Engine Displacement

This one is for all of you younger Hot Rodders out there who have been looking for a simple article explaining Displacement, Bore and Stroke but only found Wikipedia and a bunch of forum threads. Some of these forum threads may actually be helpful but you’re not sure if you should trust these forums, so you want a real article and not a wiki. So I decided to write this and help people like you out.

            First thing is first lets, go over what engine displacement is, if you are into hot rodding you already know the names of several engines such as the Chevy 350, Ford 302, Chrysler 440, etc. Well the numbers are the cubic inches of engine displacement. What engine displacement is, it is the measure of how much fuel and air you can fit in your cylinders.

            Now how you figure out engine displacement is by a simple calculation (oh no, not math!) Now how you figure out displacement is

∏(3.14)/4  X  bore (squared) X stroke X number of cylinders

An example the Chrysler 3.18 LA

3.14/4 X 3.91^2 X 3.31X 8= 317.79ci (aka 318ci)

Now some of you maybe be wondering why use PI? Well because Cylinders are round and we are figuring out a volume, PI is used in volume so it is used to figure out engine displacement which is volume. As for those wondering why the 318 LA in the example, well because the SBC 350 is to common.

Now for those of you who are too lazy to use paper, there are plenty of online displacement calculators for your convince. The best one I have found is here at the csgnetwork, not only does it calculate displacement it shows you all of the bore, and stroke for all of the stock hot rod engines. That way when you bore it out, or do a custom stroker job, you can calculate it right there.

Now getting on to bore (yes you’re calculator will come in handy for this), watching or attending drag races you may have heard people say they something like this “I’ve got a 350 SBC, 30 over…” which is the most common. What the 30 over means (its actually written out .030) is that he bored out his cylinders by thirty thousands of an inch increasing his displacement which if he didn’t stroke the engine it would bring it too 355.

Now you have probably heard of stroker motors, such as the 383, the 331, the 496, etc. What is a Stroker motor you may ask? Well first lets go over stroke.

What Stroke is the measurement of how far down a piston is from the Top Dead Center of the Cylinder to the bottom dead center of the Cylinder. As mentioned early the 3.18 has 3.31ci of stroke, that is 3.31 cubic inches from the Top Dead Center of the Cylinder to the Bottom dead Center of the Cylinder.

A Stroker motor is when you increase the engines stroke so the piston distance can increase and more fuel and air can get in the cylinder. To do this you will need to bigger crankshaft and longer connecting rods for your pistons.

Now I hope that helps you guys out. If you are planning one doing a bore or a stroke job please research it before you do it! Most engines have kits available for both so look into that as well. If there is any engine that you want me to do a tech article on I will do that.