2006 Thumper Racing Honda CRF500X Dirtbike - Dirt Rider Magazine

Lately our staff has been intrigued with Honda CRF450Xs that have smaller-than-stock engines, so what motivated us to try a bigger one? Partially, it was the other Thumper bike we've ridden recently: the KTM 570 XC. If there ever was a bike accused of too much power, the KTM 525 would be it, but a Thumper big-bore kit made it faster and more powerful yet, oddly, easier to ride. So maybe the kit would help the Honda CRF450X? As it turned out, it did. The bigger piston (in a Nikasil-plated bore) fills in most of the chinks in the 450X's armor. Unlike some big motors, the 500 doesn't feel any heavier or more difficult to ride, but there is certainly more power on tap. Certainly more than you would think from a piston a scant few millimeters bigger than a stock one. Have you seen 5mm? After all, the stock piston is 96mm wide. The Thumper-spec 101mm Wiseco slug doesn't look any larger unless you hold it up to a stock one.As soon as you roll on the throttle, though, you know the difference. The 500X has a more muscular, carry-the-front-wheel immediacy than even a stocker has. Those wheelies are coming far earlier in the rpm range. Even so, the engine is less prone to hiccup stalls than ever. Any issues the stock engine had with pulling gear spacing are totally gone. Thumper chose a more open FMF Ti Powercore, and though it barely made sound levels for California, the pipe passes. No doubt that exhaust was responsible for some of the amazing throttle response. In case you might be thinking the 500 is all torque-forget it. It still revs like all Honda 450s, and it makes big boost on top as well. But you actually end up screaming it less, since there is no need for that. Initially, first gear was a little tall, but a sprocket change to a 48-tooth rear was all it took to fix the problem.The Honda 450X already had a chunky, big-bore four-stroke feel to the power, and if you like that ground-pounding torque, then Thumper's 500 kit will make you grin every time you wack the throttle. And since it is a bore-only performance mod, longevity should be good. The cam and valve train remain stock. About the only negative is Honda's starter motor isn't overly enthusiastic about spinning the 500, and it grumbles a bit but never failed to fire.The ESP suspension wasn't quite the bull's-eye it was on the 570. The action was very controlled and allowed the rider to be super-aggressive without any question as to what the wheels were doing. The rear end also hooked up great. But ESP opted for stiffer springs, and the overall action was just too firm. The good news is the suspension mods would be even more reasonably priced with no spring changes required.As usual, Thumper put together a polished, complete and attractive off-road package. There is no useless bling. Essentially, it's just a purposeful off-road weapon with bigger muscles than before yet with a temperament as civilized as ever.