Cubic Inches to CCs

Mike Roen is sharing a couple simple math equations that will help to answer some very common questions pertaining to engine displacement. Oftentimes you will know an engines size in cubic inches but want to know what the engine size is in cubic centimeters. To make the conversion, there is a basic math formula that is very easy to remember. Here is an example with some common Twin Cam engine sizes:

– 88 cubic inch motor: 88 ÷ .061 = 1442.62 CC. Harley Davidson rounds this cubic centimeter result up to 1450.

– 95 cubic inch motor: 95 ÷ .061 = 1557.37 CC. Harley Davidson rounds the cubic centimeter number down to 1550

– 103 Cubic inch motor: 103 ÷ .061 = 1688.52 CC. Harley Davidson rounds this up to 1690 CC.

On the other hand, you may know a motors displacement in Cubic centimeters but want to know the size in cubic inches. When this is the case, simply take the same number (.061) and multiply it by the known cubic centimeter number. For instance: 1690 cubic centimeters x .061 = 103.09 cubic inches.

Another important number to have in your memory bank is 25.4. You can multiply or divide by this number in order to convert American to metric or metric to American. Mike gives us a couple of examples:

You have a 2 inch part and want to know it’s metric equivalence. 2 in. × 25.4 = 50.8 millimeters
If you have a metric measurement and want to know the American equivalence, you will divide by 25.4. 2mm ÷ 25.4 = .07874 in.

When it comes to drill bits, there are number and letter size drill designations but, most commonly drill bits have designated sizes by fraction. Sometimes, you may need to know the drill bits fractional size in American decimals. Here is an example of how to achieve this:

If you have a 7/8″ drill bit; divide the bottom number into the top number. 7 ÷ 8 = .875. Keep these simple formulas near your work bench. They will come in handy.