333pg333

Thanks Wayne, that's pretty much what I came to as well. What effect does say the size of your headers have, or if they're coated / wrapped. Would going up in size of intercooler / pipes have an effect? If this is the case then what about opening up all your breathing, or is that too much in front of detonation if you know what I mean?

Duke

Excessive richness will raise the EGT. Measuring in the crossover I would say you don't have to worry if you stay below 1750.

Chris White

that’s right - richening the mixture won't help. The only thing that will help is to advance the timing (this will also get you a little more power). But to do this you will either have to run less boost or better fuel.

Bill

I use the Zetronix data logger to measure my egt. Number 4 cylinder. City driving at around 2500 rpm the egt is usually around 1250. Freeway at 2500 rpm is usually around 1450. Constant crusing at 4500 rpm on the freeway, it has crept as high as 1650. 1650 worries me.

I do not remember where....but I read an article that Porsche put out on the 944 engine that used the term "thermally optimized combustion". It was in reference to the DME strategy for fuel efficiency. I do not know all the engineering behind "thermally optimized combustion" but the higher the cumbustion temps, the more complete burn you will have, and thus the better the fuel economy. I believe this "thermally optimized combustion" is the culprit behind all the smog failures. High combustion temps also create NOX. High NOX seems to occur on all our cars.

Most articles that I have read on egt seem to recomend temps around 1200. With such high egt levels, its no wonder that Porsche used expensive sodium filled valves, ceramic lined ports and stainless steel headers.

The article also noted the "fuel shut off at closed throttle" strategy.

toddk911

Correct. The hotter the better for power and fuel economy, but not for safety. Which sets the stage for the balancing act of most power vs. NOT blowing HG.

Thanks to people like ST and Laust and others that have really pushed the boost limits we are seeing it is no longer theory that pressure does not blow HG or motors.....HEAT/KNOCK blows them. If your a/f & timing (EGT's) are spot on, you can run a LOT of boost.

toddk911

If you are measuring EGT's in the crossover you will getting flase low readings; i.e. you should be measuring as close to the cylinder as possible.

I can't remember how much drop in EGT there is from the headers at the block to the crossover, but 1750 at the crossover would be MUCH hotter at the chamber.

The crossover is where you mount your wideband not EGT.

Rogue_Ant

Maybe, maybe not. Retarded ignition timing and a rich mixture can burn well into the exhaust stroke, causing a high EGT.



Rogue

toddk911

Correct. But my point was in regards to readings at different points. The most accurate is at the header. The reading at the crossover, regardless of what the number is, will be lower than at the header. If you are tuning based on your EGT reading at the crossover, you are in for trouble.

hp18racer

Advancing WOT spark timing 4 degrees in my car dropped the peak EGT I see at the track about 100F. I measure it 1" into the exhaust.

mikjel

Well, my egt dropped 50-70 fahrenheit when richening from 12,7:1 to 11,5-8:1.

Rogue_Ant

Perhaps they dropped because of less knock, thus more ignition timing?



Rogue

333pg333

Man this tuning caper is so involved. So many things impact upon something else. I can see going around in circles is a distinct possibility!

Perry 951

Todd, I'm confused. First you say he is correct about hotter temps in the crossover due to retarded timing, but then you say temps will be lower regardless.

If you have a rich mixture or retarded timing, the fuel will not completly burn in the chamber, and also not likely at the port, it will burn in the availible space in the header, crossover, or the rest of the exhaust. This is evident when you see flames during shift points. The temps during off throttle shifts at the ports is much lower than that in the pipe simply because the fuel is buring in the pipe and not in the chamber.

I use my EGT numbers as a baseline for my car. Each adjustment for fuel or timing will change the reading. Being able to identify peaks and valleys, and know why they happen, is key, not the raw number itself.

Trucho-951

Sometimes a drop in EGT is not a good thing, what measures did you take to ensure that in fact this drop in EGT was not an indication of some degree of detonation. I ask because advancing ignition timing on a forced induction engine while under full boost just seems counterintuitive.

hp18racer

I hooked up a digital counter to KLR pin 15. At 17psi, 100 octane I see almost no knock events. If I go down to about 50% 91, 50% 100 octane at the same boost level, I see dozens of events on every hard acceleration. Watching the knock counter I can figure out what octane I need for any given boost level to be knock safe. If the a/f and knock are behaving, then I'm looking to keep EGT in line with stock number (1650 or less) to not burn up valves.