Low boost can be caused by excessive bearing drag.

Low boost can be caused by excessive bearing drag.

• A. Bearing drag
• B. Not sure
• C. False
• D. True

Answer: (D)

Boost pressure in a turbocharged system depends on how freely the turbo can spin. Excessive bearing drag inside the turbine/compressor assembly creates a bigger parasitic load, so more of the shaft power goes into overcoming friction rather than accelerating the compressor. That means the turbo spins up more slowly and cannot reach the same speed or pressure ratio, especially under load, which shows up as lower-than-expected boost. So the statement is true: bearing drag can cause low boost. Issues that raise bearing drag include poor lubrication, worn or damaged bearings, contaminated oil, or incorrect oil viscosity, all of which increase friction and hinder boost.

Boost pressure in a turbocharged system depends on how freely the turbo can spin. Excessive bearing drag inside the turbine/compressor assembly creates a bigger parasitic load, so more of the shaft power goes into overcoming friction rather than accelerating the compressor. That means the turbo spins up more slowly and cannot reach the same speed or pressure ratio, especially under load, which shows up as lower-than-expected boost. So the statement is true: bearing drag can cause low boost. Issues that raise bearing drag include poor lubrication, worn or damaged bearings, contaminated oil, or incorrect oil viscosity, all of which increase friction and hinder boost.