This one’s for all the younger Hot Rodders who have been looking for a simple article explaining displacement, gauge, and stroke, but only found Wikipedia and a bunch of forum threads. Some of these forum threads may 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.

First things first, let’s review what is engine displacement; If you like hot rodding, you already know the names of various engines like Chevy 350, Ford 302, Chrysler 440, etc. Well the numbers are the cubic inches of engine displacement. What is displacement, is the measure of how much fuel and air can fit in your cylinders.

Now, how you find out the displacement of the engine is by a simple calculation (oh no, not math!) Now, how you find out the displacement is ∏ (3.14) / 4 X diameter (squared) X stroke X number of cylinders .

An example of the Chrysler 3.18 LA

3.14 / 4 X 3.91 ^ 2 X 3.31X 8 = 317.79ci (also known as 318ci)

Now some of you may be wondering why use PI. Well, because the cylinders are round and we are calculating a volume, PI is used in volume, so it is used to calculate engine displacement, which is volume. As for those wondering why the 318 LA in the example, well because the SBC 350 is very common.

Now for those of you who are too lazy to use paper, there are plenty of scrolling calculators online to convince you. The best I have found is here on csgnetwork, it not only calculates displacement but shows the entire bore and stroke of all stock hot rod engines. That way, when you get bored or do custom stroke work, you can calculate it right there.

Now to bore (yes, your calculator will come in handy for this), watching or attending endurance races, you may have heard people say something like “I have a 350 SBC, 30 over …” which is the most common. What the 30 over (it’s actually written. 030) means is that you bored your cylinders by thirty thousandths of an inch by increasing your displacement, which if you didn’t hit the engine, so would 355.

You’ve probably heard of Stroker engines, like the 383, 331, 496, etc. What is a stroker engine? Well, let’s review the coup first.

What Stroke is the measurement of how far down a piston is from cylinder top dead center to cylinder bottom dead center. As mentioned above, the 3.18 has 3.31ci of stroke, which is 3.31 cubic inches from cylinder top dead center to cylinder bottom dead center.

A stroker engine is when you increase the stroke of the engine so that the distance from the piston can be increased and more fuel and air can enter the cylinder. To do this, you will need a larger crankshaft and longer connecting rods for your pistons.

Now I hope that helps you. If you are planning one doing a punch or punch job, do your research before you do it! Most engines have kits available for both, so do your research as well. If there is any engine you want me to do a white paper on, I will.