4100 autolite for a 347 stroker

  • Interestingly 66 Thunderbirds with a 428 had 1.08 carburetors. I have a larger 4100 carburetor at home from the late 50's that is a 1.19.


    -Fred-

    65 Koupe early San Jose Phoenician Yellow 4 speed
    66 GT Koupe Dearborn Blue 4 speed
    66 KGT San Jose fastback pony interior Silver Frost 4 speed
    64 Falcon sedan delivery 289 4 speed
    65 Ranchero 289 4 speed
    66 Corvette roadster 427/425 4 speed

  • i know that 112 4100 carbs were install on 390 engines , i thinking a 112 4100 would run well on a 347 stroker , just looking for opinions ,thanks.

    Depends on a lot of factors.



    First understand that the assembly line Ford 4100As in the 1.12 size normally test as flowing around 526± a little SAE corrected standard cubic feet per minute (cfm). That is without an air cleaner, which is a restriction. 4100As can be reworked to increase air flow at standard rating conditions for 4V carburetors. The highest average corrected flows I use to see usually for modified units came in around 570± cfm corrected.



    Second understand that most dynamometer horse power does not automatically mean quickest car. Every car maker and aftermarket company and a few magazine companies proved many times it is best to have a carburetor a little too small than any amount too large. Many sources publish good rules for 4V carburetor sizing for specific applications where only one carburetor is used. The rules change completely for individual running induction systems as the physics / flow dynamics are very much different. Box ram type manifolds change the rules.



    289 c.i.d. engines that are seriously race prepared using a single 4V carburetor calculate out to working best with carburetor flows between 403 cfm and 569 cfm depending on the engine revolutions per minute (rpm) at maximum power, volumetric efficiency, and what that rpm at peak power is. Believe it or not some of the most successful 1960s-1970s racers using 289 c.i.d. engines in Falcons and Mustangs dropped from the 1.12 size carburetors to the 1.08 size carburetors.



    How about a 347 c.i.d. engine? The carburetor type and size I would recommend depends on lots of factors: type of vehicle, vehicle weight, transmission specifics, differential gearing, open or limited slip differential, camshaft characteristics (what was it designed to do?), specific intake manifold and any modifications thereof, exhaust system, type of fuel to be used most of the time, altitude the vehicle was going to be used around most of the time, and the type of driving use most of the time and occasionally.



    At or near sea level, assuming a Ford 4100 something (1.08, 1.12, or 1.19 size) based on the original post, one might choose a carburetor with an actual corrected flow between 483 and 683 c.f.m. covering street driving that won’t land one in jail to serious high engine rpm power band racing. As one goes up in altitude the size of the carburetor used would go down to stay optimum. Just because most Ford stock calibrations were rated for 0 to 5,000 feet above sea level doesn’t mean the air fuel curves stayed the same as altitude increased.



    Also don’t assume your vacuum secondaries are doing much if anything. Several problems can render them inactive. Your 500 cfm 4V might work as let us say a 300 cfm 2V. (I just repaired an early 1966 MUSTANG GT350 R-3259-1 Holley® carburetor that has not been a 4V unit in many years. Years ago somebody installed some incorrect parts (2) during an overhaul and the secondaries were dead from then on. I test carburetors before I dismantle them and most Ford 4100A secondaries do not function at all in as received condition.) It is very good practice to test secondary operation before saying you are done with a carburetor. You must set up a scenario where you can visually verify that the secondaries open at an appropriate time and an appropriate amount. Vacuum secondaries are self sizing in that for a given carburetor the secondaries that won’t ever open on lets says a 221 c.i.d. engine might start opening at 2,000 rpm on a 430 c.i.d. engine.

  • PS It is possible to take a "780" vacuum secondary carburetor and tune it (parts changes required) to work well on a 260 c.i.d. Ford industrial Engine in a Sunbeam Tiger or at the other end of the scale a 427 Light Weight or 427 HR race only engine in a 427 Cobra racer. There was a particular Ford carburetor that "size" that was specified and internationally registered as a racing option for Sunbeam Tigers, 1965 MUSTANG GT350s, and 427 Cobra full competition cars.

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