Happy Easter all. In my quest to not only learn more about Mopar engines, my own engine and car, and automotive mechanics in general, I've been asking a series of questions over the last few weeks. Honestly, it's mostly to keep my sanity as my work has dried up because if Covid-19. So here is the next question: How accurate is the CFM formula? Here why I ask. After speaking to a handful of professional engine builders, they pretty much agreed on one thing that first time engine builders make mistakes on. They over cam, and go too big on carburetion. Now for my build, my original idea was to go with an original 1970 440HP cast iron intake and 1970 Carter AVS carb which flows 625 CFM. Then I decided to go Eddy RPM intake and a new carb, like a Holley or Eddy in 750-800. Money has dried up because of no work, but I still have to finish paying the engine builder. another $1200 for the new intake and carb will be very difficult to justify right now. Gotta keep the fridge full obviously. So I'm 90% sure I'll stick with what I have for now, as I already own it, and can upgrade later. Now, back to CFM. The formula is:
The formula for calculating how much CFM (cubic feet per minute) your engine requires is: CFM = Cubic Inches x RPM x Volumetric Efficiency(?%) รท 3456.
The volumetric efficiency is a bit of a mystery. If you watch Pete's Garage on YouTube, he explains it far better than I can. I'll link it below.
https://youtu.be/xAW3g-qz0_USo if my engine is say, 90-95%, then that puts my CFM at 605-635. Now that's at 5200 rpm, which is the number I used as I will rarely be above that. So maybe some input from you guys as to how you figure how big a carb to run for your requirements. Have a great and safe day all.
