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TIT measurement vs 4 port EGT

Understanding AFR

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Hi All,

I have taken some EGT measurements on my 1.8L BP MX5 running a GTX2860 0.64 at 1 bar and it’s hard keeping turbine inlet below 900C on track (which is said to be the EGT limit for stock valves)

Though I’m not sure how temperature at the turbine inlet correlates to temperature in the usual 1-1.5x port diameters from the head. Does anyone have data for this?

thanks,

Tim

Hi Tim,

What lambda are you running to?

I’m away from my laptop at present but if someone hasn’t found you an answer in a week I shall see if I can do some math!

Hi Dave,

I've been running mainly at 0.75. I did try richer and it helped a little but not much. Going leaner made it hotter quickly.

Hey Tim,

0.75 is fairly rich so like you said leaning will make it start to heat up, the other thing you can do is to advance the timing, this moves where the peak cylinder pressure occurs meaning more of the combustion has taken place in the cylinder before the exhaust valve has opened reducing the temperature at the valve / seat. Of course when advancing the timing be monitoring knock and take precautions not to go into knock - when doing engine cal on a dyno the ignition is normally advance into knock and then 1.5-2 degrees removed to be in a safe area (again be careful)

Unfortunately like you said, this is where OEM parts will need to be replaced with more fit for purpose items and cylinder head work would most likely need to be done. Going to copper beryllium seats and guides for example. (Knights Engine Services near to Northampton are a fantastic machine shop for this kind of work)

Unfortunately I haven't worked the maths out but I have taken some screen shots of an F1 engine in GT Suite so you can see a thermal break down of the exhaust track. The exhaust port temps being right after the combustion event will be roughly ~150+ degrees C cooler than at the turbine intake as the rest of the cylinders will contribute to the rise in temperature at the turbine. With some of the energy removed as the air spins the turbo the temp is dropped slightly again at where the EGT would be measured post turbine.

I would ignore the exact temperatures in the screen shots but more look at the relationship between them. Also as reference, this example is at 4bar boost and 6000rpm where max power was seen for this particular set up, no where near to real life F1 specs.

*disclaimer - this is not a copy of any running F1 engine in use and is a model to studying turbo sizing done during my degree*

4bar_Turbo_Temp.png

4bar_Exhaust_temp.png