Glossary¶
Quick definitions for the abbreviations and terms used across the wiki.
| Term | Stands for | Meaning |
|---|---|---|
| λ (lambda) | — | Actual air–fuel ratio ÷ stoichiometric. λ=1 stoich, <1 rich, >1 lean. See Air–Fuel Ratio. |
| AFR | Air–Fuel Ratio | Mass of air per mass of fuel (≈14.7:1 stoich for petrol). |
| VE | Volumetric Efficiency | How completely the cylinder fills with air vs theoretical max. See VE Table. |
| MAP | Manifold Absolute Pressure | Intake manifold pressure (kPa); the primary load signal. See MAP. |
| IAT | Intake Air Temperature | Temperature of incoming air; sets charge density. See IAT. |
| ECT / CLT | Engine Coolant Temp / Coolant Temp | Engine temperature; drives enrichment, idle, knock. See CLT. |
| TPS | Throttle Position Sensor | Throttle opening / driver demand, 0–1. See TPS. |
| BTDC | Before Top Dead Center | Crank angle ahead of TDC where the spark fires. See Timing Table. |
| TDC | Top Dead Center | Piston at the very top of its stroke. |
| MBT | Minimum advance for Best Torque | The spark timing that makes the most torque. See Spark Fundamentals. |
| LSA | Lobe Separation Angle | Camshaft spec governing valve overlap. See Camshaft. |
| VVT | Variable Valve Timing | Cam timing that shifts with RPM to widen the power band. |
| DFCO | Decel Fuel Cut-Off | Fuel cut on closed throttle at speed. See DFCO. |
| STFT | Short-Term Fuel Trim | The closed-loop correction toward target λ (±25%). See Closed-Loop. |
| RON | Research Octane Number | A fuel's resistance to knock. See Octane. |
| Knock | Detonation | Uncontrolled end-gas auto-ignition; damaging. See Knock. |
| Speed-density | — | Air-mass estimation from RPM, MAP, temperature, and VE. See Speed-Density. |
| Stoichiometric | — | The air–fuel ratio that burns with nothing left over (λ=1). |
| Wall-wetting | — | Fuel condensing on cold intake walls; the reason for enrichment. See Enrichment. |
| Wall film | — | The liquid fuel puddle on the intake-port walls that evaporates back into the airflow. See Wall-Film Compensation. |
| X–τ (x-tau) | — | The classic wall-film model: X is the fraction of injected fuel that goes into the film, τ (tau) is how slowly it evaporates. See Wall-Film Compensation. |
| Duty cycle | — | Fraction of each cycle an injector is open; the maximum (typically 85%) is its ceiling. See Injectors. |
| Dead time | — | An injector's minimum pulse width; the ECU compensates for it. See Injectors. |
| Dashpot | — | Eases the throttle closed after a blip so RPM doesn't dip or stall. See Idle Control. |
| Scavenging | — | Using exhaust pulses to help clear and fill the cylinder. See Exhaust Header. |
| Dyno excitation | — | The brake load you set in Manual dyno mode, 0–100 %; more excitation, more load. See Dyno. |
| Plug wetness / Flooding | — | Running far too rich at low RPM wets the plugs so the engine won't fire; the state window shows FLOODED. See Cranking Enrichment. |
| Catalyst | Catalytic converter | An exhaust part that burns small amounts of unburnt fuel — which is why stock cars don't pop. See Exhaust Pops & Afterfire. |
| Afterfire | — | Unburnt fuel igniting in the hot exhaust, heard as a bang or burble. See Exhaust Pops & Afterfire. |
| Limp mode | — | A damaged-engine state with RPM capped at 3000 and the throttle clamped to 50 %. See Damage & Wear. |
| Bulb check | — | All eight warning lights coming on together when the ignition is on and the engine isn't running. See Warning Lights. |