How to Determine the Best Carburetor CFM Size to match your build!

Hey, Dave from First Place Auto Parts here! Following up on our previous video about square bore vs. spread bore carburetors, we received tons of questions about how to determine the right carburetor size for different applications. Today, we're delving into the world of CFM ratings (Cubic Feet per Minute) to help you understand the magic behind choosing the perfect carburetor for your ride. Stay tuned for some valuable insights, and remember, sometimes bigger isn't always better!

🚨 **Video Highlights:**
- Recap of the square bore vs. spread bore carburetor video and viewer requests for carburetor sizing insights.
- Exploring the importance of selecting the right carburetor size for optimal performance and drivability.
- Showcasing a 600 CFM and 750 CFM vacuum secondary Holley carburetor for visual comparison.

🔍 **Understanding CFM Ratings:**
- Defining CFM (Cubic Feet per Minute) and its significance in carburetor sizing.
- Discussing the misconception that bigger is always better and its impact on performance and cost.
- Teasing the idea that sometimes "bigger isn't always better" and hinting at the consequences of having too large a carburetor.

📊 **Carburetor Sizing Formula:**
- Introducing the three crucial numbers for sizing: cubic inch displacement, max RPM, and volumetric efficiency.
- Sharing the formula: (Cubic Inches × Max RPM × Volumetric Efficiency) / 3456 = Theoretical CFM Demand.
- Emphasizing the importance of accurate data for cubic inches, max RPM, and volumetric efficiency.
- Touching on the different volumetric efficiencies for street cars (80-85%) vs. race cars (90-110%).

🔢 **Application Scenarios:**
- Running through a hypothetical scenario for a 350 Chevy with a 6000 RPM limit and 85% volumetric efficiency.
- Illustrating how the formula calculates the theoretical CFM demand (516 CFM) and relating it to carburetor selection.
- Discussing the impact of engine characteristics on carburetor size, using examples of 600 CFM and 750 CFM carburetors.

🛠️ **Tuning Considerations:**
- Addressing the tuning challenges associated with oversized carburetors, including secondary springs and jetting.
- Sharing personal experiences with a gasser-themed car and twin 600 CFM carburetors on a 454 cubic inch motor.
- Encouraging honesty about the car's application to avoid tuning hassles and achieve optimal performance.

💡 **Choosing the Right Carburetor:**
- Advocating for smaller carburetors to enhance throttle response, reduce tuning hassles, and improve overall drivability.
- Emphasizing the importance of buying the right size carburetor from First Place Auto Parts, offering a range of Holley carburetors and tuning components.
- Addressing common issues of rich-smelling cars at car shows due to carburetors that are too large for the application.

🔗 **Conclusion and Call-to-Action:**
- Wrapping up with a call to subscribe to the First Place Auto Parts YouTube channel for more insightful videos on parts, installation guides, and car enthusiast content.
- Expressing gratitude for watching and inviting viewers to understand the science behind carburetor sizing for a smoother and more enjoyable ride.

🚗🔧 #CarburetorSizing #CFMRatings #CarEnthusiast #FirstPlaceAutoParts

[dewholdingsllc]

Thanks for the content. I’m trying to find better easier carb to rebuild and tune than the OEM autolite 4300 that came on my 72 429 Ford; probably a complimentary intake manifold also. Keeping it stock would be nice but so far the old 4300 isn’t really a good carb worth messing with. My 2cents.

[dynodon]

Electric motor, gas engine .Just buy the H.P. book on Holley carbs. Money well spent. I bought mine in 1971.

[michaelgarrow]

I have a Holly 1100 on my lawn mower…
It’s good to 125, 000 rpm

[doomman]

Regardless of rating, you will only use the cfm the engine pulls.

[cuzz]

"Having too high of a CFM rating for the project the vehicle will run lean. Too low and the car will be running to rich."
I dont think this is accurate. You adjust the amount of fuel to match the air so you arent lean or rich. too big you end up with a poor signal and as you stated hurts your throttle response.

[gila-clifffirewood]

That's an old, outdated, disproven equation for calculating CFM needed.