[al lkosmal]

Both sensor locations are a trade off., but the ECUs provide you with the ability to taper off the enrichments, based on the temp from either approach....I remember having this conversation a while back....

Ingo provided this input, which sums it up best.

"In an air-cooled engine the cylinder head temperature (CHT) raises much faster than the temperature of the entire engine block. Megasquirt uses the temperature reading to calculate the enrichment during warm-up. A CHT sensor is not the best solution here to tell what is going on in the engine, especially if you use the washer-style thernocouples at the spark plugs. The 964 and later engines use a sensor mounted into the heads away from the plugs.

In general Megasquirt uses the engine temperature to calculate the warm-up enrichment. You can either use an oil temperature sensor or a cylinder head temperature sensor. In both cases Megasquirt allows you to calibrate the sensor response.

Fact is that the oil temperature goes up rather slow while the cylinder head temperature goes up much quicker during warm-up. Once you decide which way to go take readings of the "cold" engine and the temperature once the engine is all warmed up. Since Megasquirt allows you to modify the calibration curve that translates the temperature into an enrichment factor you can compensate for the sensor characteristics. In other words, if you use the CHT make it richen up the mixture until it is almost at operating temps. If you use the oil temperature, dial back enrichment as soon as you see the oil temperature raise across 140 degrees."