CFM and Carburetors:
Carburetors are rated by CFM (cubic feet per minute) capacity. 4V carburetors are rated at 1.5 inches (Hg) of pressure drop (manifold vacuum) and 2V carburetors at 3 inches (Hg). Rule: For maximum performance, select a carburetor that is rated higher than the engine CFM requirement. Use 110% to 130% higher on single-plane manifolds . Example: If the engine needs 590 CFM, select a carburetor rated in the range of 650 to 770 CFM for a single-plane manifold. A 750 would be right. An 850 probably would cause driveability problems at lower RPM. A 1050 probably would cause actual loss of HP below 4500 RPM. For dual-plane manifolds use 120% to 150 % higher.

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84 Camaro ZZ4 with HOT cam. 1.88 60' (12.98 @ 105MPH E.T.)
Recently Ported Heads, Installed Larger Race-Flo Valves, RPM Air Gap Intake, and 1 3/4" SLP Headers (No new times)
Other Mods: You name it and I have probably changed it.

2001 Dodge Ram Quad Cab 5.9L 4*2

The Bowtie
ASE Certified Auto Tech
LIVE AND DIE BY THE ALMIGHTY BOWTIE!

 

As much as I hate Edelcrock....yup thats about right.

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"American made baby. 100% American iron. The muscle among the masses. My hero. Yep, you can take your ergonomically designed, space age, computer controlled, 4 door, cup holding map lighted split double wishbone split fold down retractable cargo covered moon roof piece of transportation and keep it. For I have felt the thunder. And I know the difference!"
JSP Motorsports
ICON Motorsports

 

That's good stuff... doesn't mention bout dual planes though.. but i doubt it's a real significant difference.

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It's always SOMETHING

 

 

Think about the nature of the flow through the carb. If you had a single-plane manifold with a HUGE plenum, like 3-4 times the volume of a cylinder, then there would be enough volume in there to smooth out the poulsation of the flow that the engine creates as individual cylinders require filling. In a motor like that, the VE x RPM x CID equation would be accurate. But in fact, since no street manifold has such a volume as that, the carb does "see" the pulses from the engine; those pulses are considerably higher instantaneous flow than the above-described smooth flow would be. A dual-plane intake makes that effect even greater, since the pulses are farther apart in time, and have only half as much carb to pass through. Consequently the equation isn't quite as accurate for that situation.

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"So many Mustangs, so little time..."
ICON Motorsports

 

It agrees with my personal experience, too. That's why I tell people that just about any 350 will take a 750 CFM carb no problem.

 

I'm a newbie, does 4V mean four barrels?

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LUDICROUS SPEED GO!!!

 

I'm a newbie, does 4V mean four barrels?

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LUDICROUS SPEED GO!!!

 

Yes. "V" or "bbl" are variously used for "venturi" (not sure I'm spelling that right) and "barrel", respectively. "Venturi" is probably more technically correct, but "barrel" has stuck over the years.

Guess I should have gone for that 850 CFM q-jet RPM instead of the 1901 for the 396...

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82 Berlinetta, orig V-6 car, now w/86 LG4/TH700R4. 2.93 limited slip. Cat-back from '91 GTA, Accel HEI SuperCoil. AMSOIL syn lubes bumper-to-bumper. Daily driver, work-in-progress (LG4 w/'87 LB9 block, ZZ3 cam and intake, World 305 heads, Hooker headers & y-pipe, 3" Catco cat & 3" cat-back).
57 Bel Air, my 1st car. '66 396, 9.7 CR forged TRWs, Weiand Action+, Edelbrock 1901 Q-Jet, GK 270 cam, Magnum rockers, Jacobs Omnipack, 1-3/4" Hedders & 3" Warlocks, TH400 w/TCI Sat Night Special conv & Trans-Scat shift kit, MegaShifter, 3.08 8.2" 10-bolt w/Powertrax, AMSOIL syn lubes bumper-to-bumper. Idles smooth @ 600 RPM in D. Best 15.02/95.06 @ 5800' Bandimere (corrected 13.93/102.4 @ sea level).

 

Five7, that RPM Q-Jet is awesome!!! expensive though, but nice adjustability, especially the highway cruise circuit. worth the money.