What does cfm mean on a carburetor

The question is, do we know the required cfm for our carburetor, and, if not, how to calculate the cfm of your engine? This engine cfm calculator gives you an idea of the carburetor size you need for your engine! That's all down to the Bernoulli equation , which is the same principle that carburetors work on.

Carburetors can be thought of as a pipe that pumps more air into the engine as you push on the accelerator. This pipe passes through a venturi , which is connected to the fuel intake.

A venturi is a slightly narrower area of pipe which causes air to speed up when passing through it. To conserve mechanical energy, an increase in the air's speed must be met with a decrease in pressure, and this decrease in pressure is enough to draw fuel from the fuel intake into the airflow.

The quicker the air's initial movement, the more it's speed increases by, which causes a lower pressure, drawing more fuel into the airflow and engine. When the fuel gets sucked into the engine, we've achieved what we wanted, but how the air-fuel mixture can be adjusted?

There are two valves above and below the venturi. The valve at the top is called the choke and regulates how much air can flow in. If the choke is closed, less air flows in which reduces combustion in the engine due to lack of oxygen. On the other hand, the valve at the bottom is called the throttle. When the throttle valve is open, the air inside the carburetor increases, increasing both the air and fuel amount in the engine.

Nov 30, 5. Messages: 2, Likes Received: Depending slightly on your performance goals street, track, race , the best fuel economy and performance is had with ci engines running cfm carbs, and engines greater than ci running carbs larger than cfm, usually 's.

On the other hand, some owners will venture out on to the public street with two cfm carbs ,or larger, "blown" by forced air intake! Not good gas mileage. Tough on treadwear. Nov 30, 6. And the Qjet is a good choice because the engine runs on a slightly smaller pair of intake bores compared to the squarebore carbs until you put your foot down, and open up the secondary bores a BIT larger than the squarebore carb secondaries!

Hence, better average gas mileage if you keep your foot out of it, and then it goes downhill fast if you don't!! You must log in or sign up to reply here. Show Ignored Content. Share This Page Tweet. Your name or email address: Do you already have an account? No, create an account now. Will a bigger carb make more power? Recently the Engine Masters show on the Motor Trend On Demand site did a comprehensive test to see just what differing sized carbs would produce.

Here is what they learned. A better than average HP street performance engine. Now this series of dyno pulls was on the Westech Performance dyno. Probably one of the best facilities around. Here is what they found. Remember these numbers were from wide open throttle. So, will a bigger carb make more power? Looks like bigger is not always better. If this was to be a or engine street driven just for pleasure, the will give the best all-around performance, excellent throttle response, good fuel mileage, great low and mid range performance.