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 EGT Note

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edlithgow
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Registration date : 2010-06-01

PostSubject: EGT Note   Tue May 24, 2016 1:13 am

A quick look at EGT for tuning. These people will be using high temperature thermocouples, though, which I'm unlikely to bother with.

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"Retarding the ignition timing will generally raise the EGT at the same AFR. One engine might make best power at 1350 degrees while a very similar engine might be happier at 1500. You can't guess at this or you are simply wasting your money on the instrumentation. Wankel engines have higher EGTs than comparable piston engines due to their lower thermal efficiencies. 1800F is not uncommon here.

Some gauge manufacturers say you should tune to achieve maximum or peak EGT for maximum performance. This is incorrect. Peak EGT generally occurs at an AFR of around 14.7- 15.0 to 1 on gasoline. This is far too lean for maximum power and is dangerous under continuous WOT conditions. Many people think that the leaner you go, the higher the EGT gets. This is also incorrect. Peak EGT occurs at stoichiometry- about 15 to 1 for our purposes. If you go richer than 15 to 1, EGT will drop and if you go leaner than 15 to 1 EGT will ALSO drop. It is VERY important to know which side of peak EGT you are on before making adjustments. It is safe to say that peak power will occur at an EGT somewhat colder than peak EGT."

I don't need peak power or continuous WOT so peak EGT would probably do me.

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"A rich mixture will see high EGT temps because the air fuel is still burning as it gets pushed out the exhaust valve.  As the AF gets leaned out the EGT will drop, but then around 14.6 it will start to go up again and even faster till the motor gets so lean it will barely run.  Ignition timing also plays a major role in EGT temperatures.  An overly retarded timing at a safe AFR will give incredibly high EGTs, just as overly advanced timing will also do."

Directly contradicts above (which is more convincing)

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"From the peak EGT, either increasing or decreasing the fuel to air ratio causes a change in Exhaust gas temperature. Richer EGT cooling occurs because there is excess fuel cooling the exhaust stream via less than optimum burning, and leaner , heating occurs because there is excess air (oxygen) making for a hotter burn."

Directly contradicts itself (which is unconvincing)

Its surprising (though, having worked in IT, I'm no longer surprised) that so many companies think its a good idea to get illiterate ignoramuses to do their technical writing.
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EGT Note

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