I have a 65 Valiant rebuilt stock 273 2bbl motor It has a 4speed dual exhaust 81/4 sure grip with 373s I was thinking of adding a 4bbl but I also have a brand new 500cfm Holley 2 bbl,was wondering what the difference would be between a small 4 bbl 600 cfm or the 500 cfm 2 bbl
Thanks

Finding a 4bbl manifold that has ports matching the 273 intake port will be a challenge. A 4bbl will provide better lowend torque, throttle response and better mileage. You would also have a port matching issue with the 500 cfm carb with the stock manifold. You would have to mill the ports for the butterflys to open.

600 double pumper is the way togo

I would not go with a double pumper. With a stock engine I would say a 650 with vacuum secondaries.

Cam is a big factor here.


In reality, it is the biggest factor in power, throttle response etc..

BUT that said, a small 4 bbl will be easier to tune,a nd easier on fuel. Probalby no difference in all out performance.

IMHO 600 is still too large for a stock 273 2 bbl motor. Holley makes 4bbl's into the 300's. 500 or so is plenty for that.

a stock 273 4bbl intake is pretty decent for a stockish 273 and the 500 eddy is probably going to work the best for a stockish 273.

Just an FYI the holley 2bbl will fit on a 360 2bbl manifold and the manifold can fit the 273 heads with a little grindinng of the bolt holes and port mis match is not too bad as the 2bbl manifolds have slightly smaller ports than a 4bbl manifold, but if it was me I would find a factory 273 4bbl manifold and run a small 4bbl.

I agree with the others that would go small 4 barrel vs big 2 barrel. Form my understanding the big 2 barrels were developed for racing classes that REQUIRE a 2V. and are almost always operated at or near WOT. Part throttle reponse sucks compared to a 4V with their much smaller primarys.

The 4bbl progressively dumps in the air and fuel compared to the 2bbl that pretty much dumps n the full 500 at one time. Also remember the 500 cfm 2bbl will not flow as much air as a 500 cfm 4bbl because the 2bbl is rated at twice the vaccume leval the 4bbl is. The 500cfm 2bbl is about the same size as 1/2 of a 750 4bbl.

The 2bbl will be a little too much at low speeds and low throttle angles but not flow enough at WOT at higher RPM. Either c be made to work decent but I would still take the small 4bbl.

A 600 4 barrel would be my first choice but the 500 2 barrel will work fine, throttle response should be fine on a 273.

I used to run a 500 holley on a 120cid 4 cyl and never had a throttle response problem, it would light them up whenever I wanted, do donuts and get rubber in 4 gears