Heat: IAT, EGT, coolant and protection

Heat is the common currency of engine damage. The trims and protection tables exist to spend less of it.

Intake air temperature

Hot intake air is less dense (less power) and lowers the knock limit. The IAT timing trim pulls advance as the air heats up. Heat soak after a pull raises IAT for minutes: compare runs with similar start IAT, and cool down between pulls.

Exhaust gas temperature

EGT rises with load and rpm, with lean mixtures (more oxygen left to burn, less fuel to cool), and with late combustion — retarded or knock-pulled timing burns the charge in the exhaust instead of the cylinder. Around 950 °C exhaust valves and turbine wheels start to suffer. EGT protection enrichment richens the final λ target as EGT climbs: it is why factory maps run rich at sustained load.

Coolant temperature

A hot engine knocks sooner. The ECT timing trim pulls advance above ~95 °C. Past ~112 °C the head gasket is at risk. Long steady-state sessions in a poorly cooled cell get there.

Piston crown

The crown temperature you cannot see is set by load, mixture and knock. Lean under boost is the fast way to melt one; detonation is the fast way to break one. Oil squirters and forged alloys raise the limit without removing it.

Knowing your thresholds

In this app the numbers are not a secret: open "Limits for this build" in the Health panel and it lists, for the parts currently fitted, where each component starts to take damage: EGT for the valves and the turbine, shaft speed for the turbo, cylinder pressure for the rods and the head gasket, crown temperature for the pistons, coolant temperature, valve float. Forged internals, stiffer springs and a different turbo move them, so read it again after a change of parts.

• Which gauges show them: EGT, coolant, IAT and turbo speed are on the gauges and in the logs. Piston crown and cylinder pressure are X-Ray channels; in real life you infer them from EGT, λ and knock, which is why those three are watched so closely.
• Margin, not the number: damage grows with how far and how long a limit is exceeded, and a hot day or a heat-soaked pull adds 20–30 °C of EGT on its own. Tune to about 25 °C under the EGT limit, 10 bar under the pressure limit and 500 rpm under valve float, on a cooled pull.
• Protection is a threshold too: the EGT protection table starts richening 100 °C before the valves suffer. If it is active on every pull, you are tuning in the margin, not under it.

In real life the thresholds come from the parts: the turbo maker's turbine inlet temperature limit (roughly 950 °C for common turbine alloys, higher for Inconel wheels), the piston alloy and whether the crowns are oil-cooled, the valve material, the rod and bolt rating, and the coolant system's design temperature. Two cautions that the app spares you: an EGT probe after the turbine reads 100–150 °C lower than one before it, so a limit only means something with the probe location stated, and a single-cylinder probe hides the hottest cylinder. Experienced tuners treat EGT as a trend against a known-good baseline on the same car and the same probe, and keep the hard limits for what they are: the point at which parts are already being consumed.