Carburetor for '69 300 with base 440

BamaFan

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Hello all. I fear my carb is probably shot from my engine fire last July.

I ultimately plan to make the motor dual exhaust with high-flow exhaust (can't fit headers on it unfortunately), but for now, I just want to get it running again.

In short, what is the biggest carburetor I can put on the stock manifold that won't spray in more fuel than the engine can handle; this would be be 350 hp K motor; and will also be enough when I do upgrade the exhaust? Basically, I don't want to buy a new carb again when I do get around to upgrading the exhaust probably next year.
 

CBODY67

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The stock carb was probably a Holley 4160 600cfm 4bbl carb. Adding dual exhausts ALONE will not need a larger carb. The 440/375 motors generally had a Carter AVS 750cfm 4bbl. carb. So, let THAT be the default "biggest carb" item.

The Holley has 1.56" throttle bores whereas the AVS has 1.69" throttle bores (4 of them the same size, as some AVS models had smaller primary sides).

Even with a dual exhaust, the 600-650cfm carb sizing will work pretty well. So no real need to go bigger than that. Some still prefer the 750, though, which can work too. Shop the sales and watch the prices over the next few months (Christmas time and all!!).

Back when the cars were new, Holley had the performance image with Carter AVS not far behind. I felt the metering on the Holleys was a bit better than the Carters, back then, BUT the Holleys had a notoriour reputation for needing yearly overhauls due to their gasket material back then. So many were swapped out for the AVS, as the AVS would not need that yearly maintenance.

In more recent times, I have bought new Holleys and they had no "yearlty maintenance" issues, but then too, the metering block and float bowl gaskets are now GLUED to the areas they physically touch. Not bad on the float bowls, but the meterinr block/plate gaskets are another story, from my own experiences. The Carter AVS has NONE of that, by observation. Plus you can alter the metering rods very easily, IF needed.

The current Edelbrock AVS2 can be a good choice, as can the Summit Racing 4bbls (built from an old Ford design), BOTH with annular discharge venturis. If you decide on a Holley 4160, then be sure to get the teflon (blue) accel pump diaphram installed so the chance of ethanol degrading the existing pump diaphram is less. Notice that the accel pump is at the bottom of the primary float bowl, for bulletproof re-filling of the pump, but IF the diaphram has a durability issue, it can drain the float bowl (slowly) onto the intake manifold and valley pan. I had a pump diaphram that got leaky on a Holley on one of my cars. Luckily, it was just a seep, so it caused no problem, but it MIGHT happen over time. Or perhaps I'm being a bit picky?

So, several choices! Watch the sales for the best pricing, too.

Enjoy!
CBODY67
 

Davea Lux

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For reliability and performance the 750 AVS is the way to go. You may need some linkage parts as well as the carb, those are readily available.

Dave
 

Turboomni

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Carburetor CFM Calculator - Find Your Carb Size

What Size Carburetor Do I Need?

https://www.inchcalculator.com/carburetor-size-calculator/

https://www.inchcalculator.com/carburetor-size-calculator/

Calculate the size of carburetor based on specific engine size and RPM

My stock 440 had a 1406 Edelbrock 600 cfm. I was shocked and thought it needed more. Found out that the 600 cfm was a restriction at well over 6000 rpm on a stock 440. I never went much over 5000. Didn't need a bigger carb. The correct sized carb will have good airflow over the the venturi's and a too large a carb will not. Around town driving and responsive throttle may suffer. Drag strip or only idle and WOT go big. Here are a few calculators to see for yourself.
 

saforwardlook

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Carburetor CFM Calculator - Find Your Carb Size

What Size Carburetor Do I Need?

https://www.inchcalculator.com/carburetor-size-calculator/

https://www.inchcalculator.com/carburetor-size-calculator/

Calculate the size of carburetor based on specific engine size and RPM

My stock 440 had a 1406 Edelbrock 600 cfm. I was shocked and thought it needed more. Found out that the 600 cfm was a restriction at well over 6000 rpm on a stock 440. I never went much over 5000. Didn't need a bigger carb. The correct sized carb will have good airflow over the the venturi's and a too large a carb will not. Around town driving and responsive throttle may suffer. Drag strip or only idle and WOT go big. Here are a few calculators to see for yourself.
I agree with the above as too large of a carburetor will diminish low end torque due to lower velocities of fuel/air through the intake manifold passages and into the engine.

Also, with regard to the original Holley's, their main problem was not necessarily poor gasket quality but rather poor cast metal strength that led to metering blocks warping and leaking air/fuel at very low mileage intervals that gaskets alone could not solve. Current model Holley's, however, are fine carburetors in terms of quality and do not have the original warping of metering blocks that plagued the original ones. Those were expensive carburetors to build and they had to compete in term of production price with the simpler more robust Carter offerings since Chrysler was very cost sensitive back in those days. So Holley had to cut quality to deliver a competitive cost to the Carters.

Carter carburetors in those early model years were not as good performers as the Holleys especially in around town driving where the throttle response was lagging compared to the Holleys. WOT throttle applications from rest often left the driver wanting as well with the Carters. But the Holleys only lasted about two years in normal use before needing to be replaced due to warpage of the metering blocks.

The new AVS II carburetors are good choices at reasonable cost but the current newer Holleys are also a great choice but incur a significantly higher price.
 
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1970FuryConv

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I put a 600 cfm Carter AFB on a 1973 440 New Yorker. Acceleration was poor after I got to about 40 mph.

I like the idea of a 750 cfm.
 

CBODY67

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I put a 600 cfm Carter AFB on a 1973 440 New Yorker. Acceleration was poor after I got to about 40 mph.

I like the idea of a 750 cfm.
The OEM AFB on my '67 Newport 383 4bbl has NO "velocity valve" in the secondaries. They are completely wide open above the secondary throttle plates. With that carb, the car ran very good. After I cleaned it up and dressed-down the casting flash on the venturi outer sides and such, then I could feel a very slight bog at WOT from idle. Never hesitated, just went and didn't stop until throttle setting was aimed toward "cruise".

Unfortunately, the way to get the velocity valves open sooner was to shave the counterweights, making them lighter.

Enjoy!
CBODY67
 

1970FuryConv

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The OEM AFB on my '67 Newport 383 4bbl has NO "velocity valve" in the secondaries. They are completely wide open above the secondary throttle plates. With that carb, the car ran very good. After I cleaned it up and dressed-down the casting flash on the venturi outer sides and such, then I could feel a very slight bog at WOT from idle. Never hesitated, just went and didn't stop until throttle setting was aimed toward "cruise".

Unfortunately, the way to get the velocity valves open sooner was to shave the counterweights, making them lighter.

Enjoy!
CBODY67
Hi Willis
I sold the car in 1998. Will keep your advice in mind, if I run into the same problem.
Chances of that: slim. :lol: Thanks anyway though, Ben
 

Turboomni

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No sign of BamaFan. Lets add to the confusion some more. Here ya go. At the end of the video he basically says the same thing ,the formulas will disappoint you on anything but a stock engine.

 
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CBODY67

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I suspect that the larger carb CAN increase the degree of "peppiness" in part-throttle response as the 750+ cfm square bore carbs usually have 1.69" primary throttle bores, rather than the smaller 1.56" (or even 1.44") primary throttle bores, as smaller cfm square bore 4bbls have. Less opening needed for a given cfm of airflow, by observation. For comparison, the 2bbls used on 383s had 1.56" throttle bores.

Other than the Holley 2300 2bbl, GM/Rochester built some 1.69" two barrels, starting in the later 1950s, even lots of Chevy 350 2bbls in the middle 1960s to middle-1970s were 1.69" carbs. Same base flange pattern as the Carter BBD 1.5 carbs, IIRC.

Enjoy!
CBODY67
 

fury fan

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My favorite carb on a stock non-HP 440 would be the 600-650 size Edelbrock. I was a big fan of the AFB version, the newer AVS version (which wasn't out when I bought carbs) will work OK, maybe a little better.

I have used a 750 Edelbrock AFB on a near-stock 350hp 440 and it absolutely sucked. (engine has alum intake, shorty headers, and 2-1/2" X-pipe exhaust - but standard 256deg cam).
After a year+ of fiddling with that carb, trying to tune it with the eye of a WB O2 gauge, I gave up.
Put on an Eddy 800EPS and it worked nicely right out of the box and got better with a week's worth of adjustment.

Some years afterward I read other horror stories on the Eddy 750 - one 'theory' I remember was speculation that when they made the molds they merely scaled it up from the 600, and that caused tuning issues.

I would love to see how a 600cfm SpeedDemon (a spreadbore Thermoquad type) would work, but I'm not interested in a $400 experiment right now.
 
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