Check out this engine compression test, leakdown, and bubble tests. Read more only at www.highperformancepontiac.com, the official website for High Performance Pontiac Magazine!

Some engines use a spark to ignite their fuel, and others rely on compression. What does all of that mean? And how do the two kinds of engines differ?

HCCI engines have a compression ratio of 12:1 (similar to that of a conventional direct-injected gas engine), so they can run on regular pump gas and E85.

Knock has historically been one of the main limitations on spark ignition (SI) engine compression ratio and hence efficiency. The trend to downsizing or rightsizing in recent years, driven by ...