If the volume of a cylinder with the piston at bottom center is 84 cubic inches and the piston displacement is 70 cubic inches, what is the compression ratio?

To determine the compression ratio of the cylinder, you need to understand how it is calculated. The compression ratio is defined as the ratio of the total cylinder volume when the piston is at the bottom of its stroke (BDC - Bottom Dead Center) to the volume at the top of its stroke (TDC - Top Dead Center).

In this scenario, the total volume of the cylinder when the piston is at the bottom center is given as 84 cubic inches. The displacement volume, which is the volume that the piston moves through between BDC and TDC, is provided as 70 cubic inches.

The volume at TDC can be calculated by subtracting the displacement from the total volume. Therefore:

Volume at TDC = Total Volume - Displacement

Volume at TDC = 84 cubic inches - 70 cubic inches = 14 cubic inches

Now, the compression ratio is calculated as:

Compression Ratio = Total Volume / Volume at TDC

Compression Ratio = 84 cubic inches / 14 cubic inches = 6:1

This calculation shows that the correct answer is indeed 6:1. Understanding this concept is key to recognizing how engine design factors into cylinder efficiency and performance, as compression ratios directly influence power output and fuel combustion.