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Jab CHT's


Whack777
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Not sure if this should go here or in the Engines

 

With all the discussion about correct jetting and keeping the revs up to reduce the heat stress on the exhaust valves with Jabiru motors, why are EGT gauges not a recommended option or even a standard engine instrument (included in even the lower cost instrument panel options)? They are not that expensive when compared to the consequence of running lean.

 

Are they not the lean run indicator I thought they were?

 

I,m LSA so I am not sure if I can retro fit an EGT gauge anyway.

 

Alan

 

 

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These gauges are not that simple for the purposes we are trying to use them.

 

The last few issues of the Jabiru tuning SBs are quite clear that the primary instrument to confirm carb jetting is the lambda meter These are not cheap especially the required "wideband" type capable of showing absolute air / fuel ratio. They are also not suitable for leaded fuels so you cannot leave one installed.

 

Proper EGT probes for 2200 / 3300 are listed around $100 ea. and the gauge I use is an amplified TSO'd one so as to give meaningful readings and be capable of running via a selector switch without resistance errors. I used four CHT thermocouples and have left them in place but normally only monitor #4 usually 20-30 F hottest. I only use the 1 EGT probe in the tailpipe because its too large to properly fit the headers, I use it as a relative guide and confirm that nothing has changed from original calibration.

 

I treat it like the recommended CHT installation: once the worst cylinder has been determined by audit or other means (wish we could still buy "colourtune" sparkplugs) it is sufficient permanently monitor with the 1 probe. Of course if something occurs such as an intake leak that condition might not be monitored, I have had this occur on an 0-200 and got plenty of clues from a rough idle and whiter plugs but nothing shown on any gauges, mag drop or cruise etc.

 

There is a case for wiring the engine up like a cardiac ward but where will this end - there is only so much you can do for a simple system before it becomes something else, its actually more reliable to ensure the jetting is suitably rich to allow for mixture scatter between cylinders, which JSB-18 seems to acomplish.

 

Ralph - 210 hrs and counting

 

 

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(wish we could still buy "colourtune" sparkplugs) Ralph - 210 hrs and counting

Is this the plug with a 'Glass' top that alows you to observe the combustion colour? i.e. Gunsons Colourtune. These are still available....ED

 

 

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Word of caution and something to think about.

 

Rich of peek EGT is cooler.

 

Lean of Peak is cooler.

 

Which cylinder is where????

 

Without an engine like an IO540, GAMI injectors, EGT sensors on each cylinder and an appropriate display, and a method of adjusting the mixture in flight.....you are barking up the wrong tree.

 

For simple engines its best to run rich of peek on all cylinders and by a fair margin because when running just rich of peak EGT you are actually in the biggest danger zone of all.

 

J

 

 

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