***le pretty much says it. I've got a 290hp crate 350 in my Suburban. It's wearing a 600cfm Edelbrock carb, and I've got another Edelbrock AVS-style carb with the slightly smaller primary throttle blades, and the little larger secondary blades. Driving style aside, will the AVS-style carb get any better fuel economy on the highway, versus the AFB-style? Theoretically, it should take the same amount of fuel to run down the highway at a given rpm, right? -Brad
Hmmmm............Logic would say: smaller primaries, and no deeper "foot insertion", and you should come out ahead, on fuel consumption, with everything jetted properly............but honestly, as in what you said, "Driving style aside", I think there would be no noticeable difference. The later model carb is probably better all around, by virtue of the "more modern" engineering within.
bingo, I went from a regular Edelbrock AFB clone to the AVS and there is no difference mileage wise. Though it seems the AVS does seem to run a little better. Might be that I put a little more time into it, but still not perfect...
Isn't that essentially what Chrysler/Carter did with the Thermoquad? Went from the AFB style fuel delivery to the AVS style in 71? Or do I have it backwards? JK
Off the top of my head; AFB (Aluminum Four Barrel) counterweighted secondary air valve, came out around 1957. Replaced more complex to build, air flow limited, WCFB (Will Carter Four Barrel), larger air flow capable E series followed a couple of years later. AVS (Air Valve Secondary) adjustable by spring tension opening, vacuum operated secondary air valve, came out in sixties. Used OEM by both GM and Chrysler, but primarily Chrysler. Themoquad Plastic main body to control heat soak with m***ive sized Quadrajet style vacuum operated secondaries to make up air flow deficit of ultra small bore primary venturi used for low RPM efficiency. Higher air flow capability than either AFB, AVS, and even greater than 800 CFM Buick and Pontiac version of Quadrajet. Released OEM in 1971 model year on ChryCo cars, somewhat earlier for aftermarket.
Not much of a difference in fuel economy between the two,only way to improve highway mileage would be with rear gear ratio for highway cruising.
28-inch tall tires, 3.42 gears and .73:1 overdrive manual 4spd trans. I've done the big stuff, now I'm trying to dial in the little stuff. Looks like I'll be keeping the carb that's on it then (Edelbrock AFB-style), and replacing the C3B with a Performer (not a Performer RPM), and moving on from there. Thanks guys, -Brad
Imho, a no-brainer, install a good Q-Jet and then set the top rear ****erfly's so they kick in where you want them to. pdq67
I think you'll see more change going from old-school metering rods to newer ones with a bigger spread between power and cruise sections (or vice versa) than you will going between AFB and AVS. -Bill
Since the original question concerned clones; the following might be moot, but it does give a little insight into Carter 4 barrel carbs: http://www.thecarburetorshop.com/CarterFourBarrelCarburetors.htm Jon.
Sounds like you're on the right track. Nothing wrong with keeping the AFB style carburetor, but if you're not going to go with the RPM version of the Performer, you might reconsider giving the C3B the heave ho. Some say it outperforms the Performer, and the X version (C3BX) is on par with the Performer RPM. For comparison sake, Holley still makes a functional clone (300-36S) of the 67-69 Z28 manifold, long considered one of the better all around SBC four barrel intakes.
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