A man pouring block filler into engine block in a garagePouring concrete into your engine block might sound like something out of a gearhead's nightmare. If merely putting the wrong oil in your engine can lead to catastrophic damage, just imagine what filling it up with the hard stuff can do. But, it turns out that — if done right — adding concrete into an engine can actually make it stronger and able to hold up to the extreme performance conditions of all-out drag racing instead. Just note that, while some folks have resorted to actual concrete for the job, companies today produce dedicated engine-block fillers for the same purpose. In either case, however, the key is exactly where the concrete (or block-filler) goes.To understand how this works, keep in mind that the typical engine block is not truly a solid block of metal. Beyond the actual cylinders bored into it, the block further features small channels for coolant. They allow the coolant to reach throughout the engine, but those same spaces can act as structural weak points. Consider an engine under a heavy load: the natural vibrations of the engine can cause the metal that's around the channels to flex out of shape and even crack the engine block. Filling those spaces with a solid material helps prevent the flexing and keeps the engine in its proper shape. With an unfilled engine, those vibrations can be extreme enough that the cylinder walls lose their original shape, resulting in a mismatch between the cylinder shape and the pistons, for example. Filling blocks is better for short bursts of powerA man adding block-filler to his engineRemember, there has to be a proper seal between each piston and the cylinder walls for optimum compression and combustion to take place. If the cylinder walls have bent even slightly, the rings can start leaking, and that's where the problems begin. It's essentially the same as what driving with bad piston rings can do to your engine. As one scenario, if exhaust gases get by the rings –- a situation known as "blow-by" — they can chemically react with engine oil to prevent it from doing its job. Filling the block with concrete or block filler can also limit the vibrations themselves. With the coolant channels packed with cement, there is less room for the metal of the block to move.Of course, then we get to the elephant in the room. Engine blocks filled with concrete no longer have operational cooling channels, which means they can be prone to overheating — at least over time. The reason block-filling is most common for drag racing is that dragsters generally need maximum engine power for only a few seconds. The thought process is that those seconds could last long enough for damage from engine vibrations to begin, but not long enough for temperatures to reach a dangerous point. A case in point is that when Shawn Langdon made the fastest drag-racing run ever, the history-making event was over in 3.724 seconds, during which Langdon reached 345 mph. Want more like this? Join the Jalopnik newsletter to get the latest auto news sent straight to your inbox, and add us as a preferred search source on Google.