RU's info on temp Vs. ignition timing.

We advance the spark, the combustion occurs earlier so more work is done on the piston = more power. Since the amount of energy in one chamber full is constant, the more work we do on the piston the less gets passed out the exhaust port so the EGT is LOWER for a more advanced spark.

Retarding the spark, means combustion occurs later so less work at the psiton (less power) plus more wasted energy = higher EGT.

This can be used to give more boost but if youaren't transferring the results to the piston then the engine runs less efficiently. Since we have to keep things cool to prevent cracking we actually end up running too rich to cool things down again.

All this torque of optimum fuelling EGT is nonsense. A turbo engine will be run far richer than optimum (approx 5%CO 0.85 Lambda) in order to keep things cool.

Remember kids you're calibrating to optmum TORQUE not EGT. EGT is only an indicator and a limit.

Hard limits to tuning a turbo engine?

1) Knock
2) EGT limit
3) Max cylinder pressure
4) Compressor shaft speed
5) Ignition limit

In practice you keep reatarding the spark as you increase pressure until you can't add enough fuel it keep it cool. At that point, you either reduce compression ratio, reduce restrictions, add RON or add cooling.
4)

Let me clarify a few things: advancing the spark increases the temperature in the combustion chamber but as this results in increased work done on the piston plus more heat transfer throught the walls, the end result is that the EGT is cooler after the exhaust valve opens.

Det is a result of pressure/temperature in the charge plus the surface temperature of the combustion chamber hence advancing spark increases tendency to det. Some fuels will det less than others irrespective of detonation: eg Elf Turbomax is only just over 100 RON but lets you run a WRC car a 2bar boost against 11:1 compression w/o det.

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Cheers,

Ruaraidh