A
- AFR
- Air-Fuel Ratio. 14.7:1 is stoichiometric for gasoline. Tuned cars target ~11.5–12.5:1 under boost for safety.
- Anti-lag
- System that keeps turbos spinning off-throttle by retarding ignition or injecting extra fuel into the exhaust. Hard on hardware.
B
- Boost
- Manifold pressure above atmospheric, measured in psi or bar. Stock S58 runs ~16 psi; Stage 2 pushes ~22+ psi.
C
- Catless
- Downpipe with no catalytic converter. Improves flow and turbo response, but illegal for street use in most regions.
- Closed-loop
- ECU mode where fuel trims are corrected in real time using O2 feedback. Open-loop happens at WOT on most platforms.
D
- DME
- Digital Motor Electronics — BMW's name for the ECU.
- Downpipe
- Exhaust section directly after the turbo. Catless or high-flow versions reduce backpressure significantly.
- DPF
- Diesel Particulate Filter. Captures soot; removal is common on tuned diesels but illegal in most regions.
E
- ECU
- Engine Control Unit. The computer that runs your engine.
- EGR
- Exhaust Gas Recirculation. Reroutes exhaust into the intake to lower NOx; often disabled on performance tunes.
F
- Flash
- Writing a new calibration file to the ECU via OBD or bench. This is done by your tuner with their own tool — TuneAI never flashes anything.
- Flex Fuel
- System that detects ethanol content and adjusts the tune dynamically. E30–E85 unlocks massive gains over pump.
H
- HPFP
- High-Pressure Fuel Pump. Direct injection systems live or die by pump capacity — often the limit on big builds.
I
- IAT
- Intake Air Temperature. Hotter air = less timing, less power. Watch IAT under sustained WOT.
K
- Knock
- Uncontrolled detonation. Damaging. Modern ECUs retard timing automatically when knock is detected.
L
- Lambda
- AFR expressed as ratio to stoich. 1.0 lambda = 14.7:1 AFR. Tuners target ~0.78–0.85 lambda under boost.
M
- MAF
- Mass Air Flow sensor. Measures intake air mass. BMW moved to MAP-based systems in modern cars.
- Map
- A 2D or 3D table inside the ECU (e.g. ignition vs RPM vs load). Tuning = editing maps.
- MAP
- Manifold Absolute Pressure sensor. Reads boost; the foundation of speed-density tuning.
- Methanol
- Liquid injected into the intake to cool charge air and add octane. Effective and cheap; risk of failure if pump dies.
O
- OBD
- On-Board Diagnostics port. The standard interface for reading codes and flashing the ECU.
P
- PID
- Parameter ID. A specific live data stream from the ECU (e.g. boost, AFR, IAT).
T
- TCU
- Transmission Control Unit. AMG TCT and ZF 8HP both benefit massively from TCU recalibration.
V
- VANOS
- BMW's variable valve timing system.
W
- Wastegate
- Valve that bleeds exhaust around the turbo to control boost. Internal (built-in) or external.
- WGDC
- Wastegate Duty Cycle. The % of time the ECU commands the wastegate closed. Critical PID for boost control diagnosis.