Charge temp correction

[Julien]

Hi guys,

There is something I don’t get in the help file.

It says that the values should be adjusted during cold start but since the table is based on speed/mgp I would have only worked it at operating temp as far as the ECT is concerned.

[Adamw]

You generally have to check it at various loads and RPM's, I normally do abot 4 or 6 points to get an idea of the trend and extrapolate from there. 

To confirm the value you really need to isolate IAT & ECT effects - what I usually do is hold at steady state on the dyno with ECT relatively stable, then block airflow to the intercooler with a piece of cardboard or similar so the IAT increases quickly while ECT doesnt.  If it goes lean as IAT heats up then it needs a larger value.   

[Julien]

Yes that makes full sense to me but you only do it with the EC at operating temp.

you don’t try to extrapolate the values during warmups ?

[Adamw]

What the charge temp table is trying to approximate is the temperature of the air/fuel mix as it enters the combustion chamber.  The air is first measured by the IAT as it enters the manifold, then it absorbs heat from the manifold walls, port walls and back of the intake valve as it moves through the system towards the combustion chamber.  The amount of heat it picks up varies with how much air is flowing, the faster it moves the less heat it picks up.  For this reason the table usually references RPM & load as that is a good indicator of airflow.

A value of 0 in the charge temp table means the air picked up no heat from the port walls etc and is still at the IAT we measured in the manifold when it enters the chamber.  A value of 100% in the table means the air entering the combustion chamber has equalised with the port temperature so we assume the charge temp matches the coolant temp (port walls and manifold walls are somewhere close to coolant temp). 

To work out how much effect coolant temp and air temp is having on the temp of the charge reaching the chamber we really need to isolate one of those variables.  It could be you vary coolant temp while keeping IAT constant (usually more difficult), or you vary air temp while keeping engine temp constant.  Sometimes you can do this by temporarily ducting hot air into the intake from a hot area or block the intercooler.  

You could use a cold start/warmup cycle as typically the coolant changes a lot more than the IAT during a warm up, but there are also other factors going during warmup such as more fuel condensing on the port walls etc that will likely bias results a bit.  

 

  

[Julien]

All clear for thermodynamic aspects and the purpose of this correction. I’ll do as you suggest with a cardboard on the air/air cooler.

it’s just your manual that says to do it also during warming up that I wanted to clarify. You confirm what I had in mind, it’s only a relatively short phase with many other adjustments so I’ll only work this table once the engine is at operating temp.