T3/T4 hybrid turbocharger assembly is created by installing a T4 compressor wheel and housing onto a T3 turbine housing wheel and center section. A T3/T4 hybrid turbocharger assembly is a compromise for engines where a T3 turbocharger is too small to reach the desired maximum horsepower but using a T4 turbocharger would create an unacceptable amount of turbo lag. The T3/T4 turbocharger is designed to be used on engines displacing 1.5L-3.0L and is typically good for around 400HP. They are also commonly used in twin turbo applications. In this case those figures would be doubled 3.2L-5.0L engines up to 800HP. Horsepower ratings are generally meant to express the turbochargers maximum airflow capability. Recommended boost pressures are 7psi(0.5 Bar) to 21psi(1.5 Bar) and boost pressures should not exceed 30psi(2 Bar). Exceeding 21psi(1.5 Bar) of boost pressure can significantly reduce a turbochargers lifespan. Generally speaking 14psi(1 Bar) is good for a 100% increase in horsepower from a naturally aspirated engine. Also factory non-turbo engines without forged internal components on high octane pump gas (91-92 octane) it is not recommended exceeding 7psi (.5 Bar) of boost. Doing so could result in damaging your engine.