Contour Enthusiasts Group Archives Forums Modifications Forced Induction EGT/Pyrometer gauge, worth while or not?

I'm disagreeing with you on an academic level.

It will read the temp of the exhaust minus however much it cooled between the head and the probe. Wherever the probe is at, this is what it reads. This is always the case since the exhaust temp is soooo much hotter than the metal temp, even the metal around the combustion chamber. If the metal in the combustion chamber ever approached the temp of the flame temp...it would melt. The heat just flows so quickly through the metal that it never reaches the temp of the exhaust.

So no matter where you are putting it you get the temp of the exhaust at that point.
All you do is determine how far you are from the combustion chamber and adjust your expectations of exhaust temperature accordingly.
For example, in the clamshell header of the stock exhuast manifold next to the factory O2 sensor I would run 650 C in cruise and approach 850 C under full throttle.
Mounting it in the last set of mild steel pipes I used in the y-collector it would read around 500 C cruise, 700's under full throttle.
Now with stainless piping and full header wrap, the heat is not conducted out of the exhaust that quickly so it retains its heat. I cruise at 600-650 c, Idle at 350 C or so, and full throttle around 800-850 C.
So it doesn't really matter what the temp or location is, assuming it is close to the source of combustion; relatively speaking as compared to the whole length of the exhaust. It matters more that you determine your "Calibration".
The way to do this is to test your car's air fuel with a wideband at cruise, idle, and wot and record the wot measurements at several rpm points.
Then as long as you know that your air fuel is spot on, then the temperature "has meaning" no matter where you put the probe because it will now be your reference temp at that ambient temperature. As long as you don't change the type of pipe, wrapping, or location of the probe. Otherwise you just adjust your expected temps accordingly.

The temperature never remains constant under wot, it will constantly increase as the rpms increase, so he will need to watch how it climbs and learn what is normal.
After having it for a while and knowing what the temps mean, it becomes second nature to know that combustion temps and therefore A/F is correct... just by watching that one gauge.

You can mount it further than 1" from the head, but just make sure it's reading ONLY ONE CYLINDER. I f'ed up and mounterdit in the collector so it reads all three cylinders. Hence my temp are too high, even though it's not really running hot. Think of it this way - rather than being hit by one exhaust pulse every 4 revolutions it's getting hit 3 times - so it doesn't have time to cool ever and thus reads high. Make sense?

Here isd the diagramatic representaiton of what I am trying to get across:
http://www.stevetek.com/R-EGTprobeLocation.html

OK, that shows that it ran 150* hotter when in the collector and it was more or less an average temp. Their theory is that a lean condition can be over looked and unnoticed if the sensor is tapped in the collector as it'd average out the temps from the combined runners.

Now from a novice POV, I could see having every runner tapped to be able to see which every bank temp is and having it worth while. But, to only have one out of six banks tapped in hopes of catching THAT bank running lean doesn't seem optimal.

Teamed with good upstream o2's and the wideband o2... shouldn't I be able to accuratly use an EGT for tuning if it's mounted in a header collector?

No. If you read what I am saying - I get good umbers on my A/F ratio (i.e. rich enough) yet cos I have it mounted in the collector it says it's too lean >1600�°F on WOT.

When I remount it it will be in either cylinder 1 or 4 as they are the furthest down the fuel rail from the inlet of the fuel rail, thus more prone to getting less fuel then cylinders 6 or 3, thus more prone to being leaner.

Hence you want to mount it in the header tube of 1 or 4. OK?

You could always weld in 6 bungs and close off 5 and then move the probe from cylinder to cylinder