Forget the relatively useless EGT gauge and get yourself a built-in wideband O2. I have a GReddy EGT gauge (with the probe in the collector centered directly under the turbine entrance) and also a $1750 Heraeus EGT monitoring system with a probe on each header runner. The Heraeus system is practically instant-reacting and makes the GReddy type gauges look silly in terms of quick and accurate temperature measurement. But even the Heraeus system with its quick reaction time is almost useless for careful tuning.
What you NEED to know is the AFR. I have an FJO wideband and I can tell you from extensive experience that you CAN NOT spot AFR variations with an EGT guage until they are extreme -- at LEAST one FULL A/F point, and that's if you can carefully control other variables such as length of the pull, fuel quality, etc. Also, you CAN NOT identify lean or rich spots in the RPM/boost range with an EGT gauge -- you can only get some vague idea of where the EGTs peaked over the course of the pull. And, what little info you can gather through EGT readings can only be done AFTER you have correlated the EGT readings that you get on YOUR car with AFR readings from a wideband O2. At the same AFR, EGT readings can and do vary from Supra to Supra by more than 100 C depending upon what type gauge you have, how and where the probe is positioned, the length of the pull, etc.
Here's one example (I have many, but here's a simple one): Recently on the dyno my car was encountering a lean spot in the 5500 RPM range. It would spike up into the 14+:1 range, with low-11:1 AFRs on either side of the spike. With a good bit of boost and an extended pull, 14+:1 might be enough to damage an engine, agreed? Okay. The EGT on the GReddy gauge peaked at 820 C on those pulls because the lean condition wasn't of long enough duration to give the gauge time to react. If one were going simply on the goofy 900 C Max EGT rule, we'd have thought that everything was just peachy. We tuned the spike out and got the AFR down to 11.5-12.0:1 across the high boost RPM range, and as a result EGTs in the collector went UP to 840 C. That's because the overall AFR was leaner, though the 5500 range was richer.
It is really unfortunate that so many people think they can get useful tuning information with EGT gauges. I just wonder how many engines have been blown due to this? No matter, people need to stop propagating the myth that EGTs are inherently useful for accurate fuel tuning.
Steve
I've personally seen A/F shoot to 14:1 and the EGT budge less than 10 degrees C. If we didn't have a WB we wouldn't have known to stop immediately. Makes me wonder if the EGT would save you in time. Good thing our engine can take some abuse.
