Compression test kits do just what they say: measure the ability of each cylinder of your engine to combust the fuel/air mixture without losing any of the resulting energy.

Unique compression technology and an improved ratio of fuel economy to performance made the Skyactiv-X engine promising, but the U.S. never received it.

It works like this: The engine makes hydrogen from gasoline using its own heat and a catalyst. It then burns that hydrogen ...

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?