Glossary / Knowledge Base / Mazda MX-5 NC

A

AFR Fueling

Air-Fuel Ratio. For petrol, stoich is 14.7:1. Lambda × 14.7 = AFR. WOT targets depend on NA/turbo & fuel.

AAT/IAT Temps

Intake Air Temperature. Higher IAT raises knock risk, reduces timing and power. Manage with intercooler and airflow.

Advance (Ignition) Ignition

Degrees BTDC. More advance until knock or MBT; tune by logs and dyno, not by hearsay.

B

Boost / MAP Boost

Pressure above atmospheric measured in the manifold. Clean rise + slight taper is normal; oscillation = control issue.

BSFC Fueling

Brake Specific Fuel Consumption (lb/hp/hr). Rules of thumb: NA ~0.50–0.55, Turbo ~0.60–0.70, E85 ~0.70–0.80.

Duty Cycle (Boost) Boost

% time a solenoid is energized in a cycle. Higher duty generally increases boost until mechanical limits.

C

Closed-Loop / Open-Loop ECU

Closed-loop uses O2 feedback (cruise/idle). Open-loop ignores it (WOT), relying on maps.

Compressor Map Turbo

Turbo chart showing flow vs pressure ratio and efficiency. Avoid surge (left) and choke (right) regions.

CEL / DTC Diagnostics

Check Engine Light / Diagnostic Trouble Code. Always read codes before guessing.

D

DFCO ECU

Decel Fuel Cut-Off. ECU cuts fuel on overrun to save fuel and cool exhaust.

Dwell Ignition

Time the coil charges before firing. Too high overheats coils; too low weak spark.

Dyno Correction / Smoothing Dyno

Standards (SAE/DIN) normalize for weather; smoothing removes noise. Keep consistent for comparisons.

E

ECT Temps

Engine Coolant Temperature. Rising ECT shifts knock threshold and can trigger protection.

E85 / Flex Fuel Fueling

High-ethanol fuel resists knock but needs ~30% more flow. Flex sensor enables blend-based maps.

EGT Temps

Exhaust Gas Temperature. Useful indicator of timing, fueling, and turbo stress under load.

F

Fuel Trims (STFT/LTFT) ECU

Short/Long-Term corrections. Healthy cruise typically within ±5–10% once tuned and leak-free.

Fuel Cut / Boost Cut Safety

ECU protections that limit fuel or throttle when unsafe mass air/boost conditions occur.

G

Gain (Boost Control) Boost

Controller aggressiveness versus target error. Too high = oscillation; too low = lazy response.

GDI / Port Injection Fueling

Direct vs manifold fuel delivery. NC is port injection; DI needs different sizing and pressure logic.

H

Heat Soak Temps

When components heat up run-to-run, raising IAT/ECT and reducing repeatability and power.

Horsepower (whp/bhp) Dyno

Engine work rate. Wheel HP (dyno) differs from brake HP (engine); compare consistently.

I

Idle Control ECU

ECU strategy holding idle speed via air/fuel/spark. Cammed engines need different targets.

IDC Fueling

Injector Duty Cycle. Sustained 95–100% = out of headroom; upgrade injectors/pump.

K

Knock Ignition

Abnormal combustion. Managed by octane, IAT/ECT, AFR, and timing. Always log knock activity.

L

Lambda Fueling

Normalized AFR (1.0 = stoich). Universal across fuels; Lambda × stoich AFR = actual AFR.

Load ECU

ECU’s estimate of air mass (via MAF or MAP/VE). Drives timing/fueling targets.

M

MAF ECU

Mass Air Flow sensor. Housing diameter and placement require proper scaling in the tune.

MAP Sensor Boost

Manifold Absolute Pressure. Stock NC ~1.5 bar abs; upgrade to 3 bar for higher boost and rescale.

MBT Ignition

Minimum spark for best torque. Limited by knock; tune toward MBT where knock allows.

N

NA Engine

Naturally Aspirated (no forced induction). Needs volumetric efficiency to make power.

O

O₂ Sensor Sensors

Measures exhaust oxygen. Narrowband for closed-loop; wideband for tuning WOT.

Overrun / Pop-&-Bang ECU

Fuel/spark strategies on throttle lift. Fun, but hard on cats/turbos; use sparingly.

P

PID Control Control

Proportional/Integral/Derivative logic for boost and idle control. Balance response vs stability.

Pump Flow (LPH) Fueling

Fuel pump capacity in liters/hour at pressure. Flow drops as pressure/voltage rise/fall.

R

Rev Limit ECU

Maximum engine speed. Soft cut is gentler; hard cut is abrupt. Don’t raise without valve-train proof.

Rich / Lean Fueling

Rich = more fuel than stoich; Lean = less. Tune WOT richer for cooling/safety.

S

Speed-Density (SD) ECU

Fueling via MAP, IAT, and VE table instead of MAF. Needs accurate VE model and sensor scaling.

STFT ECU

Short-Term Fuel Trim. Rapid corrections the ECU makes in closed-loop operation.

Spool Turbo

Time/engine speed required for the turbo to reach target boost. Affected by turbine A/R, exhaust, and tuning.

T

Timing (Ignition) Ignition

When the spark fires relative to piston position. Balance between MBT and knock limits.

LTFT ECU

Long-Term Fuel Trim. Learned corrections over time; big values indicate underlying issues.

Turbo Blanket Turbo

Insulation for hot side to reduce bay temps and maintain turbine energy. Watch for oil line proximity.

V

VCT Cams

Variable Cam Timing. Adjusts cam phasing for torque/power/emissions; needs retuning on swaps/cams.

VE Engine

Volumetric Efficiency — how well the engine breathes versus displacement. Core to SD tuning.

W

WOT Driving

Wide Open Throttle. Tune and log here for safe targets; verify repeatability on dyno and road.

Wideband Sensors

AFR sensor with broad range for tuning. Place pre-cat for accuracy, manage heat and sealing.