Is this carb correct ?

Tim_Fury

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So, I have a 1965 sport fury with a 383 four barrel, 4 speed car.
I just took the carb off to rebuild it. it is a Carter AFB 4131s which when i look it up is a 575 cfm carb. My question is on these 383 cars didn't they have 750 cfm carbs ? is this carb correct for this car ? I also thought that these engines had dual point distributors but this car has a standard mopar single point dist. please advise

Tim
ps: another interesting fact is the car has a dea agent sticker on the windshield and its black. wondering if some of these cars were bought by us gov't agencies ? fender tag verifies 383 4 barrel , 4 speed
 
The carb shows up as a 66 auto 383

The Drug Enforcement Administration was established on July 1, 1973


Alan
 
Looking at the 65 parts book there are four different carbs listed for the 383 manual, not sure why the differences.
3849s
3855s
3859s
4125s


Alan
 
Your car should have a 4125S Carter ABS for 65 383 w/four speed in a C body. 4131 is for 66 C body with automatic.

Correct CFM is 625 (or 650 I think). Single point distributor, with specific manual trans curve. @halifaxhops should have the correct distributor for your car.
 
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My question is on these 383 cars didn't they have 750 cfm carbs ? is this carb correct for this car ?

If you check with one of the MANY carb-sizing websites out there, you'll see that if you assume a max rpm of 5200, a 500 cfm unit is all you need.
CFM Calculator
https://www.inchcalculator.com/carburetor-size-calculator/

And this is a good read: CARB SIZE MATTERS: What size carburetor do I need?

I use a 625 cfm Street Demon on my 30-over, U-code 440, mildly ported, Eddy Performer 440 intake, Hooker headers mill, with WOT upshifts at about 5100-5200. Fantastic throttle response, and it's all the carb a heavy street car could ever use.
 
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So, I have a 1965 sport fury with a 383 four barrel, 4 speed car.
I just took the carb off to rebuild it. it is a Carter AFB 4131s which when i look it up is a 575 cfm carb. My question is on these 383 cars didn't they have 750 cfm carbs ? is this carb correct for this car ? I also thought that these engines had dual point distributors but this car has a standard mopar single point dist. please advise

Tim
ps: another interesting fact is the car has a dea agent sticker on the windshield and its black. wondering if some of these cars were bought by us gov't agencies ? fender tag verifies 383 4 barrel , 4 speed
I'd be interested in buying that carb from you, if you decide to sell it.
 
If the carb was ever replaced, it might well be that the superceded part would be what is on the car, as the orig carb would have been "out of production" at that point in time.

One reason that you saw many OEM HP engines of small displacement have 780cfm carbs on them is that what was on them from the factory had to be used in the stock classes they were raced in, even if it was way too big. As in the Camaro Z/28 302 with a Holley 780cfm carb.

Think of carb cfm flow ratings in the same orientation as the fuel flow ratings of fuel injectors. More horsepower needs more fuel flow, less horsepower needs less, similarly. More is not always better, past a certain point. On the Holley 4bbls, no matter how much total air flow they might pass, the secondaries will only open enough for what is needed, being modulated by air flow through the carb, provided the correct spring is in the secondaries vacuum diaphragm mechanism.

A factory single-point distributor, with a good set of points in it, will usually perform just as well as a dual-point unit, in all but higher-rpm use. Without the trouble of getting the two sets of points set correctly. Back in the later 1950s, when higher-rpm camshafts and multiple carbs came into use, many engines so-equipped came with factory dual point distributors to better fire the mixture at the higher rpms . . . with the possibly weaker distributor coils of that time frame.

For 1965 parts and service manuals, www.jholst.net has those for quick downloads. LOTS of information there, especially for 300 Letter Cars.

Enjoy!
CBODY67
 
FWIW, IIRC, Holley rated their 4bbl carbs @ 1.5 Hg, 2bbl @ 3.0 Hg, Chrysler used their own system rated @ 2.0Hg, so any factory Chrysler ratings you find aren't quite comparable to what we regard as the norms. As long as the carb has positive CFM control, vacuum or air valve you can use most any CFM you want without too much downside, witness Pontiac's sprint six banger, 230 CI (later 250 CI)with a 750 CFM Quadrajet.

I believe your intake manifold has smaller intake holes so you have to be careful retrofitting a later carburetor that probably has 1 11/16" throttle blades and a larger air horn requiring a different air cleaner, if you're considering that avenue.
 
The original HP Books "Holley Carburetor" book did state that 4bbls were 1.5" Hg and 2bbls were 3.0"Hg flow rates. I suspect this was due to the flow benches of that time only having a certain amount of capability of pulling a vacuum?

Before "cfm", the ratings were done with "Venturi area", with more being better. But only the biggest carbs back then, using their throttle bore sizing to compare to later cfm-rated carburetors, were probably in the 600cfm range, I suspect. With some of the later '50s 4bbls probably being closer to 450cfm?

In the "Rochester Carburetor" book (by S-A Designs, I believe), it was noted that although the throttle bore and primary venture sizes of the QuadraJet 4bbl had remained the same all the way in to the smog-engine 1980s on 5.0L V-8s, they didn't flow 750cfm as the original 1967ZJets did. Not from secondary air valve spring tension, but from the tab on the air valve shaft being taller than the original tab was, which didn't let the air valve open to full-vertical, resulting in only about 650cfm flow.

Even on the stock 350s back then, if the air valve spring tension was not high enough, the air valve would open too soon at WOT, with the resulting "QuadraBOG" situation. Too much air at too low of an rpm for best performance.

Back when the Pontiac OHC 230 6-cyl was out, we knew the QJ was probably too big for that size of engine, but figured that Pontiac had it re-calibrated for that small of an engine size. The carb's actual cfm was not mentioned, as I recall. But this was also GM's only modern 4bbl at the time, so it was the default choice. At the time, the idea of a HP 6-cyl engine was a bit "European" for many USA car buyers, with big and bigger V-8s being the primary choice, when available. In retrospect, there probably had to be some non-defeatable design attributes to get that carb to work on that small engine. What they might be could be a mystery, at this point in time, as I don't recall any real mention of them back when the cars were new.

On the other hand, the original Holley 1850, which was OEM on Ford-Edsel-Mercury-Lincoln V-8s in 1958, at 600cfm, went from the small (original FE) 332 to the Lincoln 430 V-8. Same Holley part number, same jets and such (listed in the Holley Variable Spec Manual). BTAIM

Enjoy!
CBODY67
 
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