Someone Built Every Major Engine Configuration Out of Lego — Using Only AirLego introduced its pneumatic system back in 1984, and it has remained a staple of the Technic line ever since, allowing builders to route compressed air through small tubes to drive pistons in reciprocating motion. Most people use it to make a toy excavator scoop up nothing in particular. One creator on YouTube decided to use it to build a working radial 12-cylinder engine instead.The build, documented across a lengthy video, starts at the absolute bottom: a manual pump, a valve, and a single cylinder. That three-part combination is the entire foundation of every pneumatic engine that follows – a pressure source, a directional control, and something to push. Moving beyond hand-powered operation, the builder advances to a homemade air reservoir constructed from six plastic bottles linked together, which a tire compressor charges via a conventional valve stem. The improvised reservoir gets the optimistic designation "Air Tank 12000." An earlier attempt using a small green bottle ended with the bottle popping off-screen and a "RIP" overlay on the dented remains.The Engineering Gets Serious FastWith a pressurized supply sorted, the testing begins in earnest. A digital tachometer tracks RPM across different cylinder sizes at 1 bar of pressure, and the results vary more than you'd expect: a standard cylinder turns in 53.2 RPM, the larger 2×11 version nearly doubles that at 99.6 RPM, and the slim 1×11 drops back to 27.3 RPM. The smallest cylinder, a 1×5, can't generate enough force to keep the engine moving at all.AdvertisementAdvertisementTwo modifications make an outsized difference. Boring out the airflow port on a cylinder and lubricating it with silicone oil – not WD-40, which damages the plastic – produces a meaningfully faster engine. The inclusion of guide sliders to keep the piston stable under load raises the engine's RPM from approximately 516 to 689. Crank radius follows the same tradeoff you'd find in a real engine: a 2-stud radius pulls more torque at 460 RPM, while a 1.5-stud radius trades that grunt for 540 RPM. A custom torque tester built from Lego clutch gears – which slip at defined Newton-centimeter thresholds – lets the creator quantify pulling power rather than just eyeball it.The engine lineup that follows covers essentially every configuration an internal combustion engineer would recognize. An inline-2 and a V2 produce similar speeds around 460 and 440 RPM respectively, with the V2 demonstrating how two cylinders can share one crankpin. The inline-3's crankshaft demands 120-degree spacing between throws, a requirement met in this build by a particular circular Lego component featuring three cross-axle holes.That three-cylinder pulls 5 Ncm through the torque tester. The inline-4, notably, runs on just two pneumatic switches and hauls 12.5 Ncm – a substantial jump. A V6 built on a custom 60-degree liftarm base ends up powering a small four-wheeled chassis across a table, after the creator fixes a hose routing mistake that had it coughing on startup. Eight 135-degree angle connectors give the V8 its evenly spaced power strokes across all eight cylinders, requiring just four switches to operate.The Radial 12 Is the Whole PointThe final build is a twelve-cylinder radial engine with all the pistons arranged in a circle around a central hub – the same layout used in WWII-era aircraft engines, scaled down to Lego.AdvertisementAdvertisementAt full pressure, the Radial 12 spins at 163.5 RPM. The more interesting test is the floor: the creator dials the airflow down to find the lowest speed the engine can sustain without stalling, eventually settling at 12.1 RPM – twelve cylinders turning in lazy slow motion, each piston visibly completing its full stroke.Two cats make uncredited appearances throughout. One white cat wanders in to sniff the pressure gauge and bat at the tubing. A second, fluffier ginger cat shows up to inspect the running inline-2. Neither seems especially impressed.The broader point the build makes is that Lego pneumatics, a system old enough to vote in most countries and designed to teach kids how excavators work, is a surprisingly complete toolkit for demonstrating real engine geometry. The 120-degree crank spacing on a three-cylinder, the even power stroke distribution on a V8, the torque-versus-RPM tradeoff on a crankshaft – all of it works out exactly the way it would in metal, just quieter and significantly less likely to catch fire.