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Norm K's Avatar
 
Join Date: Sep 2012
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Cylinder Head Temp Sensor

About to embark on my EFI conversion and have what might seem like a silly question. Iíve compiled nearly everything I need to complete the conversion but have yet to pick up a cylinder head temp sensor. Iím not looking to scrimp but I am an unabashed fan of alternate solutions, particularly when thereís money to be saved. I suspect there are a myriad of reasons why the answer is no but given the potential savings and the simplicity of installation I figure itís worth asking.

Finally, then, my question: If the 914 CHT sensor has the same thread diameter and pitch as the air-injection plug holes (from what I read theyíre the same) on a 930, could the CHT effectively be taken there?
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Old 01-23-2014, 10:47 AM
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It may be just my experience but I have tried a myriad of locations for "coolant" temperature sensors and found the CHT to be the least helpful in warmup settings. My coolant sensor is currently in the breather cover after trying cylinder the head location (I have 3.2L heads which have provision for CHT sensor) and both chain boxes.
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Old 01-23-2014, 12:06 PM
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Will the 914 CHT take EGTs, much less a 930's EGTs? Doubtful.
Do exhaust gas temperatures reflect the engine's warm-up cycle? No.

Results can vary, and ours are different to sjf911's results.
We find CHT most helpful, the strongest correlation to actual engine temperatures, and suspect that's why all the EFI air-cooled 911s and Turbos used head temperature.

With ~8 quarts of oil in play with the thermostat shut, it takes a long time for the oil to reach operating temperature. That's not useful.

You don't have a lot to lose by trying a sensor in the crankcase breather, like the 1994 Turbo 3.6. If it doesn't work out, pick an alternate sensor and location.
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Old 01-23-2014, 04:21 PM
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You know what baffles me? After about 140-160*s all the way up well over 300*s of CHT, you don't need to adjust fuel mixture.

You'd think the hotter the cylinder, the less fuel you need, but you don't.

It truly is for warm up (no additional fuel is required after around ~140-160*).
Old 01-23-2014, 05:39 PM
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Yup. After warm-up, the AirT at the throttle body is the critical temperature input.
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Old 01-23-2014, 05:43 PM
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Yep, super duper important. So important, I had to adjust the curve of my air temp correction as it's not linear. Apparently has to do with the Ideal Gas Law.

Fully tuned in warm weather produced pig rich in cooler temps. Had to adjust air temp curve down about 5% from 100 down to 60 degrees.
Old 01-23-2014, 06:26 PM
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