Tuning Glossary: Plain-English Definitions

The words

ECU (engine control unit) The computer that runs your engine. It reads sensors and decides how much fuel, air and spark the engine gets.

TCU (transmission control unit) The computer that runs your automatic or dual-clutch gearbox. It decides when and how the car shifts.

Calibration, map, file or tune All mean roughly the same thing: the set of instructions and limits stored in the ECU or TCU. "Tuning" means changing them.

Stock file The original factory calibration your car came with. "Returning to stock" means putting that original software back.

Custom tune A calibration built for your specific car, parts, fuel and driving, rather than a generic file made for every car of that model.

Off-the-shelf file (generic or "canned" tune) A calibration written once for a model and loaded onto many cars without being adjusted for each one.

Stage 1, 2, 3 Shorthand for how far a car has been modified. Stage 1 is usually tune only, Stage 2 adds bolt-on parts, and Stage 3 usually means bigger hardware. It varies by car.

Horsepower (HP) A measure of how much work the engine can do over time. It mostly shows up as top-end speed and how hard the car pulls at higher engine speeds.

Torque The twisting force the engine produces. It is what you feel as the shove in your back when you accelerate, especially from lower engine speeds. Often written as ft-lbs (foot-pounds).

Crank horsepower Power measured at the engine itself. Manufacturers usually quote this number.

WHP (wheel horsepower) Power measured at the wheels, usually on a dyno. It is lower than crank horsepower, because some power is lost through the gearbox, driveshafts and axles on the way to the wheels.

Dyno (dynamometer) A machine that measures a car's power and torque. The car is strapped down and driven on rollers. Different dyno brands can read differently, so numbers are best compared on the same machine.

Turbo (turbocharger) A fan spun by the engine's exhaust gas. It pushes extra air into the engine, which lets it burn more fuel and make more power.

Boost The extra air pressure a turbo pushes into the engine. Turning up boost is one of the main ways a tune adds power to a turbocharged car.

Intercooler A radiator for the air coming out of the turbo. Squeezing air makes it hot, and the intercooler cools it before it enters the engine. Cooler air is denser and lowers the risk of knock.

Intake The pipe and filter that bring air into the engine. Aftermarket intakes are designed to let air flow in more easily.

Downpipe The section of exhaust pipe that bolts on right after the turbo. Aftermarket downpipes let exhaust flow out more easily. Many change or remove emissions parts and are meant for off-road or track use only.

Knock (detonation) When fuel in a cylinder burns unevenly and too early, instead of in a smooth, controlled way. It can sound like a light pinging or rattling. Heavy knock can damage an engine. Knock sensors listen for it, and the ECU backs off to protect the engine.

Ignition timing When the spark plug fires. Small changes in timing affect power and the risk of knock.

Octane A rating of how well fuel resists knock. Higher octane fuel, like premium, resists knock better. It does not contain more energy, it just lets a tune safely ask more of the engine.

E85 A fuel blend that is mostly ethanol (an alcohol made mainly from corn in the US) mixed with gasoline. Despite the name, it contains anywhere from 51% to 83% ethanol depending on season and region. It resists knock very well, but you get fewer miles per gallon.

Flex fuel A setup that lets a car run on gasoline, E85 or any mix of the two. A sensor measures the ethanol content in the tank, and the tune adjusts automatically.

Ethanol content sensor (flex fuel sensor) The sensor in a flex fuel kit that measures how much ethanol is in the fuel and tells the ECU in real time.

Data log A recording of what the engine is doing while the car is driven, like boost, timing and temperatures. Tuners use logs to check and fine-tune a calibration.

Direct injection An engine design that sprays fuel straight into the cylinder. It is efficient but can lead to carbon buildup on the intake valves over time.

Walnut blasting A way to clean carbon off the intake valves of a direct injection engine by blowing crushed walnut shells at them.

Platform A family of cars that share the same engine, gearbox and computers. Tuning advice is usually given per platform.

Pre-purchase inspection A check of a used car before you buy it, so you know its condition and any problems up front.

Have a question about a word on your quote? Send it to us with your car details and we will explain.