EGT Theory as it might Apply to Rotax Max

I started karting in 1966. Soon after I started in I KF there was an article in the Karter News about the advantages of using an EGT. It was written by the people at Bystrom Instruments. It put a bug in my ear that never went away.

In 1985 I built a water break dyno. In addition to the built-in tachometer and strain gauge, I attached an EGT, a CHT and another tachometer. I have been a firm believer in the benefits of the EGT ever sense. With an EGT the CHT is relegated to a minor function, almost superfluous.

There are a couple of things that need to be learned when using the EGT. First, the EGT is very very fast to register on the gauge. 2nd, when you get detonation the EGT will read lower.

This can cause some confusion in that you may start getting some detonation before you reach maximum EGT readings. A KT100, under normal circumstances, without detonation, will end up with an EGT reading of 1100 to 1200° at peak RPM. Less than that can because by 2 things, too rich or too lean. Unless you can hear the engine detonating (too lean) it’s hard to tell why it’s reading lower than maximum. My advice is always go richer first. If the EGT reading goes down, do the reverse and see if it goes up. Continue that process until you get the desired reading. Do the same thing on the low end with the low-speed needle. There’s some skill involved, but you most likely will soon develop that skill.

I was at a Sprint race in California when I first encountered someone with a EGT. He had just stuck his motor. I heard him explaining that it was only reading something like 800°. “I kept leaning it down an it kept going down!” he said. He obviously should have been enriching the mixture. Don’t make that mistake. Always enriching before leaning! The CHT can sometimes be an indicator of too rich or too lean. If the CHT is going up and the EGT is going down, too lean. If the CHT is going down and the EGT is going down, too rich. Just remember, the EGT is very very quick to register the exhaust gas temperature.

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