Now that i'm thinking about this....does anyone know what the cfm rating would be on a 65-70mm throttle body? I'm curious what size carb flow that would equate to. Another thing i was thinking about was how a lot of Ford's show cars have duel CAI and duel throttle body setups...i wonder why?
A large throttle body does not hurt low-end power.
It is just a valve that lets air in the engine. This is the same reason why a 4.00" pipe will not hurt.
Either way you attack it, just keep the intake tubing size area consistent (tube, MAF, TB).
Throttle Body CFM Flow Ratings for the 5.0L:
Stock 5.0L 60 MM - 526 CFM
SVO 65 MM - 540 CFM
Accufab:
65 MM - 664 CFM
70 MM - 787 CFM
70 MM - 896 CFM (Race version)
75 MM - 924 CFM
75 MM - 1045 CFM (Race version)
80 MM - 1142 CFM
85 MM - 1322 CFM
90 MM - 1369 CFM
105 MM - 1550 CFM
Holley:
65 MM - 750 CFM*
70 MM - 790 CFM*
75 MM - 840 CFM*
80 MM - 892 CFM*
*Information given by Tech Rep.
BBK:
70 MM - 726 CFM
Dual throttle body set-ups are for packaging reasons and it is also a bit easier to control (think throttle modulation) two small blades, than one big blade.
Throttle Body Blade Area:
One can figure out the area by a simple formula. Take the millimeter measurement and divide by 25.4 to get the inches across at the blade. Take that number and use it to find the area of the blade. We will use the area of a circle, which is roughly the shape of the throttle body blade and will give a good estimate.
The area of a circle is PI x radius x radius. The radius is half of the diameter of the blade or circle.
Example: 60 mm/25.4 = 2.36. 2.36/2 = 1.18. Then 3.14 x 1.18 x 1.18 = 4.38” (squared).
58 mm - 4.09”
60 mm - 4.38”
65 mm - 5.14”
70 mm - 5.96”
75 mm - 6.84”
80 mm - 7.79”
85 mm - 8.79”
90 mm - 9.86”
95 mm - 10.98”
105 mm - 13.41”
The twin throttle bodies are a little different. You need to add the areas together of each individual blade, so the areas are:
57 mm - 7.90”
62 mm - 9.36”
65 mm – 10.28”
NASCAR is in the 125% VE with 358 cubic inches. They also run 750-830 CFM carburetors. Could they make more power with a larger carburetor? Very possible, but it shows you that the restriction is small, considering they are making near the 850 HP mark.