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arkansasfiddler
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another quick ques.; if a turbo engines fuel delivery is slightly excessive (fat) isnt it logical that increasing boost a little would tend to lean it out somewhat (increase egt) because of more air delivery, hence more power? what is/is there an optimum egt?
 

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yes, the more air you pump for a given amount of fuel, the leaner the a/f will be...

On the other hand, no matter how rich it may be, it will not prevent detonation once the threshold has been reached so one may not simply be able to add boost to obtain a given a/f...one may have to slack off the boost, and remove gas.

Every car is different, and the highest egt without detonation may not always be the most power making...only experimentation will find that point.

Most seem to run between 1500-1600 degs from what I have seen.

Obviously, these temps may be affected by type of egt probe, speed of response, probe location, type of fuel, cylinder head material, coolant temp, ambient air temp, alky injection, and yada, yada, yada :)

Also remember that one can suffer rich detonation as well as lean so one has to have a basic understanding as to what is going on. A wb o2 can help in this case...and experience is of help, too.
 

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EGT can be misleading, too, in that detonation actually lowers EGT. So, it's nice to have a knock gauge of some kind, no matter what else you are using to tune. Otherwise, you might have some carbon build-up, or some bad gas, or something, causing detonation, when you didn't have it before. The EGT would do down, and you might be fooled into doing the wrong thing, as far as changing A/F ratio.
 

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arkansasfiddler said:
another quick ques.; if a turbo engines fuel delivery is slightly excessive (fat) isnt it logical that increasing boost a little would tend to lean it out somewhat (increase egt) because of more air delivery, hence more power? what is/is there an optimum egt?
Raising the boost doesn't mean you're going to push any more air through the engine. Most boost means you're also raising the air temp leaving the compressor. So while you might have more boost pressure, the air is getting less dense, and their comes a point where any given combo just ain't going to flow any more air.

Increasing the air temp pf what's leaving the compressor housing, raises the EGT. The hotter in, the hotter out.

EGT peaks at Stoich.. Lean or Rich of Stoich. and the temps drop. EGT is about how close to the thermal limits of the engine you are. ~1,800dF is the max you want to see. For an engine to live with EGTs of 2,000dF means some exotic inner workings.
 

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EGT peaks at Stoich
Bruce, are you sure about that? I know that the flame temp in the combustion chamber peaks at stoich. But I was wondering if faster or slower combustion might have an effect on EGT. I know that running the timing retarded can lead to burning in the exhaust ports, and glowing hot headers. Maybe running too rich or too lean might have some similar effect, again, depending on where the probe is.
 
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