Is there a general rule of thumb for CFM Ratings with carburators vs. air cleaners? I have an Edelbrock 1405, I think it's a 650 CFM. I see air cleaner setups that range from 600 CFM to 1300 CFM. Was wondering if there was a general rule (like the air cleaner should be rated for twice the carb rating, or whatever)? Thoughts anyone?

hi , i have the same carb like you..i have the round style edelbrock air cleaner...no problem...

Yeah, I'm not having any issues either at the moment. But I wanted to change to something else - tired of the air cleaner assembly not sealing correctly on the carb because it hits the distributor. Bent it, cursed at it - still not a good fit. I also have to use a 1/2 inch plastic carb spacer (because I have the banjo fitting on the carb) that breaks, bends, etc. from the heat - which doesn't help the sealing issue either.

So I was looking at air boxes, carb hats, CIA's, and other methods for filtering air into the carb - thus the ? about CFM ratings - didn't want to put a 650 cfm carb hat on if it was going to be restrictive.

I'll use the '57 for reference, since I have a good bit of data on it.

I've been running a dual snorkel set-up on it that I tied to the stock vent inlets (above the headlights, ducts inside the fender to the engine compartment). I am confident the air cleaner would flow everything the vent ducts can feed it. Each vent duct is reported to flow 600 CFM - since I have a 750 CFM carb, I'm confident between the two of them they were providing adequate flow. For reference, I did some back-to-back runs switching between this system and open element (same size filter element), and the dual snorkel was consistently a tenth quicker than the open element.

In May I switched to a single duct "hat" fed from the panel beside the radiator. The duct/filter/hat are claimed by the manufacturer to flow 950 CFM. My ET's did not change when I went from the dual snorkel to the single duct hat system.

I went from a 1.6:1 (inlet flow to carb flow ratio) inlet system to a 1.27:1 inlet system with no apparent affect on ET or MPH. The effect of dual to single ducting, air inlets above the headlights to inlet on the front radiator panel, round air cleaner to hat; may be on top of the flow changes, and are undocumented by my data.

So the bottom line, is that you think as long as the inlet CFM is at least higher that the carb CFM, everything should be good? I wanted to think that as well, but thought I'd get an opinion from someone with more experience ( hail five7kid ).

As long as you don't introduce any restrictions or efficiency reductions such as air horn to lid clearance, tight elbows, etc.