How much horsepower does a turbocharger use from diesel engine?

A turbocharger doesn't *use* horsepower from the diesel engine in the sense of consuming it. Instead, it uses a portion of the engine's exhaust gas energy to drive the turbine, which in turn compresses the incoming air. This increases the engine's power output significantly more than the energy "lost" to driving the turbo.

The amount of energy taken from the exhaust gas is relatively small compared to the overall power produced by the engine. There's no fixed percentage; it varies depending on factors like engine design, turbocharger size and efficiency, and operating conditions (engine speed and load). Think of it as a parasitic loss – a small reduction in the potential power that could be delivered to the wheels if the turbo wasn't there – but one far outweighed by the gains in power from the forced induction. Generally, the power increase from a turbocharger greatly surpasses the power "lost" driving it.