it fit quite easily. Views seem to be mixed on going too small though, some saying that it will clog up much quicker and subsequently hurt economy? Looking for opinions on this...
You will probably get worse mileage swapping to a two barrel that has primaries close to 1/3 larger than your present 4 barrel when most of your driving is on the primaries unless you have a heavy foot,the larger the air filter diameter the more air flow that 8" is not going to cut it if your goal is more economy.You are going in the wrong direction with both your ideas.
If you want a 4bbl and fuel economy, go with a spread-bore carb. Think Q-Jet or Holley spreadbore with vac secondaries. The Edelbrock/Carter 600 CFM does well in terms of MPG, too.
I'll add too, if you go with a Holley with vacuum secondaries, you could stick a heavy spring behind the vac secondary diaphragm so it won't open the secondaries too much.
i remember back in high school, we would stack two elements on top of one another, for more air flow. just need to make the stud longer.
I won't get into the 2bbl vs 4bbl fuel mileage argument. As for air cleaners, efficiency is determined by the area of flow which is a factor of both diameter and height PLUS the restriction and efficiency of the paper media. Air cleaner restriction is measured in inches of water. You can buy "filter minders" at truck dealerships and suppliers for the diesel road truck market. You can get the simple flag style which will trip and latch to show red when the filter needs changing or you can get the type that has a scale and ratcheting movement to lock in at the maximum restriction experienced, typically scaled like 5", 10", 15", 20" and max at 25" H20. Naturally you need a low profile fitting installed in the air cleaner lid and a small hose or line run to whereever you wish to mount the indicator. It can be mounted direct but will stick up appx 2". An alternative would be a dash mounted guage which reads inches of water.
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