How many CFM carburetors do I need?
When it comes to choosing the right carburetor for your vehicle, one of the key factors to consider is the cubic feet per minute (CFM) rating. The CFM rating indicates the maximum airflow capacity of the carburetor, and it's crucial to select a carburetor that can provide the appropriate amount of airflow for your engine's needs. In this article, we'll explore how to determine the number of CFM carburetors you need for your specific application.
Understanding CFM Ratings
The CFM rating of a carburetor is a measure of the maximum airflow capacity of the unit. This rating is typically expressed in cubic feet per minute (CFM) and can range from as low as 150 CFM for a small four-cylinder engine to as high as 1,000 CFM or more for a high-performance V8 engine. The higher the CFM rating, the more air the carburetor can flow, which is essential for producing more power.
Factors to Consider
When determining the number of CFM carburetors you need, there are several factors to consider:
- Engine Displacement: The size of your engine, measured in cubic inches (CI) or liters (L), is a primary factor in determining the required CFM. As a general rule, you'll need approximately 1 CFM of carburetor airflow for every 1 CI of engine displacement.
- Engine Modifications: If your engine has been modified with performance parts, such as a larger camshaft, ported and polished heads, or forced induction (turbocharger or supercharger), you may need a higher CFM carburetor to match the increased airflow requirements.
- Intended Use: The way you plan to use your vehicle, whether for street driving, drag racing, or high-performance applications, will also influence the CFM requirements. Vehicles used for high-performance or racing applications generally require higher CFM carburetors to support the increased power demands.
By considering these factors, you can determine the appropriate number of CFM carburetors needed for your specific engine and application.
Calculating the Required CFM
To calculate the required CFM for your engine, you can use the following formula:
- Engine Displacement (CI) ÷ 3.5 = Minimum CFM Requirement
For example, if you have a 350 CI V8 engine, the minimum CFM requirement would be:
- 350 CI ÷ 3.5 = 100 CFM
This means you would need a carburetor with a minimum CFM rating of 100 to support your engine. However, it's generally recommended to choose a carburetor with a slightly higher CFM rating to provide a safety margin and accommodate any future engine modifications.
Remember, these are general guidelines, and the actual CFM requirements may vary depending on the specific details of your engine and intended use. It's always best to consult with a qualified mechanic or performance specialist to ensure you select the right carburetor for your needs.
Is a higher CFM better for a carburetor?
Carbs with a higher cfm rating will have larger barrels. But, bigger is not always better. At wide open throttle, the carburetor barrels are big holes in the intake.
How much horsepower will a 750 cfm carb support?
As an example, a 750-cfm carb on one of my street/strip Chevy 383 small-blocks can make more than 600 streetable hp, whereas an engine less well spec'd may only make 540 to 550. For what it is worth, it is possible to get the BSAC figure below 5 lbs/hp/hr.
How do I choose CFM for my carburetor?
To arrive at the most appropriate carburetor choice, there's a basic formula: engine displacement multiplied by maximum rpm divided by 3,456. For example: a typical 355ci small-block—a 0.030-over rebuild—with a 6,000-rpm max engine speed would work well with a 616-cfm carb ((355 x 6,000) 3,456 = 616.32).
What CFM carburetor for 350?
A 600-cfm carburetor may perform quite well on a stock 350 Chevy. However, the minute you start weaving in power adders like a hotter cam, a dual-plane performance intake manifold, and aluminum heads you're going to need 700-750 cfm.
Is a 600 cfm carb big enough for a 350?
600 and 650 is enough for a Chevy 350. the right carb for your buick 350 is a 750 cfm quadrajet.
What CFM is a stock quadrajet carb?
Most Quadrajets were capable of 750 cu ft (21,000 L)/min (cfm) maximum, but some rare Buick and Pontiac models were capable of 800 cu ft (23,000 L)/min for use on high performance engines, and most 1984-1987 pickup trucks were also equipped with the 800-cfm carb.
What size carb for 400 hp?
Typically for the size selection you need to know approx. horsepower (be honest). 600 cfm carbs best suited for low 300hp, 650cfm 340hp-390hp, 750cfm 400hp-460hp, 950cfm 490hp-575hp 1000cfm 575-595, 1050cfm-1250 600hp and up.
How do I figure out what CFM carb I need?
To arrive at the most appropriate carburetor choice, there's a basic formula: engine displacement multiplied by maximum rpm divided by 3,456. For example: a typical 355ci small-block—a 0.030-over rebuild—with a 6,000-rpm max engine speed would work well with a 616-cfm carb ((355 x 6,000) 3,456 = 616.32).
Will a 650 CFM carb work on a 350?
However, on the AFBs there is a velocity valve which limits the secondary air flow so that you can use a slightly larger carb. It allows the 625 carb to work on a range of engine sizes. That's why Edelbrock sells the 625/650 cfm carb for 350s in general.
How many CFM do I really need?
To determine your ideal CFM, multiply your kitchen's cubic feet by 15. For instance, 1,500 cubic feet x 15 air exchanges = 22,500 cubic feet per hour. Now, divide your total by the number of minutes in an hour: 22,500 cubic feet / 60 minutes = 375.
