howdy just got the mgl ems installed in my 601 powered by 3300. Never had a cht or egt monitoring. Surprised to see a decent spread on the cht between 280, and 320 f. Egt are are pushing 1400 on cruise....just had the carb overhauled with all new parts from bing and got the updated needle from jab. Manual says egt should be between 1200 and 1380.... am I too hot?...mechanic said 1400 is perfect . He said 1600 is too hot. Opinions please.

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I've always had mixed feelings about this topic!  Jabiru is adamant about staying within their specified EGT limits, but Mike Busch (the "Savvy Aviator" maintenance guru and AOPA contributor) has a totally different take on this issue.  "IF" I understand his analysis correctly, absolute EGT measurements are not "real" and are meaningless -  relative EGT measurements can be useful diagnostically.  The critical absolute temperatures are CHT's, which more accurately reflect the stress to which the cylinders and valves are being subjected.

Mike has written a number of articles and given a number of seminars on EGT's vs CHT's.  Just Google "Mike Busch EGT CHT" and you'll see what I mean!  He has a YouTube video seminar on this subject 1h 43min long!  But, one of the most concise summaries is here. 

The latest 3300A maintenance manual (JEM0002-7 / June 2016) lists 1364F as max cruise EGT and max cruise CHT at 356F.  In my STOL 750, my typical CHT's are 250-275F in winter and 275-300F in summer (measured with probe attached to hole between the plugs and the probe is insulated from cooling blast air, which generally gives a closer-to-true CHT vs the original probe ring under the plug).  I pretty much operate in upper 1200's/lower 1300'sF EGT's on take-off and climb and 1350-1400F in cruise, all the time keeping an eye on CHT's to ensure they are well below the published CHT limits.  I feel very comfortable operating within these parameters and so far have 580+ relatively trouble-free hours.  So, I guess I'm a little closer to a "Busch Believer" than a "Jabiru Believer" on adherence to EGT's.

One significant factor in my experience is that I switched from the Bing to an AeroInjector throttle-body carb.  This gave me a mixture control which gives me the ability to very precisely control the mixture and hence the EGT's and CHT's. 

I think your EGT's are fine if your CHT's stay within limits!

John

N750A

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