So a BTT and a Legend 4 are nearly identical engines, they have the same piston and sleeve but have different crankshafts... The Legend 4 has a onroad style crank with a large bore and double tungsten slugs whereas the BTT has a offroad crank with a smaller bore and no slugs..... Sometime in the next little bit I plan to dyno test my Legend 4 and will swap back and forth between a BTT and Legend crank to see what the difference is....generally speaking the larger bore crank has a smoother throttle response but makes more power and RPM...but usually a crank like that is in a engine with higher timing and more aggressive porting, so we will see what the results are...