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A engine produces TQ. HP is a calculated figure based on rpm.

It all depends at what engine speed you will operate. In order to increase HP you need to increase the breathing ability of the engine, bigger ports, bigger valves, more cam, etc. Basically you have to make the engine able to rev sky high. The constant in the mathematic formula is 5252 (this is why at that rpm TQ and HP are always the same). If the engine is able to rev higher the rpm have a larger effect on the calculation then the TQ.

The more you increase all these things in order to gain HP on top, the more TQ you will lose on bottom.

Compare a VRod with a bagger, they have the HP but relatively puny TQ, put the VRod engine in a heavy bagger and it will fall on it's a$$ unless you constantly downshift to keep the engine in it's designed powerband.

On a old technology bike that is severely chassis limited TQ is the name of the game. It is not uncommon for a stock bike to pull a modified one on a top gear roll on for exactly this reason. A lot of guys that want big engines do not understand these basic facts and are unwilling to adjust their riding style.
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