Installing an EGT gauge

An EGT gauge is a gauge measuring the Exhaust Gas Temperature. There is an optimal temperature for the combustion. In general the 'colder' the exhaust gasses are, the richer the fuel mixture, the 'warmer' the exhaust gasses are the 'leaner' the fuel mixture. Until you come to a point where there is too much oxygen for the fuel (over-lean) and the exhaust gas temperatures will drop again. So when tuning you need to know on what side of the optimum you are. Together with a good Air / Fuel gauge (lambda signal or Ox signal) you can thus fine tune your fuel management. EGT's are measured in various applications including R/C cars and lightweight airplanes.

The optimal exhaust gas temperature is about 925 degrees Celsius. This is about the hottest the exhaust gasses may get. If your gas is anything hotter, you're running too lean and you can easily damage a valve or blow a piston. The absolute red line for EGT is 950 degrees Celsius, this is when my gauge gives a warning to the boost controller to cut boost.

This temperature must be measured as close to the exhaust port of the head as possible. This gives you some things to consider: you can install the temperature sensor just there where the gasses leave the head, but then you will only catch one temperature signal. Installing four or six temperature sensors in one engine might sound a little overkill, but in fact this is the only GOOD way of measuring the exhaust gasses. The moment the exhaust gasses leave the head, they will already loose some temperature, let alone how much temperature is lost in the turbine. 

Most people are not so fortunate to be able to install six temperature sensors in the car. Moreover it's quite hard to visualize all temperatures at once, although it might be a good solution only displaying the hottest outtake port.

If you have one probe only, just like the rest of the world, you can choose the following locations to mount it:

	Location 1: The most easy location to mount the temperature probe is on the turbo elbow next to the Oxygen sensor.  This is easy because you can tap the hole while the turbo and exhaust is still on the car!! A better way would be getting the elbow off, but still, it is possible.
The bad side on this mounting location is the accuracy. First of all it takes some time before the exhaust gasses reach the probe. Well, this is not a real issue, as gasses are very fast. Second issue, is the turbine wheel will take a certain amount of heat from the exhaust gasses. How much heat is not known. So in short, this mounting location doesn't give you very good readings. It can give you an 'indication' but you would like to know the temperature from the combustion, not from the combustion minus the energy taken away in the turbo.
Location 2: As I told you before, the thing you want to measure is as close to the head as possible. Dean Marcum solved this by putting the probe in the last runner of the exhaust manifold. This is a good decision, as the last combustion chamber is generally the hottest. This is because it is the farthest away from the radiator. The bad side on this location is you cannot monitor anything what is going on in the other five cylinders.
	Location 3: The last good option I can think of is putting the probe where all runners of the exhaust manifold come together. On the 7M engine it is almost impossible to tap into this location in the exhaust manifold, but as the turbo screws onto this location you can put the probe in the turbo, just as I did (picture on the left). Having the probe here gives you accurate readings, but won't tell you which cylinder is malfunctioning of course.
If you are going to put the probe in the same location as I did (I mean, in the exhaust housing of the turbo), you should really look out where exactly you mount the probe. The probe must not interfere with all the oil lines and other objects in the car such as the dipstick. The next picture shows you where I mounted it, if your lines etc. are still stock like mine, you will not find any problems mounting everything back on the car.
	To make the whole story complete, here is where I mounted my EGT gauge. In the A pillar.

Special thanks to:
    Nick Holden for sending me the post turbo EGT picture.
    Dean Marcum for showing his EGT probe location while I was over in LA.
    Sharif (90T) for the hint that EGT goes down at very lean conditions