 Valve timing isn't just about making optimal power performance and fuel economy, appropriate timing also makes sure that your engine doesn't destroy itself by smashing all its guts together. Try to remember some of the basics of CQC. What does the term interference mean when referring to an engine? The short definition is that an interference engine is one where the pistons and valves are capable of making contact with each other if the piston is at top dead center and the valves are open at the same time. A non-interference or free running engine means that the pistons and valves cannot make contact regardless of position or timing. But why does that matter? The most common and frequent case is related to the engine's timing belt or chain. If you've got an interference engine and your timing belt fails, that's the thing that keeps the pistons and the valves from having a metallic make-out session. Also, valve and piston clearance isn't the only concern. Some engines can experience a valve interference. It's basically the same problem, but instead of valves and pistons touching, the opposing exhaust and intake valves can hit each other if timing is off by now. That's why it is super important to service your belt or chain properly. ProTube! In most cases, a timing belt doesn't just randomly fail. Usually, another part related to the belt is the actual cause of the problem. So just slapping on a new belt at the right time isn't a guarantee you're safe until the next service interval. While you're in there, take a closer look at all the moving parts that interact with your timing system. You might find something that needs to be replaced and it'll save you a big headache later. And improper maintenance isn't the only way these parts can end up colliding. The OEM designed some safety measures into the ECU and the engine that can be bypassed in the process of modifying a car. So if you're not careful, there's some risk in doing so, whether that's through a big mistake in ECU tuning or an engine building. So, moral of the story, when it comes to timing related performance mods like cams, valves, custom tuning, etc. Or if you're just doing common maintenance, make sure you know what you're doing or pay somebody that actually does. Because interference might just ruin your date and make you miss the Super Bowl. Oh, I mean blow up your engine.