Reply to "In need of carb recommendations"

You didn't mention what intake manifold, if any, is currently available for your Pantera's engine. This makes a difference because the factory manifold was designed for a spread bore Autolite/Motorcraft carburetor known as the 4300D, whereas the aftermarket manifolds will be designed for Holley 4150 style carburetors. It appears the engine is equipped with an aftermarket manifold, because you are considering a Demon carburetor, but I don't want to "assume" anything.

The Autolite/Motorcraft 4300D carburetors were factory calibrated lean for emissions. Recalibrating the carbs for something close to 14.7:1 air-fuel ratio will improve the motors drivability, and increase horsepower by 10 to 25 bhp. But finding someone who can tune the 4300D carburetors in this day and age is difficult to do. A carburetor rated at about 600 cfm is fine for daily transportation purposes, but it will choke the 351C, especially the 4V version, at higher rpm. Ford used a carburetor of that size on the M code version of the 351C 4V specifically for the purpose of limiting the horsepower.

It is easy to warp the 4300D air horn (top casting) and once it is warped the fuel bowl will leak fuel dangerously. The 4300D is also known to cause the engine to stumble during high G-force cornering. For day in and day out driving and even moderate street-type performance it is just fine, but it is not suitable for the high G-forces encountered when cornering on race tires or on banked turns. Properly chosen aftermarket carburetors offer better fuel bowl designs and castings that don’t warp, they have features making them easier to tune, and they offer features such as annular booster venturis that enhance performance. These are some of the reasons people choose to replace the Autolite/Motorcraft 4300D carburetors rather than refurbish and re-use them.

The usual carburetor choices for a 351C 4V range in size from 750cfm to 850cfm. Some guys opt for a smaller 650 cfm carburetor because they believe it will improve low rpm drivability, or because they are influenced by the popular press & internet buzz which caters to the SBC and SBF style engines. My advice is to ignore everything you've read about SBC and SBF engines because a lot of it does not apply to a 351C with 4V cylinder heads.

Here are some carburetor recommendations from Sticky #3 of this forum (the engine forum):

(Note: If the budget is tight the Summit Racing carburetors are the lowest priced carburetors in the list)

Mechanical secondary/annular booster carburetors featuring street calibration and electric chokes

•Demon Carburetors #1282020 - 650 cfm - Speed Demon, mech. secondary, elec. choke kit #421440
•Demon Carburetors #1402020 - 750 cfm - Speed Demon, mech. secondary, elec. choke kit #421440
•Demon Carburetors #1563020 - 850 cfm - Speed Demon, mech. secondary, elec. choke kit #421440
•Holley #0-9379 - 750 cfm - Competition Series, mech. secondary, choke horn equipped
•Holley #0-9380 – 850 cfm - Competition Series, mech. secondary, choke horn equipped
•Quick Fuel Technologies (QFT) #SS-650-AN – 650 cfm – SS Series, mech. secondary, electric choke
•Quick Fuel Technologies (QFT) #SS-750-AN – 750 cfm – SS Series, mech. secondary, electric choke

Vacuum secondary/ annular booster carburetors featuring street calibration and electric chokes

•Demon Carburetors #1282020VE - 650 cfm - Speed Demon, vac. secondary, electric choke
•Demon Carburetors #1402020VE - 750 cfm - Speed Demon, vac. secondary, electric choke
•Demon Carburetors #1563020VE - 850 cfm - Speed Demon, vac. secondary, electric choke
•Summit Racing #M08600VS - 600 cfm – vac. secondary, electric choke
•Summit Racing #M08750VS - 750 cfm – vac. secondary, electric choke

Vacuum secondary/down-leg booster carburetors featuring street calibration and electric chokes

•Quick Fuel Technologies (QFT) #SS-680-VS - 680 cfm – SS Series, vac. secondary, electric choke
•Quick Fuel Technologies (QFT) #SS-735-VS - 735 cfm – SS Series, vac. secondary, electric choke
•Quick Fuel Technologies (QFT) #SS-780-VS - 780 cfm – SS Series, vac. secondary, electric choke

Annular booster venturis atomize fuel better and provide a stronger fuel metering signal at low air velocity. In other words, annular booster venturis benefit the low rpm and mid-rpm performance of a motor in the same manner as the smaller primary throttle bores of a spread bore carburetor. These attributes make annular booster venturis popular for improving the low rpm operation of performance engines, where they have earned a reputation for improving torque, horsepower and throttle response at low engine speeds. However the improvement in fuel atomization distributes fuel more consistently throughout an intake manifold, resulting in more consistent fuel/air ratio from cylinder to cylinder, therefore annular booster venturis actually improve torque and horsepower across a motor's entire power band; and they improve fuel economy too! The only drawbacks of annular booster venturis include their larger physical size (which reduces the airflow capability of a carburetor by a relatively small amount) and their greater cost of manufacture.

-G