The Big Problem With Modern Manual Transmissions - Rev Hang

Summary by Krater

This video explains the differences between mechanical and electronic throttle bodies, focusing on why electronic throttles cause rev hang in manual transmission vehicles, and how delayed throttle closure and port injection wall wetting contribute to hydrocarbon emissions.

From the video

Answers: What causes rev hang in manual transmission cars with electronic throttle bodies?

• Mechanical vs electronic throttle bodies
• Throttle response curves
• RPM dependent torque
• Catalytic converter air-fuel ratio sensitivity
• Throttle tip-in and tip-out
• Rev hang causes and solutions
• Port injection wall wetting

What it concludes

• Electronic throttles can improve pedal feel by linearizing the torque response curve relative to accelerator pedal position.
• Rich air-fuel ratios increase carbon monoxide and hydrocarbon emissions, while lean ratios increase nitrogen oxide emissions.
• Throttle tip-in and tip-out cause transient air-fuel ratio variances leading to poor emissions.
• Rev hang is caused by electronic throttles slowly closing the throttle valve and delaying fuel cut-off during gear shifts to burn remaining fuel on intake port walls and reduce hydrocarbon emissions.
• Direct injection avoids the port injection wall wetting problem and associated rev hang issues.