All Six CFM - does 2V or 1V matter?

[customline]

I have a question - if an engine of a given size has a requirement of, say 250cfm …… does it matter if it gets it from a carburetor rated to flow at 250cfm whether it is 1, 2, or 4 barrels? I have seen things implying that a two barrel specifically is preferred over a one barrel due to the larger Venturi area…. So my question is if it is really a matter of air requirement, wouldn’t it be the same so long as it is getting the required cfm of air/ fuel?

 

[78_200_C4]

1 + 2 barrel cfm ratings are not tested at the same vacuum as a 4 barrel.
A 250 cfm 1 barrel only flows 176 cfm when rated as a 4 barrel.
I have read and from my experience a 2V gives better low end torque.
I don't know of a 1 barrel that can flow what my stock enginetech 256 cam 200 wants at higher rpm which is up to 5,300 rpm.
"One and two barrel carbs are rated at 3 inches of pressure drop through the carb, while all four barrel carbs are rated at 1.5 inches of pressure drop, which is more accurate. For example; a Holley 500-2V carb flows 380cfm when it's rated like a 4V carb."

 

[78_200_C4]

The log head six likes 2 air fuel mixture plumes one for each of the 3 cylinders.
This provides more low end torque and throttle response off idle and at low throttle angles.
The 2V also can provide a very much larger CFM flow at WOT and higher rpm which can blow out the guts of old 2" turbo mufflers.
My D7 head enlarged intake bore 200 runs great with a large base Rochester Marine 500 cfm (V8 rated) 353 CFM (1-2 V rated) China clone carb.

 

[Cox Custom Mechanical]

78_200_C4 is on the money.

You can actually make good torque from a single carb with a little port divider and some creative porting to help get the air moving to the furthest cylinders.

One day I will put together a dyno mule to show the differences between a nice 1V head and a modified log with a 2 barrel Weber and intake port divider. I think the numbers will surprise a few people.