While the CRF450R and the TRX450R share the same displacement number, there are very few of the same components between the two engines. Initially, many people were disappointed because the first TRX450R was very weak compared to the CRF450R. Honda claims that it designed the TRX450R engine to produce more torque so that the engine was more suited for ATV purposes. In 2004 and 2005, the only interchangeable part between the ATV and motorcycle engines was the camshaft. In 2006, Honda overhauled the TRX450R engine to make it more similar to its motorcycle variant. This included a more aggressive cam profile, a larger bore with a shortened stroke, a new, short skirt piston and titanium rather than steel valves. In addition, Honda changed the carburetor from a 42 mm Keihin butterfly type to a 40 mm Keihin FCR. This increased the power from about 33 horsepower (25 kW) in the first generation to over 40 horsepower (30 kW) in the second. The first generation engine had a 10.5:1 compression ratio while the second generation had a 12:1 compression ratio.
wikipedia was the source... any help?