[Fot] EGT gauge installation

Thu Mar 7 03:01:34 MST 2019

Almost every car in our classic race championship has an AFR sensor nowadays and it should have, for power and for the safety of the engine. Even if the driver is an expert plug reader, an AFR sensor is giving more information on all the different circumstances at a racetrack : all you have to do is to look at the gauge regularly and after some time you will know what AFR ratio is safe and is giving best power. It will allow to adapt the carburettor jets and maybe the ignition timing. So far I did not see EGT probes in the cars of our championship. On my engine dyno (Stuska) I use the 4 EGT probes. The reaction of the EGT probes is almost as fast as an O2 sensor, but I think the AFR ratio (or the real time fuel consumption) is an easier and exact way to tune the mixture. I use the EGT gauges to be aware immediately when something goes wrong : when the T° readings of one of the probes goes too low or too high, an alarm goes off. In this way, it shows immediately when i.e. a plug does not fire or a valve is sticking etc. 
The EGT reading of no 4 cylinder is mostly 5% higher than the rest : I thought this is because of the distance and positioning of the probe, but of course it can be the consequence of a leaner mixture in no 4. But the distance does matter : when you have experience with an oxy/acetyleen welder, you know that the distance to the part you are working at is all important : the T° is lowering very fast with the distance. I think the same goes for the EGT probe in the exhaust flame. With 2 carburettors and 2 EGT probes, I would use cylinder no 2 and 3 because these exhaust primaries have the same shape and you get 1 probe for each carburettor. But then no 1 and 4 is a more convenient installation... 
Marcel 

Van: "fot" <fot at autox.team.net> 
Aan: fot-bounces at autox.team.net 
Verzonden: Maandag 4 maart 2019 14:47:28 
Onderwerp: Re: [Fot] EGT gauge installation 

As far as AFR gauges vs EGT they both have their place in/on a race engine. AFR will get you and average of all the cylinders at any given moment. The down side in a 4 banger is the outer cylinders #1 and #4 are always a little leaner than #2 and #3 due to the nature of the design of the engine and intake. If used correctly, and if you get the right design and quality of probes, the reading can be almost instantaneous. Use a good quality exposed tip probe and they reaction time is as fast as an tachometer which we all use to gauge RPM’s so that is pretty fast. If you buy a sealed Inconel probe the reaction is slower, but still good enough for most people. I use both on all cars as a failsafe. The EGT give me the info on the outer cylinders which are the one most commonly damaged by being too lean. The AFR tell me that overall I am OK. I buy an EGT thru Auber Instruments. You can get a 2”x2” digital that reads in red for one cylinder and green for the other. They have the quick response exposed tip Type K thermocouples and the whole deal is 160.00 or so. The best part is the digital gauge has recall of the highest reading and it also has a warning light that comes on by whatever temp you select and set it al. Helps to keep you aware of what is going on thru visual info vs watching the gauge all the time. You can even hook up a buzzer if you want. They also have single gauges for one probe, but the cost of two is higher and you got to install two for power and ground and such so why would you. One of my cars has two Auto meter EGT’s gauges, while fine and the quality is first rate I have to be the monitor to see what is happening as it happens. Sometimes at the end of a straight you can be quite busy and don’t have time to see two EGT’s gauges. If I hasn’t made up such a nice engine turned aluminum dash I would swap them out, but alas I am stuck with two 2” holes if I do. As an aside the O2 sensor of a typical AFR will read inaccurately in our cars too if you run leaded race fuel. Over time the readings will changed based on how much leaded fuel it has been exposed to.. The lead gets on/in the sensor and fouls it, so you got to replace them when that happens. For most of us that’s a long time but you got to know it anyway. 

Hope this helps you guys. 

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Mark Craig 
Diesel Performance Parts, Inc. 
411 Allied Drive, Nashville, TN 37211 
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