Joey,
What AFR and Why would egts skyrocket??
I think your understanding of Exhaust Temperature are a bit off.
AFR has very little if any effect on EGT.
It is directly and indirectly related to cylinder pressure and ignition timing.
So explain to me please why you made this comment and we can converse at length.

 

I am assuming he will be using a SAFC. If you going to be running at 11.8-12.0 your timing will most likely be higher due to being at different load points on the timing tables. Thus running higher timing. Unless he is getting his ECU custom tuned. I've always been told and have witnessed leaner AFR makes EGT higher.

 

Oh he also talking about 5th gear AFR... Thats what I understood from his first post. So 5th gear at 3000-5000 RPM at 11.8-12.0 = high timing table on the ECU due to the altered MAF signal to indicate a lower load...

 

Joey,
Advanced, High or increased timing lead will give you LOWER Egts.
Retarded, Low or decreased timing lead will give you HIGHER Egts.

Again the words high and low will be from the optimal timing value the engine needs at that particular load and rpm value.

Under many normal conditions exhaust gas tempertaure is just being "shifted" in the cycle.
Meaning that in theory there is an ideal timing value. In other words optimal for the engines current state. Lets say for example that numerical figure is 15 degrees BTDC at 4000 rpm under xxx specific load. That would be a figure that we we will say is about 10% off MBT.
For our above example we will give the engine 20 degrees of timing BTDC. That will shift Peak cylinder pressure (EGT) 15 + 5 degrees before TDC. Measured EGTS will be lower. No fuel addition or subtraction from the equation. Now retard 5 degrees from the 15 and EGTS will increase. The temperature and relative pressure is just NOT being absorbed by the moving and static components of or in the combustion process. So all the energy the engine should use for work is being wasted out to the exhaust manifold....

Just a brief example is all. Hope that helps. It is a really basic lamens explanation. Simple terms and words to express the thought. I could get into specifics but I am still here in Arizona tuning and very tired!!

Nick
Precision Dyno

 

ok cool thanks for the info But do you think 11.8 or 12.0 on 93 pump on 5th gear is safe?

 

Wait a minute...are you saying that leaner AFR will not increase cylinder temps and not have an affect on EGT??

 

I am in hot weather every day of the year around 75-99 the number that i want to reach are between 11.1-11.5 because in high rpm i was reaching 10.1 or less. I will reflash my ecu to reach that.

 

Wow, I am not going to get into a vendor debate, however as you may have a point with regards to timing, leaning of the fuel definately affects EGT's in ways not limited to ignition timing.

 

I guess this is the post I should have quoted. It seems a bit contradictory to conventional knowledge...even in the light of the valid points about timing's relationship with EGT

 

Hmm... if this is true then why does the Audi APB engine (2.7t) use EGT probes in each exhaust manifold, and why does the computer increase fuel supply if the EGT reading gets too high?

It was always my understanding that making the fuel mixture richer will lower combustion temperature due to the thermal mass of the unburned fuel.