The two new bikes have the motocrosser’s engine, but each off-road model gets its own unique tune, presumably with the FX being more aggressive than the WR. The FX engine is tunable with the GYTR Power Tuner, but the WR engine is not in stock form.
The off-road models each get a wide ratio transmission (a 5-speed, just like the MXer) and a different clutch (compared to the MX bike) with different fiber material, a judder spring, lighter clutch springs, and a different clutch actuator arm with a different cam on it. (Presumably all the mods are for a lighter clutch with a less-abrupt engagement, but Yamaha would not confirm this). The WR also gets an o-ring chain.
Both bikes also get revised engine mounts, as well as a ‘large capacity generator.’ They both swap their 19” rear wheel for an 18” rear, and in 2016 each of the 450 Yamahas comes with different tires. While the MXer comes with Dunlop MX52 tires, the WR comes with MX51s, and the FX gets Dunlop AT81s.
Only the WR is CARB/EPA legal, so it gets a green sticker in California. While the closed-course only FX keeps the YZF’s same exhaust, the WR gets something very different; the WR’s muffler/spark arrestor is a mechanical design (baffles rather than packing material). Along with this muffler/spark arrestor, only the WR gets a throttle stop and a resonator in the airbox. Other mods that the WR only gets are a headlight and taillight, an enduro computer, and a radiator fan.