How post-cylinder EGT relates to pre-turbo EGT

[Mk3ukr]

Hello all
Great forum, I read and learn a lot rom here since I purchased my Aquamist 1s system 4 years ago. My question is not exactly WI related, but I hope to get comments from knowledgable guys.
Recently we had discusiion about correct placement of EGT sensor. Some people install it in one of the cylinders runners, I always installed mine pre-turbo. My opinion is pre turbo EGT is higher than post-cylinder, I don't know for how much, possibly 50-70C higher. I think it depends on how big restriction gas side housing represents. My collegue who drives heavily modified WRX argued he never saw more than 800C from stock pre-turbo EGT sensor and regularly see close to 900C on his Greddy gauge (sensor tapped into the one of the runners
I work as marine engineer and know from experience that it is very common to see on diesel engines cylinder temperatures let's say 430C (we have thermometers on every cylinder), pre-turbo ~510-520C, post-turbo ~430C. I know when hot gases collide entering the turbo their teperature goes up.
I believe the same laws of physics can be applied to automotive turbochargers. Or am I missing something?
Thanks

[JohnA]

Originally Posted by Mk3ukr

... My opinion is pre turbo EGT is higher than post-cylinder, I don't know for how much, possibly 50-70C higher....

If the turbo is only creating a 50-70C temp drop at full load, then it's not matched properly to the engine.
100C+ is more like the target for an efficient system. :smile:

[Mk3ukr]

I meant temperature Increase from post cylinder to pre turbo.
I never seen this subject discussed or described anywhere
Thanks

[Gert_]

Received this from a tuner recently, when I told him my EGT went up to 930?C, probe is post cilinder:

Gert,

If the engine is going to run continuously at WOT like in a race boat, then 930 degrees is the safe maximum if the engine has inconal valves. As your car is a road car that touches these temp for brief periods they are ok. It is common for a drag race engine to record over 1000 degrees.

Under the turbo is much hotter when you run rich mixtures, as the unburnt fuel burns outside the engine, in the turbo collector. Most people do not know this and they will often say "It makes no sense...I make the engine richer and the exhaust temp goes up". Any time I hear this I know exactly where they have put the probe.

The problem with people with EGT on their engines is, they are constantly watching the gauge and worrying, instead of enjoying driving their car. Most of the worry come from all the misinformation on the Internet.

[Mk3ukr]

It is interesting info, looks like I have to stop worrying about my EGT touching 900C ocassionally. Will set my Greddy gauge warning to 920C tomorrow :lol:
I wonder how reach is reach mixture which keeps burning in the exhaust. I try to stay at 12.0-12.3 AFR level at WOT. Not too reach I hope
Thanks

[hotrod]

Highest EGT's are supposed to occur about 6 inches (20 cm) past the exhaust valve. As mentioned above this is partially due to the rich fuel mixuture continuing to burn as it exits the exhaust valve and the transition from the watercooled cylinder head into headers that have have very limited cooling. The rise in exhaust temp with richer mixtures also depends on where you are on the AFR curve. If you are running lean richening the mixture will cool down EGT's if you are rich of max power adding fuel can increase EGT's.

Part of the answer is why are you using the EGT gauge. In aircraft they put it infront of the turbo and watch the Turbo Inlet Temp (TIT), They also have Cylinder head temp sensors on the air cooled aircraft engines.

On autos most folks put it a few inches down the exhaust runner and are watching max Exhaust gas temps.

On the WRX max rated turbo inlet temp is 1625 degrees F according to the turbo manufacture (mitsubishi), most folks get nervous when EGT's taken in the exhaust header just outside the port read over 1600 deg F.

Larry