Tuning glossary

The mass ratio of air to fuel in the combustion charge, the core metric you tune fueling against.

The intake manifold pressure above atmospheric created by a turbo or supercharger, usually measured in psi.

The most spark advance the engine can run at a given point before knock begins.

Brake Specific Fuel Consumption, the fuel an engine burns per unit of power, used to size injectors.

The complete set of editable ECU tables and parameters that control how the engine runs.

Two fueling modes: closed loop corrects fuel from O2 feedback, open loop runs the commanded value blind.

A time-series recording of engine sensor and ECU parameters captured during driving, used to diagnose and refine a tune.

The effective altitude the engine experiences once temperature, pressure, and humidity are combined, driving how much air is actually available.

Uncontrolled secondary auto-ignition of the end gas after the spark, producing a sharp knock.

A dynamometer that measures an engine's power and torque under controlled load for tuning and validation.

Remote tuning where you send datalogs to a tuner who returns revised calibration files by email.

Writing a modified calibration into the ECU/PCM's memory, replacing the existing tune with your new one.

The real cylinder compression once boost is added to the static mechanical ratio, the true predictor of detonation risk under boost.

The ECU's percentage corrections to fueling based on oxygen sensor feedback, short-term and long-term.

The gradual rise in intake and component temperatures during repeated or sustained load that erodes power and safety margin.

A VCM Scanner analysis tool that bins logged data into a table-shaped grid (matching a tune table's axes) and averages each cell.

The licensing currency HP Tuners charges to unlock a specific vehicle (VIN) for tuning on your interface.

The pulse width where injector flow transitions from the low-slope region to the high-slope region.

The percentage of available time an injector is held open, indicating how close it is to maxing out.

The latency between the ECU commanding an injector open and it actually delivering fuel, varying with voltage.

The flow rate of an injector in mass per millisecond of open time, with separate high and low pressure regions.

The temperature of air entering the engine, used to correct air-density calculations and trigger heat-related timing and fuel adjustments.

A heat exchanger that cools compressed intake air after the turbo or supercharger to make it denser and reduce knock.

Timing the ECU automatically pulls when its knock sensors detect detonation.

A normalized air-fuel ratio where 1.0 is stoichiometric regardless of fuel type.

The condition where airflow exceeds the MAF sensor's measurable range, capping its signal and starving the PCM of accurate airflow data.

The calibration table that converts the MAF sensor's raw signal (frequency or voltage) into an actual airflow value in grams per second.

A sensor reading of absolute pressure inside the intake manifold, used as a load input and the key variable in speed-density airflow math.

A sensor that directly measures the mass of air entering the engine, used as the primary airflow input for fueling.

The minimum spark advance that produces maximum brake torque at a given operating point.

The HP Tuners hardware device that plugs into the OBD-II port and bridges your laptop to the vehicle's ECU for reading, writing, and logging.

The factory oxygen sensor that only reads accurately right at stoichiometric, used by the ECU for closed-loop fuel trims.

A fuel's resistance to auto-ignition, which sets how much timing and boost it can support.

An identifier for a single live data channel (a sensor reading or computed value) that VCM Scanner can request and log from the ECU.

The open-loop mode that commands a richer AFR under high load to make power and protect the engine.

Ignition of the charge before the spark fires, caused by a hot surface in the chamber.

The ratio of absolute outlet pressure to absolute inlet pressure across a compressor, used to place an operating point on the compressor map.

How many crank degrees before top dead center the spark plug fires.

An airflow-estimation strategy that calculates intake air mass from RPM, manifold pressure, and air temperature instead of measuring it directly.

The exact air-fuel mix for complete combustion with no leftover fuel or oxygen.

HP Tuners' desktop application for reading, modifying, and writing the tune file (calibration) stored in your vehicle's ECU/PCM.

HP Tuners' data-logging application that records live sensor and PID data from the vehicle so you can validate and refine a tune.

Tying your HP Tuners interface to a specific vehicle's VIN, using credits, so you're permitted to write tunes to that vehicle.

A measure of how effectively the engine fills its cylinders with air, used by the speed-density model to estimate airflow.

A valve that diverts exhaust around the turbine to cap how much boost a turbocharger can build.

A precision oxygen sensor that measures actual air-fuel ratio across a broad range, used to verify and dial in fueling.