Quote:
Originally Posted by brucepick
theunchosen, I follow your reasoning but there's a piece that I want to question.
First I have to say I don't have the background I should as far as typical temps for combustion, exhaust and cat operation. I tried doing some quick research but I'm not finding the data easily.
Anyway, normal stoich EGT at part throttle will be x but in lean burn it will be 1.5 x or 2 x, I suppose? This hotter lean burn exhaust is likely not hotter than normal stoich cat operation??
If so, the hotter lean burn exhaust wouldn't damage the cat or oxy sensors BUT -
As you wrote it probably heats up the head more than usual. Would watching the ECT display on ScanGauge reflect this? - or would the high temps be local to the cylinder walls and not be reflected in the ECT data from the ECU?
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The temps in the cylinder will be greater and the exhaust temps will be greater, but they are going to dissipate heat fairly quickly in the exhaust pipe. Even over just a few inches heat exchange between 1660 Rankine and 500-600 rankine have the potential to be rather large. That said your cat usually runs as hot as the exhaust gas because its burning excess fuel. if the exhaust gases are the only thing thats reaching the cat and heating it they are going to be cooler than they were when they left. Your o2 sensor should be just above the cat so it should reflect the temps as they enter the cat. I would gamble the emissions software in the ECU mandates that the cat stays around 1100-1200 degrees F. I would expect that the gases could cool below that before they reach the cat(since Lean burn is only going to engage under low load(for you that probably means low rpm and low flow)).