MAT Air density table

[maych87]

My car gets very heat soaked. I have moved the location of the ait sensor, made the intake pipe out of fiberglass to replace the metal intake and wraped the intake in heat protective wrap. It has gotten a bit better. I think the rest of the high ait is the air temp in the engine bay. I will install a fan eventual to try to get more heat out of the engine bay when the vehicle is sitting after driving.

It runs very lean on second start after sitting for a while when the iat's go up. It runs very lean and idles very poorly or stalls for about 5 min of driving until the ait's come down.

I am looking at the MAT Air density table. It says it follows the ideal gas law. I am wondering if I should adjust this to compensate for my issue. Or is this something that I should leave alone. If I should adjust this what is the best way to do so?

[2swe]

well, if the ideal gas law based MAT correction was working good, there would be no MAT air density table.. in other words, you can adjust this table.

set 100% MAT correction for your actual ambient temperature (IAT), for every 6°C lower temperature add 1%, use the same slope for higher temps +6°C / -1%MAT correction
give it a try, adjust if needed.

[kaeman]

what ait sensor do you have, you need the open element sensor, if its taking 5 minutes to change air temp readings (you are probably using the closed element- Coolant temp unit), the open element unit, if its in the airflow will respond within a few seconds, I was having bad response times because my sensor was in a dead air spot so the manifold would heat soak the sensor also. If you are not using the coolant sensor then try the sensor out of the intake air and check the sensor response close hood see how long it takes for the sensor to read the temp under hood, then open the hood take the sensor our of the engine compartment and see how long it takes to go to the ambient temp. have a small fan or something blowing on the sensor. All this is easy to check by data logging the sensor and checking the time. You might have a sensor that has a very slow response and needs to be changed out.
Good Luck

[Dennis930]

maych87,

911 air cooled engines are very good contributors to heat soak because of the fins on the cylinders and the hot exhaust directly below radiating heat upward to heat everything in the engine compartment. As kaeman said, if you are not using an open element IAT sensor, you need to switch it out. It should not take 5 minutes for it to settle out.

Do you know what your CLT is reading when hot starting? What sensor and where is it located? For my installation, CLT can be 220* - 275* in the summer. To combat heat issues when restarting the engine I use ASE to add a little fuel at these higher temperatures. My intercooler actually heats the air for awhile until enough air flow cools it off. I changed ASE taper from engine cycles to 0.1sec units. Note that ASE taper graph units will still be labeled "taper cycles" after changing the units. For mine, I started increasing ASE taper time @120* and increased it as the temperature rises until @220* and above I have 95sec of ASE(I started off at 2min but have since backed it off). My ASE% is 4% @220*, but this can be tuned for specific applications. So, this is something you can try if you like.

[maych87]

Thanks for the responses. I do have an open element sensor. I’ve been messing around with the settings. I have it abit better. I will try dennis930 sugestions


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