Quote:
Originally Posted by RETed
Brandon?
"Mean Best Torque" is easy enough to figure out - i.e. dyno.
How you figure "peak pressure'?
I assume you're talking about BMEP...
This kinda merasuring / monitoring is above what most of us can attain.
We're talking big range pressure transducers plumbed into the engine - do you really wanna drill holes into your engine???
I don't see how my page is "incorrect or misleading"?
What I wrote general supports what you just said?
-Ted
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Ted, I think I can help.
Peak torque is found where the peak chamber pressure is attained at ~12 degrees ATDC. This is a function of fueling and ignition timing at a specific engine speed.
Most EGT writeups mention peak torque (ignition timing wise) as being the low point in the EGT map. This is primarily true (with a few far-reaching exceptions).
As you said, peak torque timing is obtainable on a dyno. However, most people who tune using EGT are doing so because they are not tuning on a dyno. Also, many people do not have enough nerve to advance the timing until power starts falling off so they don't know if they actually found the peak of the curve.
As to your writeup, I think this is what he takes exception to:
Quote:
Going leaner than best power will raise EGT - the dyno should also
show the engine LOSING POWER. This is due to inaudible detonation. If we go
leaner, EGT will start to skyrocket and detonation is pretty evident. From best
power, if with richen it up, the EGT will actually go DOWN for slightly richer
conditions. You still get almost complete combustion, but the extra fuel cools
everything down. If we richen it up substantially, it'll come to a point where
all the extra fuel will start to ignite out the exhaust port, and this will cause
the EGT to rise (this looks exactly like lean!) and sound like detonation, because
the excess fuel is igniting in the exhaust system; this is when too rich will also
raise EGT.
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If you research this carefully, you will find that the higher EGTs from lean combustion is due to the slower burn rate of a lean charge (later burn = lower expansion ratio). You should NEVER see this condition with a turbocharged car on the dyno. In fact, the chances of the ignition system being able to light a high-pressure lean charge are not very high. You will see it if you run a lean cruise in vacuum (lean of 15:1).
With a turbocharger, the time when the EGTs start to rise is the point where all the fuel is being burned. This will be significantly rich of peak power. The unburnt fuel cools the combustion charge as it absorbs some of the combustion heat to vaporize. Very few people tune turbocharged engines to run lean enough to make peak power on the dyno (13.0-13.5:1).
I have not found any information on the rich side (rich misfiring) in any books. Your explanation makes good sense (as long as there is additional oxygen in the exhaust that allows combustion to occur).
I think your write-up is very good, it explains the variability of the sensors very well, gives good base ranges, discribes sensor behavior accurately and contains no mis-information that would cause someone to destroy an engine.
There are several awesome books that address EGT ranges and behaviors on engines. Most of what I put above comes from the Bosch automotive handbook, but I read almost identical information in "Automotive engines and Air pollution".
Your numbers and ranges are correct, but the explanations for the observed behavior are confusing and possible mis-informed.
I am probably a little to strict about data accuracy, as the write-up would not cause harm as it is.
Many thanks for providing the resources.
EGT temperature ranges??
Linear Mode
