Turbocharger lag is attributed to which factor by Technician A in the discussion?

• A. The inertia of heavy compressor and turbine wheel assemblies
• B. The slow buildup of fuel rate by the high-pressure injection system
• C. Both factors equally contribute
• D. Neither factor contributes significantly

Answer: (A)

Turbocharger lag mainly comes from the inertia of the rotating turbo hardware. When you open the throttle, exhaust gas must spin up the turbine, which in turn drives the compressor to pressurize intake air. Those wheels are relatively heavy, so they resist rapid acceleration. It takes some time for the turbine to reach operating speed and for the compressor to build boost, which is what you feel as lag. The fuel system’s response matters for how quickly the engine can use the boosted air, but the initial delay in creating boost is dominated by the rotating mass of the compressor and turbine. That’s why attributing lag to the inertia of those assemblies is the best explanation.