I was wondering how many of you guys use an Exhaust Gas Temperature (EGT) gauge. I am currently selecting gauges for my mods and have bought some nice Delphi 52mm boost and analog air/fuel gauges. They also do a nice EGT gauge also with a 1/8" NPT mounted thermocouple.

How useful would and EGT be in conjunction with an air/fuel gauge to tune the car on the fly?? I know that lean mixtures produce hotter EGT temps but is there a common rule for the absolute values to expect / aim for?? Also, looking for how to use such a gauge to help diagnose part throtte running issues like stumbles etc. Wondered if they were 'dynamic' or fast acting enough.

Also, where would the thermocouple be mounted?. I am thinking just after where the maniold merges into one pipe close to the wastegate tie in on the crossover pipe. This is the the first part of the system where all 4 exhaust paths merge. I remember I saw somwhere a pipe clamp style strap that clamped around the exahust pipe and had a 1/8" NPT boss mounted on it. I think it might have been for intercooler thermocouples. One of these would make the job easier as you could just punch a hole in the crossover and put the clamp around to mount the thermocouple.
THanks

 

I run an EGT. I'd never run another modified 951 without it (that and a wide band 02).

Also, you need to mount the probe 1" from the exhaust port. Anywhere else, and you will not be receiving an accurate reading.

 

Tony -

How about some examples of what you see for temps. Since you have both the WB02 and EGT, what you you see at certain A/F values? Info is much appreciated.

 

Sustained WOT is about 1550F @ 12:1 a/f

These are approximate values since everythings fluxuates so fast....

 

I'm with you. I have thought about doing this many times and never acted and now the damage is done. This time will be different, after this rebuild both will be installed.

From which exhaust port are you speaking? Ideal would be 4 probes and a instrument showing four readings, one for each cylinder.

 

Bump..

Looking for advice on how / where to mount thermocouple

 

lejams

I have the sensor installed in the #4 runner.

 

B951S

1" off the exhaust port.

 

The only thing that concerns me about this location, or be it near any of the singular 4 exhaust ports, is it will only be accurate based on the one particular cylinder. What happens if the probe is on #4 and #1 is running hot?

I understand that if it is located further down where the 4 exhaust pipes interconnect, temperatures will be reduced and some accuracy will be lost, however it would provide more data/indications for over-all combustion temps. What do you think?

 

lejams

The reason I use #4 is that this is the cylinder that is typically running hotter than the others.

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The farther down the pipe from the port, the colder the temp will be until you reach past the collector.

I'm certainly no expert here, but according to John Milledge, the exhaust temps can actually get hotter in the cross over depending on where you take the temps. This, again according to John Milledge, is is because of unburnt fuel that is actually burning.

I have no way to verify this one way or the other.

And in light of this, and the manufactures instructions, and per John Milledges recommendations, I mounted exactly 1" off the exhaust port.

At this location (1" off...) the temp is supposed to be perfectly accurate.

..

The solution for you, or for anybody wanting to measure more than one cylinder, is to simply use 4 gauges each with their own senders, or a gauge that reads more than one sender.
..

I recently burned an exhaust vavle. I was too busy smoking some new Lambos, 996TT's and 993TT's and didn't notice that my EGT was "pegged", and guess which exhaust vavle burned?

My EGT's, my water temps, my oil temps, etc... were all very high. Why? Who knows... but it was 108F ambient air temp. I was running 100 unleaded which reflecting back, probably was the cause.


But if you are only have one gauge, that monitors one sensor, then do the #4 cylinder.

 

TonyG,

I am certainly not an expert by any means, in fact I'm on a learning curve with this being my first rebuild.

I think this is one of those areas where a new gauge/device is needed, something that would account for each cylinder, i.e. one gauge with 4 rolling temp. reads, collecting data from 4 separate probes. If one were available I'd buy one today.

I was'nt racing so my damages probably occurred over some period of time.

As you stated #4 has always been the culprit - I've experienced vaporized plugs on #4. #4 has always been my greatest concern, but not the one that bit me.

Recently I burnt a valve on #4, but when the head was removed, a nasty surprise on #1 - detonation on the head of the piston and severe scoring on the cylinder wall. The one and only conclusion is this cylinder was hot and I never had the first inclination.

Based on this experience my concern is that if you are only monitoring one exhaust port, we are really only getting 25% of the crucial data.

I hear what your saying about John Milledges conclusion, but I wonder if it's possible to calculate an average temp. for all 4 cylinders compensating with some degree of reason for temperature variations due to other factors as You/Milledge stated?

I think that this type of data is critical and would save allot of engines if it were available and used.

 

lejams. If you want 4 egt probes and one gauge,you can get one at any avionics store,such as http://www.aircraftspruce.com/index.php. They even have them with alarms that you can set,so you never have to worry about forgetting to check your temps.

 

MySwiss,

Thanks, I will look into it.

 

Agreed on all the points...

You can get EGT gauges that will monitor more than one probe.

You cannot, use more than one probe, with some switching device, to control one gauge as the resistance of the wiring is exact and calibrated to the gauge.

My personal feelings, and is why I did what I did..., is to only monitor the #4 cylinder as it's the one that's running the hottest.

If you calibrate to the hottest cylinder, the the other 3 will be safe by default.

Plus... and don't laugh... I wanted all my gauges to match! :-)

 

Also, you could have had the piece of the burnt valve bounce around and ding the piston top and combustion chamber. It's pretty common, and is more cosmetic damage than anything else. Also, this "dinging" can look like detonation marks...