First off we will look into hoe to calulate engine displacement, which is actually a bit of simple math.  First one needs to know the bore of a certain cylinder – say 4.00″ – and the stroke of the crankshaft on that cylinder – say 4.00″ .  If we take the bore of the cylinder and multiply it into the formula for the area of a circle, which is πr^2, (π being equal to 3.1416 for all intensive purposes) then we get 3.1416 x 2.0^2 which is to say 3.1416 x 4, which is equal to 12.5664 this then is simply the area of the circular portion of the cylinder, which then must be multiplied by the stroke of the cylinder to get the diisplaced volume of th ecylinder. When we do this we get 12.5664 x 4.00 which is eaual to 50.2656.  If we multiply that by eight, which is getting slightly ahead of ourselves and our involvement here, we get 402.1248 – for all intensive purposes a 400 cubic inch engine.

Now that is just the swept volume of the cylinder, which really doesn’t tell you a whole lot unless you are looking to calculate compression ratios.  To do this accurately you need to first convert the swept volume to cubic centimeters (cc’s) seeing as that is how most combustion chambers are measured.  The conversion factor for inches to cemtimeters is one inch to 2.54 centimeters.  So to be absolutely accurate we will convert the bore to centimeters – 10.16 – the stroke then is also 10.16 cm; so now we divide 10.16 by 2 to get 5.08, or ‘r’.  We insert that into our equation, getting 3.1416 x 5.08^2 or 81.0732.  If we multiply that by the stroke, we get 823.7036.  Now, if we decide to install a 70 cc combustion chamber over this cylinder, we take the swept volume – 823.7036 and add the 70 cc’s to it to get the overall cylinder volume (as a side note, the head gasket needs to be taken into account as well, and those vary quite a bit, so we will take one of .050″ and calculate that) which results in 893.7036.  Now we must calculate the aforementioned gasket area, so we’ll take a gasket that is .030″ over bore – normally they are more, but this is an example after all – so we get our bore of 4.030″ or 10.2362 cm and an area of 82.2938 cm, multiplied by our .050″ (or .127 cm) to get 10.4513 cc’s.  Add that to our 893.7036 and we get 904.1549.  What is all this, this is the total volume of the cylinder including the head gasket and combustion chamber. It does not include the slight amount of “squish” around the cylinder before you get to the first compression ring. Be that as it may, if we take this volume and divide it by the size of our combustion chamber, we get 904.1549/70.00 which comes out to 12.91:1.  Bear in mind that this is a fairly thin head gasket and the combustion chamber size is fairly small as far as that goes.  This is a stout compression to say the least, and it would require the running of some seriously high octane gas.

Now that we know that little bit of engine math, we shall look into the efficiency of combustion between cylinders in the next installment.