As I understand it, Yoshimura built this bike for retired motocross and supercross star Larry Ward to ride for an industry ride in Colorado. In general, Colorado rides feature less air molecules than most rides, since trail days often start at more than a mile high and go up, so a certain amount of properly jetted horsepower is desirable. Crossing a Rocky Mountain pass, I've had an improperly jetted open four-stroke feel like an asthmatic XR100, so I can imagine a call from Larry Ward to Yoshimura: "Guys, make sure the thing can handle the altitude." When you talk with engineheads like the Yoshimura crew, innocent statements like that take on a life of their own.I know that Larry is an animal on a bike and I saw him podium a GNCC when he was semi-retired, but I doubt even he was in the market for this much power for a rocky, slippery Colorado ride. No doubt he had heard stories about the docile nature of a stock X and asked for more, but Yosh technicians stripped the engine, polished the transmission parts, ported the head, slapped in billet cams and hogged the cylinder out until the CP high-comp piston made it a 500X.Getting a little crazy for a trailbike didn't stop with the engine. The bike was stripped to the frame and the bones were powdercoated black. Factory Connection added suspension that a star factory pilot would expect, and the legs were backed by a chassis with abundant off-road goodies, sick brakes and eye-popping wheels. It was almost too pretty to ride, but we managed.As we wondered how Big Bird liked this cruise missile in the rocks, we were pleased Dirt Rider has nearby desert with plenty of room to exercise a herd of horses like this 450-ish X has. If you didn't have a stock X along, perhaps the 500 wouldn't have seemed so impressive. The prodigious boost is generated in a smooth fashion much like a stocker but wildly amplified. One ride on a stocker focused the reality: This thing is a monster, but a friendly one. It remains docile enough (if you are careful with throttle inputs) to handle tight trail riding, but dial up the excitement with the right grip and things get interesting.It is proper that the bike is a 500, because in some ways it acts like the old 500cc two-stroke MXers did. When you are hammering the bike for acceleration, it will spin easily in slippery conditions, but suddenly and without much warning the rear will grab and the front wheel will burst off the ground in a sudden wheelie. Good thing the Hinson-tuned Honda clutch is better than a CR500's.So it should be obvious that this bike has a fun factor off the charts when there is room and traction to play with the power. The suspension, tires, brakes and controls all help make the package a pleasure. The exception was in loose, sandy conditions. The stock X has a pretty good "lunge" in the delivery at about a quarter throttle. Amplify that lunge via a full-race 500, and the bike can dig itself into a hole in a heartbeat on soft, technical climbs. If you are looking for the old-time thrill of a two-stroke 500 without the misery of vibes, violent delivery and kickstarting, Yosh has the answer.