The Carburetor Shop LLC
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Street Eldon, Missouri 65026 Home | History | F.A.Q. | Orders | Contact Us | SELL TO US Carburetors | Repair Kits | Other Parts | Literature | Tools | Articles | Troubleshooting | Carburetor Identification Passenger Kits | Truck Kits | Tractor Kits | Industrial Kits | Marine Kits | Multi-carb set-ups Car Comics | Car Records | Stamps and Coins | Car Trading Cards | Subscription Cards | Oakland and Pontiac OK, so I misled you with the title, sorry. To my knowledge (and what is available in existing Carter drawings), Carter published CFM for only a few AFB carburetors, these are listed below. When the AFB was produced, the method of comparing carburetor air flow was total venturii area. The first Competition Series catalogs published by Carter still listed total venturii area, while adding CFM ratings. There is no doubt that if CFM figures were published by engineers, they would be a more accurate measurement than total venturii area. But engineers test for CFM, and marketing personnel assign the published rated numbers. Anyone that thinks the engineers built carburetors to produce exactly "nice" CFM ratings such as 500 or 525 probably still believes in the tooth fairy! As an example, Carter flowed the AFB 3636s which produced 1128 CFM at 3 inches of Mercury, and 939 CFM at 1 1/2 inches of Mercury. I have gone through the existing Carter drawings (I am the current caretaker) and calculated total venturii area for each one for which I have data. There are other AFB carbs for which I do not have venturii data. Carter published TFN's [(T)emporary (F)ield (N)otice] pages on very low production carburetors, until there was sufficient demand to print catalog pages. Unfortunately, there are some for which catalog pages were never printed. I have the TFN's which list a bill of material, but do not give venturii data. For those that think about rebuilding kits, and tuning parts; I can assure you that, as of this writing, rebuilding kits with LEATHER accelerator pumps, main jets from 0.050 to 0.120 inch, original metering rods, custom metering rods, and different calibration vacuum springs are available for ALL of these carburetors. So, listing by carburetor identification number within total venturii area (note the "s" suffix is omitted): Area of 3.56 square inches: 2441, 3759, 3892 Area of 3.76 square inches: 2798, 2799, 3258, 3259 Area of 4.02 square inches: 4061, 4344 Area of 4.2 square inches: 2640 Area of 4.24 square inches: 2652, 2653, 2790, 2791, 2948, 3083, 3393, 3394, 3564, 3980, 4119, 4120, 4121, 4122, 4294, 4295, 4304, 4305 Area of 4.44 square inches: 2448, 2641, 2642, 2650, 2651, 2686, 2744, 2773, 2787, 2801, 2805, 2806, 2812, 2813, 2823, 2836, 2855, 2856, 2925, 2969, 2970, 2991, 3103, 3105, 3106, 3131, 3140, 3213, 3247, 3249, 3252, 3253, 3257, 3826, 3827, 3853, 3854, 4055, 4056, 4298, 4331, 4332 Area of 4.68 square inches: 2859, 4758, 4761, 9500, 9501, 9510, 9511 Area of 4.92 square inches: 2794, 2797, 2854, 2927, 2950, 2968, 3108, 3133, 3134, 3152, 3214, 3251, 3254, 3256, 3374, 3375, 3392, 3478, 3543, 3611, 3612, 3613, 3614, 3615, 3644, 3855, 3856, 3858, 3859, 3860, 3871, 4130, 4131, 4200, 4299, 4476 Area of 5.62 square inches: 3726, 3540, 3808, 4059, 4060, 4132, 4133, 4136, 4137, 4138, 4250, 4258, 4309, 4310, 4311, 4352, 4353, 4467, 4622, 4660, 6043, 6045 Area of 6.06 square inches: 2479, 2480, 2506, 2696, 2697, 2740, 2751, 2767, 2768, 2802, 2814, 2815, 2819, 2820, 2840, 2853, 2862, 2863, 2903, 2906, 2951, 2952, 2975, 2976, 2981, 2982, 2992, 3041, 3088, 3089, 3116, 3123, 3124, 3125, 3177, 3178, 3204, 3285, 3297, 3300, 3314, 3326, 3351, 3352, 3354, 3437, 3438, 3447, 3452, 3477, 3479, 3480, 3481, 3502, 3503, 3505, 3521, 3522, 3523, 3524, 3545, 3574, 3578, 3579, 3633, 3634, 3635, 3645, 3646, 3647, 3648, 3649, 3650, 3651, 3655, 3656, 3665, 3686, 3687, 3725, 3887, 3895, 3896, 3898, 3899, 3900, 3903, 3904, 3905, 3921, 3922, 3923, 3924, 3925, 3928, 3929, 3930, 3931, 4030, 4031, 4033, 4034, 4035, 4036, 4037, 4041, 4053, 4054, 4139, 4140, 4147, 4148, 4168, 4169, 4170, 4171, 4179, 4180, 4181, 4204, 4205, 4216, 4242, 4243, 4244, 4245, 4246, 4248, 4312, 4324, 4325, 4328, 4329, 4343, 4354, 4355, 4358, 4360, 4361, 4362, 4363, 4393, 4402, 4413, 4430, 4431, 4432, 4453, 4468, 4469, 4562, 4563, 4583, 4584, 4585, 4619, 4620, 4621, 4623, 4624, 4661, 4662, 4663, 4664, 4665, 4692, 4699, 4759, 6044, 6046, 9625, 9626, 9627, 9635, 9636, 9637 Area of 6.3 square inches: 2507, 2800, 2877, 2897, 2955, 3010, 3012, 3221, 3266, 3269, 3298, 3310, 3361, 3362, 3433, 3435, 3460, 3461, 3720, 3721, 3804, 3810, 3811 Area of 6.7 square inches: 3270, 3345, 3444, 3499, 3783 Area of 7.08 square inches: 3443, 3593, 3596, 3705, 3861, 4326, 4327, 4345, 4346, 4760, 4762 For reference: I have compared total venturi area against published CFM
ratings of the few carbs that were published, and a figure of 107 CFM/In2 These figures would be a maximum castings rating. Carter occasionally used deflectors or restrictors to modify the air flow. A good example of this is the "dummy" hot idle compensator requested by Pontiac on the standard transmission GTO's so the four-barrel engine would not outrun the more expensive tripower engine. So if one wishes to come up with an APPROXIMATION that is probably better than most internet guesses, one may multiply the venturi area listed above by 107 to come up with a figure. Carter published CFM ratings for the following AF.B's 400: 9400, 9410 500: 4758, 4761, 9500, 9501, 9510, 9511 570: 4742, 4745, 4746, 4969, 4970, 4971 575: 3721, 6310, 6478 590: 3804 610: 3361 625: 3783, 4759, 9625, 9626, 9627, 9635, 9636, 9637 700: 6212 735: 6130 750: 3705, 3861, 4760, 4762 939: 3636 As with all of the articles on our website, the reader may copy and redistribute this article. We ask only that credit for the original article is given to The Carburetor Shop |