So, don't keep us in the dark! If your EGTs go up, what should you do? How hot is too hot?

Here is the crazy part. With an AFC changing the MAF signal, if you lean the mixture out, you will also get a timing advance increase. So as you lean out the mixture, you will generally start to see EGTs go down due to the increase in timing advance! This does not mean that peak cylinder temps are lower! Quite the opposite. Increased timing advance and leaner mixtures will generally lead to increased peak cylinder temps. But since the timing advance is increased, the exhaust has more time to cool before it gets pushed out the exhaust valve and touches your EGT probe.

The decreased EGTs that you get from leaning out an AFC (and indirectly increasing timing advance) might make you feel pretty damn confident about what you are doing until the engine starts to knock, timing gets retarded, and you see the EGTs start to spike again.

This is why I am saying that EGTs are difficult to use. EGTs do not tell you what the peak cylinder temperature is. And that is what you really want to know. EGTs only tell you what the temperature of the exhaust is, and a lot of factors affect that.

Add in the fact that EGT probes have been known to break off and destroy turbines in the process, and it just isn't worth it to run one. It is hard to use an EGT to actually make a good tuning decision, and it could destroy your turbo. Not worth it.

I ran an EGT probe for years, and I can honestly say that I got very little out of it. I'm just glad I removed it before it had the chance to break.

But hey, today's EGT gauges sure do look nice for the ricer in all of us.

 

What you should do is specific to the engine types and the logged data that you have - which is, hopefully but unlikely, complete.

In Trinababe's case given the limited data, and the characteristics of the stock ECU under partial control by AFC, EGTs ARE hard to use. I was addressing the statement you originally made - potentially generally applied.

I agree that the tuner needs to know what he is doing, as well as have as complete a sensor array as possible. EGT, AFR, CHT, Ign timing, pressure transducers, all useful.

Properly designed, built, installed, an EGT probe won't be a problem. Similarly, if I said "turbocharged engines are unreliable because their pressured tract hose clamps have been known to slip off" it wouldn't be the most accurate of statements.

I respect your experience with the EGT probe and your advice specific to Trinababe's situation, but I believe that EGT is still very useful in other applications beyond what us enthusiast may get into - situations where there is a very good level of control and a wide range of data, all of which add up to give a complete picture of what an engine is doing.

Bling !



Cheers

 

Totally agree with the above.

 

Well I would like to revive this from the dead... I now have a few crappy logs of my timing. My logger refreshes VERY slowly but it was enough to see timing in a few points...Not accurate enough to tell if the ECU is pulling timing making it those figures however.

This is what I now I have to deal with: The timing from the very few points that I can see are looking really good. Seems to be around 10-12 at 4k and up to around 19 at 6,500-7k. Seems fine timing for the boost and everything else I am running. I did a bunch of pulls logging the Zeitronix again and the AFR I am now at is around 11.2:1. The thing i am wondering about is how much of a spike in the EGT's could be knock... I get a few spikes of around 30-40 degrees C. This is only for about 1/50th of a second long. Could this be knock or is it more likely just the sensor getting upset? I would THINK that if it was a spike from timing retard it would last much longer than 1/50th of a second but I dont really know at all.

Every time I have pulled/read the plugs there is no sign of detonation but I dont really want to rely on plug reading for my conclusions. I will be getting something that will read knock (Either the AEM, DSM Link, ECU Plus, or Utec) shortly but I would still like to know more about this whole conundrum.. Pretty much I just want to make myself more knowledgeable, especially considering nothing can truly deduce what is or is not knock perfectly. The more I know the better I will be. Thanks guys for all your help!

 

And if it matters... the car pulls very hard and has no hesitations or hiccups or anything that feels like it has any loss of power at any point through the RPM range. I dont know how much knock it would take the ECU to pull enough timing to actually make a difference that you could feel though either.

 

You can figure out what is knock. You just need a differnt logger with a better sampling rate. When you log timing, you look for flat spots and pulled timing. The ECU holds or pulls timing to control knock. It's not a direct knock count like 1g's can do, it just needs some interpreting.
As far as EGT's (http://www.roadraceengineering.com/newafc.htm);

If you are running too lean for the boost and octane you have in the tank, you will get knock or pre-ignition. The knock sensor bolted to the engine block will pick up this "pinging" sound long before you can hear it inside the car. When under higher boost, there is almost always small amounts of knock. At these small amounts of knock the ECU will continue to advance timing normally. At mid knock levels the ECU will hold timing and if it gets too high or rises quickly, the ECU will begin to retard timing if not pull it all the way back to zero. You can hear the exhaust note change when the timing goes away. It will turn deeper , almost rumbly sounding. When the timing is retarded, the ignition process happens so late that the flame front shoots out the exhaust port when the exhaust valve opens and blows still expanding, really hot gas directly onto the EGT probe. So internally the pistons are barely warm, but the exhaust manifold and turbo get real hot. This is the reason we recommend not running EGTs higher than 900 degrees C. That is the point that timing retard is usually driving the EGTs up. Not that immediate damage is being done, it is just that you are no longer making additional power above that temperature and there is no benefit to running there.


If you combine; RPM's, timing, O2's, and EGT's, you can do a very good street tune.

 

Well, I already knew all that Is what I was looking for is to see what a knock spike would look like on an EGT graph. If timing gets pulled far enough obviously the EGT's would go extremely high for a period of time (Not for 1/50th of a second). I was wondering if these "spikes" that i see are any sign of knock or just nothing to worry about. I will be getting something to read the true knock sum shortly and will not waste $100 on a logger that refreshers quicker.

To put it very simply in one statement, will you be able to detect knock by seeing tiny 1/50th sec. spikes in an EGT going from say 780 to 820 degrees C? Like i said before, I will be getting something to detect true knock sum very soon but figured this would be good info to know.