https://www.mathsisfun.com/geometry/circle-area.htmlThe inside diameter of the main jets can be found on line or in several different books. The diameter of the PVCRs can be found by measuring with drill bits.
The decimal points can make calculations more difficult. So just eliminate them. As long as you remain consistent with the position of the decimal points throughout the calculations, they don't affect the outcome for this.
Let's say you have #75 main jets and .068 PVCRs.
#75 main jets have a listed diameter of.082. Eliminate the decimal point and take half of .082........041 and then multiply it by 3.14 and then by that number again.
So, 41 x 3.14 = 128.74 Then multiply 128.74 by itself (squared) = 16,574
Do the same for the PVCRs, half of .068 is .034.
So 34 x 3.14 = 106.76 x 106.76 = 11,398.
Whatever area (flow) you take away from the mains (16,573), add that much to the PVCRs (11,398) so that the total of the 2 stays about the same. Most Holleys seem to be fat on the cruise, but are usually close on the WOT. So you usually need to step down on the mains and then go larger on the PVCRs.
You do not need to include both both mains jets and both PVCRs in your calculations. Although you make the same changes to each pair, you only need to calculate the volume of one of each.
Don't worry that this procedure isn't perfect. It will get you close enough on the balance so that the final tune will be easier to achieve.
Oh, and one last thing. Make sure that your car is actually cruising on the mains. I have encountered more than one big engine with a big carb and low gears that actually cruise on the idle circuit due to the small throttle blade opening. As a good rule of thumb, the farther over 2,000RPM that you're cruising, the more likely you are to be on the mains.
IHTH Trying to keep this simple.
