Ok guys I just scored this numbers intake and carb combo for an early 283. I cleaned up the intake and de dagged the ports The intake is mint and the carb had had a total rebuild and a recolour, I cleaned up the intake and gave it a squirt of paint, came put nice. Boring I know !! The real reason fopr the post is: can someone tell me what the cfm of the Rochester "4 Jet" carb is? Im thinking 500 cfm can anyone advise? Also, can anyone point me in the right direction as to a site where I can decode the numbers on this carb/intake combo? It should be dated b/w 57 - 62; I just need to confirm. Thanx, Rat
Thanks for the link but it is for Quadrajets.... This carb isnt a Spreadbore QJ, its a square bore Rochester stamped as "4 Jet" or in other words, a 4G with choke. Thanx Rat
These carbs flow more in the 400-450cfm range. Big Buick nailheads, Olds 371/394s, Cadillac 390s, and 340hp 409s had 4GCs with larger throttle plates and a bit more flow. There is a date code on the intake runner to the rear of the carb that will read something like C 26 3. C is the third letter, and so equals March. 26 is the day, and 3 is the year--in this case, 1963.
Thanx for the info Heathen, Ok the intake is a 64/65 Vette cast iron dual plane. Now still need to suss out the carb... I believe the 64/65 Vettes came out with the Carter WCFB carbs, not the Rochester 4GC.. I think my 4GC is circa 1957-62. I've looked all over the carb but cant see a number on it that would enable me to decode it? Should it have one? In any case, this intake should be running the Carter carb, not the Rochester !! By way of interest, anyone used this intake/carb combo an a mild, street driven 283? Rat
what are the casting numbers on this intake? most numbers also cross to the full size p***enger car plus the vettes on the low horsepower engines, 4 jets are so screwed up in thier iden***y ,unless you have the little triangle tag with the numbers on it application wise you cannot tell, you could pull the jets and see, there were 3 sizes of bores on these carbs, You can take it apart to check the jets and metering rods Rochester 4G/4GC Used on a variety of GM automobiles from 1952 to 1967, including the 1961 to 1963 Buick/Oldsmobile/Pontiac aluminum 215 V8's, the 4G was Rochester's first four barrel. Produced in 486, 553, and 692 CFM ratings, the 4G uses a squarebore layout with a conventional fixed jet, power valve and accelerator pump metering scheme. Secondaries are mechanically actuated but use an adjustable spring loaded air valve. Adjustment is achieved by loosening an allen head set screw and inserting a screwdriver. Rotating the screwdriver counterclockwise increases tension. The accelerator pump is also adjustable, using a link with 5 adjustment holes. Four center pivot floats are used. The 4G's used the small diameter 4-7/32" diameter air cleaner, shared by the first generation Carter AFB's, so the usual aftermarket air filter cases will not fit. However there are adapter rings and street rod sources usually carry compatible air filter cases. While the Rochester book mentioned in the reference section briefly covers the 4G, your best bet for information is a GM shop manual from the '50's or '60's. Model /CFM Venturi Diameter/ Bore Diameter primary secondary / primary secondary 4 Jet/ 486 1 1/8 1 1/4 / 1 7/16 1 7/16 4 Jet/ 553 1 1/8 1 15/32 / 1 7/16 1 11/16 4 Jet/ 692 1 1/8 1 15/32 / 1 9/16 1 11/16 If you can get an older copy of the Doug Roe book on Rochester Carburetors, it has a pretty good section on the 4G. jf If you need an air filter adapter for the 4G, the Mr.Gasket pn is 2082, to use a standard 5-1/8" filter base.<!-- / message --><!-- --><!-- edit note -->
Yes, the 250HP 327 Corvettes used WCFBs instead of the 4GC, but the intake manifold was the same, and as oldchevyseller said, a cast iron 4GC intake is a cast iron 4GC intake, be it Corvette, Impala, or your grandfather's C-10. Sometimes, the casting number listings get a bit creative. WCFBs can still be identified by casting numbers on the main parts when the I.D. tag is missing, but 4GCs have no such numbers. It's definitely not a '57-'58 carb; they had the choke housing up on the air horn. Someone has retrofitted an electric choke thermostat to your carb as well. From the look of the carb, it could very well be the same year as the manifold.
I always thought the Rochester flowed a bit more than the carter, ran a 4jet on my 283 Belair moredoor in high school, worked well on that mild motor. Then I built a 12 to 1 solid cam 283 with camel humps and a quadrajet, no comparison!
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