IAT settings explanation from Link ECU

[Warchild]

Good day 

In the Linkecu manual, it states the following regarding the IAT Fuel corrections:

"Ideally, the correction at 20 degrees Celsius , correction should be set to zero. Positive correction BELOW 20 degrees Celsius must be set to ENRICH, air temperatures ABOVE 20 degrees Celsius must be set to NEGATIVE values to reduce fuel delivery"

Surely this can't be right ? If I have a car running on the track with let's say 40-50 degrees intake air temperatures, surely you have increased knock possibility, due to warmer intake temperatures, and should add MORE fuel to cool the intake temperatures ? This makes no sense to me ? Please explain ?

[Adamw]

The general aim of tuning is to achieve a consistent air-fuel ratio.  Air, like any gas gets less dense as temperature increases, this means there is less air mass inside the combustion chamber.  Therefore to keep the air fuel ratio on target if you have less air mass in the cylinder, you need to inject less fuel mass.   This density effect is generally described by "Boyle's law" or "Ideal gas law".  A rough rule of thumb is air gets about 4% less dense for every 10°C increase in temp - so it is quite significant.  You could for example compromise and pull out only 2% for every 10deg, and it would still get richer as temp increased.  

If you are knock limited and cannot control air temperatures then sure you can try running richer to aid cooling - but to reduce susceptibility to knock you are probably better to remove timing when IAT gets too high, on piston engines adding fuel generally doesnt suppress knock much.  Water injection is another common option.  

[Warchild]

Ok thank you very much , makes perfect sense now !