Thread: CFM vs CID

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just thinking out loud.

Discounting mounting flange, would a v8 carb run on a 4 cylinder if the secondaries were disabled?

Technically yes, but a proper sized 2 barrel would be more efficient.

After the first "gas shortage" hit, a very popular "trick" for those guys with quadrajet ( quadrabogs) carbs was to replace the base gasket with a homemade one that only had holes for the small primary venturies. This "trick" resurfaced afew years back when guys were mounting dual quad setups but the rear carb was setup as a dummy by doing the same thing, a full gasket with no openings - so no airflow.

big fe fords came with 2 bl carbs . but then some of them 2 bls were huge.
my favorite set up is to space the small carb up 2in lean them out and increase the port Velocify.

I'm my shop somewhere should be a quadrojet dualjet. They only made them for a year or two. It's a Rochester quatrojet without any machining in the secondaries, and the top cover blocks them off.

“…..just thinking out loud.

Discounting mounting flange, would a v8 carb run on a 4 cylinder if the secondaries were disabled?......”



Sure. The key is sizing and jetting. You want something with the smallest throttle plates you can find and then jet it according to the to the engine needs. When I put the 74 Mustang with a 2.3 together for the wife, I put on a 302 Motorcraft 2 BBL. The throttle plates were way bigger than I wanted but it was what I had on hand. Ran good with an automatic and later with a 4 speed when Cade inherited it. The car is still using that carburetor.


As far as disabling the secondaries I don’t know that I’d bother as long as the secondaries are vacuum (Holley) or it has an air valve over the secondaries (Carter AFB/AVS or Quadrajet). These carbs will only start passing fuel/air mixture if the engine demand is sufficient to require it.

In the early sixties the factory put 4 barrel carbs on a few of the Pontiac 4 Cylinders and I think (but not sure) it was also available on the Chevrolet 4 cylinder Nova engines. Now as I recall it was an AFB only rated at around 450 CFM, but still.

Quote from Wikipedia



“…..The Trophy 4 engine is a short-stroke, 45-degree inclined inline four created from the right bank of the 389 V8 for the debut of the Tempest in 1961. Its 194.43 cu in (3.2 L) displacement is precisely half of the 389, with an identical bore and stroke of 4+1⁄16 in × 3+3⁄4 in (103.2 mm × 95.3 mm). It shared most of the 389's tooling and up to 120 of its parts. This degree of commonality enabled it to be produced on the same lines as the V8, allowing substantial cost savings. The Trophy 4 weighs about 470 lb (210 kg), as compared to the 650 lb (290 kg) V8 it was based on……..A "power pack" option for the 1962 four-barrel carburetor increased rated power to 166 hp (124 kW)…..”

If you already have the carb throw it on and give it a try.



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