Reply to "New Carb recommendation"

My usual recommendation usually includes a dual plane intake manifold, which you already have. The manifold’s plenum divider should not be cut down. The goal is to broaden the time between pulses in the intake system thus improving mid-range power over a wide range of engine speed. There is quite a bit of horsepower to be gained by blocking the manifold’s exhaust heat passage, but this is not recommended for folks living in colder climates.

Select a carburetor having annular booster venturis, having vacuum secondaries, having an electric choke, and calibrated for "street performance". Or better yet, calibrated for your particular application by a carburetor tuner business.

In terms of size, some owners opt for a 600 to 650 cfm carburetor. Carburetors of that size will fit on an unmodified 1970/1971 iron intake manifold (D0AE-L casting number). The 351C 4V engine of 1970/1971 was equipped with a 630 cfm Autolite carburetor (model 4300A). The “smaller” carburetor is probably the best choice for a single plane Edelbrock Torker intake manifold as well. I mention this because the Torker has been a surprisingly common choice for an intake manifold. Check out these 600/650 cfm carburetors:

600 cfm, vacuum secondary, low budget: Summit Racing #M08600VS
650 cfm, vacuum secondary, better budget: Demon Carburetors #1282020VE
650 cfm, mechanical secondary: Quick Fuel Technologies #SS-650-AN

However, in terms of selecting a carburetor for a dual plane manifold with a full height plenum divider a smaller carburetor offers no better low rpm performance than a properly calibrated carburetor of larger capacity. If the engine is equipped with a dual plane manifold (full height plenum divider) its performance at higher rpm will be impacted by a 600/650 cfm carburetor. Therefore if you want the Cleveland to perform as it is capable of performing, over a wide power band encompassing idle to 7000 rpm, and to produce maximum power at 6000 rpm, then opt for a 750 cfm version. The 351 Cobra Jet engine (Q code) was equipped with a 750 cfm Motorcraft carburetor (model 4300D).

A 750cfm carburetor has 1-11/16" throttle blades and 1-3/8" venturi throats. Carburetor jetting should be approximately #68 to #70 primary jets, and approximately #80 secondary jets. There are very few choices if you limit the selection to those having annular booster venturis, an "electric choke mechanism", and "vacuum secondaries". Check out these vacuum secondary 750 cfm carburetors:

750 cfm, low budget: Summit Racing #M08750VS
750 cfm, better budget: Demon Carburetors #1402020VE

If your preference is a mechanical secondary (aka double pumper) carburetor, check out these 750 cfm versions:

Quick Fuel Technologies #SS-750-AN
Holley #9379
Demon Carburetors #1402020

The Holley and Demon mechanical secondary carburetors do not come with electric chokes, but an electric choke can be added to either of them.