Engine & Valvetrain
RPO
GM Regular Production Option code. On LS-era engines it is one of the fastest ways to distinguish variants such as LM7, LQ4, LY6 or L96.
AFM / DOD
Active Fuel Management / Displacement on Demand. Cylinder-deactivation hardware and calibration used on selected Gen IV applications.
VVT
Variable Valve Timing. Changes cam phasing while the engine runs. A VVT engine can be kept functional, limited, or converted to fixed timing depending on the build.
24x / 58x
Crankshaft reluctor signal families. They affect crank sensing, ECM compatibility and swap wiring; do not select an ECM/harness without knowing which signal family the engine uses.
Cathedral / Rectangle Port
Common intake-port families. The intake manifold must match the cylinder-head port/bolt arrangement.
LSA
Lobe Separation Angle. The angular separation between intake and exhaust lobe centerlines; one influence on overlap and idle/powerband character.
Tuning & Datalogging
STFT / LTFT
Short-Term and Long-Term Fuel Trim. PCM corrections used in closed loop; useful context for part-throttle fueling and diagnosing air/fuel delivery issues.
KR
Knock Retard. Timing the controller removes in response to knock strategy. A logged KR event should be interpreted with rpm, load, spark, fuel and mechanical context.
Lambda
Air/fuel ratio normalized to stoichiometric. Lambda 1.00 is stoich for the fuel in use, making lambda easier than raw AFR when switching gasoline/ethanol blends.
MAF / VE
Mass Air Flow and volumetric-efficiency modeling are two major ways GM controllers estimate cylinder airflow/load, depending on operating mode and calibration.
Transmission
TCC
Torque Converter Clutch. Locks the converter to reduce slip/heat and change driveline behavior.
Slip RPM
The difference between engine speed and the theoretical input/output relationship. Context matters: an unlocked converter is expected to slip; a locked clutch should behave differently.
Torque Management
Engine/transmission control strategies that reduce delivered torque during shifts or protection events. Removing all of it is not automatically a performance improvement.