For the sake of simplicity, let's work with a cylinder that displaces 9 cubic inches, and a combustion chamber that displaces 1 cubic inch. When the piston is at BDC, the total of the cylinder and the chamber is 10 ci. When the piston is at TDC, the total volume remaining is 1 ci. 10 divided by 1 = 10, hence a 10:1 comp ratio.
Now, let's reduce the volume of the combustion chamber by 50% with a real aggressive milling job on the head. Now, at bdc, we still have 9 ci in the cylinder, but only .5 ci in the chamber. With the piston at BDC, our total is 9.5 ci. With the piston at TDC, our total is .5 ci. 9.5 divided by .5 = 19, and a 19:1 comp ratio.
If we go the other way, and put on a new set of heads with 2 ci chambers, we have a total at BDC of 11 ci, and 2ci at TDC. 11 divided by 2 = a CR of 5.5:1.
To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.