like traditional combustion engines come in many shapes and sizes, but they all follow four basic steps: intake, compression, combustion, and exhaust. Whence these steps, car movement.

If you’re going to mass produce cars, chances are you’ll want to pick a style of engine that does these four steps efficiently and without undue weight or cost burdens.

But for Hemi enthusiasts, these bugs are actually features. Here’s a bit about the Hemi engine, and which car company made it their whole personality.

Areas and volumes and ratios, oh my

Those four steps have introduced interesting opportunities and challenges for automakers over the years. What is the ideal way to arrange the pistons, cylinders, and other engine components to maximize power and minimize inefficiency?

The name of the game, says

Engineering Explained

, is ratios. When a piston travels up and down inside a cylinder, compressing and then releasing the fuel and air that is introduced via the intake valves, it’s generating a level of power that varies based on its own shape, and the shape of the chamber.

And the ideal ratio is one of higher volume to surface area. What does this mean? Basically, a flat-topped cylinder interacting with a flat ceiling has a large surface area, and more surface area means more heat absorption. And more heat absorption means less power generated.

So if a cylinder/piston combination can optimize for volume, rather than surface area, then the heat that would have been lost will instead be transmuted into power.

Spheres and hemispheres, it turns out, do a great job maximizing the volume-to-surface area ratio. A rounded chamber and a rounded piston solve the heat absorption problem. No pesky corners means no “heat spots and unusual stresses,” as Engineering Explained calls them.

This “hemispherically shaped combustion chamber” is also known as a Hemi.

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Chrysler goes Hemi

But this ratio isn’t exactly golden. A hemispherical shape has its inefficiencies in other places—it’s heavier, and it’s hard to incorporate multiple hemispherical shapes within one engine without it quickly devolving into a complicated tangle. For many automakers, the troublesome weight and space problems weren’t worth the trouble.

Chrysler was not one of these. Seeing instead the massive power that could be generated from a Hemi engine, the company took a chance on these heavy, difficult engines. In the 1950s, Chrysler began producing its FirePower engines, says

Auto.com

, and these formed the basis of its formidable contributions to the muscle car market.

Though these angled Hemi engines required some fancy finagling to fit inside an engine (the “double rocker arm” structure made it possible), the added expense and difficulty proved to be well worth it. Hemi engines catapulted Chrysler into history—ever heard of the Dodge Hellcat? A trademarked HEMI engine powers this 707-hp legend. Chrysler can look back fondly on these heady Hemi times.

MORE: The Chip Shortage May Finally be Ending

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