Max EGT? Options

[technicalninja]

The title is the question.

I know what to look for with water-cooled stuff.

I have no experience with air-cooled stuff yet...

What say you?

Is there a normal range?

A never exceed number?

Anyone ever use 4 thermocouples?

Was there any noticeable difference (#3 is of concern to me)?


Thoughts, tips, any data would be greatly appreciated!

[GregAmy]

What's your goal with installing EGTs?

I'm a pilot (as many on board here are) and the point of EGT in an air-cooled airplane (almost all of them are) is to properly set the mixture, as easily as possible. In your typical General Aviation airplane, the pilot controls the mixture.

You don't have that problem in the 914, so why bother with EGTs? If you're looking for tuning, you're better off using established guidelines like AFR and CHT, of which we have a lot of experience, on the dyno.

And you're incorrect that it's "fixed throttle" and/or just "cruise numbers"; it's managed by the pilot in all phases of flight, regardless of whether it's fixed-pitch or constant-speed prop. Generally speaking, I would agressively lean on the ground while taxiing to keep the plugs clean (of lead deposits, mostly), then go full rich on departure to minimize the EGTs and CHTs. As I pitched down for cruise climb I'd slowly reduce the mixture until I got a light roughness then give it a wrist-twist rich (vernier mixture). Once I got at cruising altitude and RPM started to rise (fixed-pitch prop) I'd richen then lean to a slight roughness, note the EGT, and give it about 75-100 degrees richer. On descent under lighter load I'd pull the mixture back leaner to keep the plugs clean (and reduce fuel consumption).

Very few GA airplanes came with EGTs, they were commonly add-ons. So we learned to fly by the seat of the pants. But this overall technique (along with massives on the bottom spark plugs and fine wires on top) resulted in clean plugs and cylinders that lasted for a thousand hours or so (a feat within itself).

But you're doing none of that. Your mixture is fixed by either the "computer" or the jets. You cannot control the mixture in the cockpit so that knowlege of EGT is not particular useful.

If you're still curious, my recommendation is to get some dyno time and tune the engine based on the well-estabilshed knowns of CHT and AFR through the various phases, and observe what EGTs that results in. Then you'll have the info you're looking for. - GA