VaporTrail

There is a gross amount of misinformation floating around about exhaust gas temperatures. I have posted many times explanations to EGT questions. But it seems the search feature here tends to overlook them for whatever reason. I have found an excellent article done by the fine folks over at Simple Digital Systems. It is written in plain English, and is 100% correct. The link is http://www.sdsefi.com/techegt.htm and for those of you that are lazy to click, read below and learn!

There seems to be a lot of mystery and misinformation about using exhaust gas temperatures to tune engines. Claims by many EGT gauge manufacturers about it being the best way to tune an engine must be qualified. The BEST way to tune an engine is on the dyno- PERIOD. What EGT is good for is a reference for where the engine made maximum torque at wide open throttle. Once removed from the dyno, a similar air/fuel ratio can be established a later date by dialing in the mixture to achieve the target EGT. It is really the AFR that is important, not the EGT. Most engines will make maximum power at an AFR of between 11.8 and 13 to 1 however, the EGT may vary from 1250F to 1800F and is dependent on many factors.

It should be mentioned that the target EGT is valid only on the same engine configuration as was used on the dyno. If you change the ignition timing, cams, pistons, headers etc., the optimum EGT may also change. Raising the compression ratio with no other changes will drop the EGT at the same AFR. Retarding the ignition timing will generally raise the EGT at the same AFR. One engine might make best power at 1350 degrees while a very similar engine might be happier at 1500. You can't guess at this or you are simply wasting your money on the instrumentation. Wankel engines have higher EGTs than comparable piston engines due to their lower thermal efficiencies. 1800F is not uncommon here.

Some gauge manufacturers say you should tune to achieve maximum or peak EGT for maximum performance. This is incorrect. Peak EGT generally occurs at an AFR of around 14.7- 15.0 to 1 on gasoline. This is far too lean for maximum power and is dangerous under continuous WOT conditions. Many people think that the leaner you go, the higher the EGT gets. This is also incorrect. Peak EGT occurs at stoichiometry- about 15 to 1 for our purposes. If you go richer than 15 to 1, EGT will drop and if you go leaner than 15 to 1 EGT will ALSO drop. It is VERY important to know which side of peak EGT you are on before making adjustments. It is safe to say that peak power will occur at an EGT somewhat colder than peak EGT.

You can sometimes feel a lean of peak condition as the mixture is hard to ignite and power will be down a bit as well. Once the AFR gets close to 17 to 1 at WOT, generally the engine will start to lean misfire. Most tuners always recommend to begin jetting or programming from a known very rich initial setting and carefully leaning until torque falls off slightly, then going back richer to the point of max torque. Note the EGT at this setting. Be aware that altitude, barometric pressure and ambient air temperature may affect this optimal temperature to some degree.

Are EGT gauges better than AFR meters? Conventional narrow band oxygen sensors and digital LED meters are not the best devices to measure AFR in the richer ranges but they certainly warn of a too lean condition immediately and obviously, without translation by the driver and they are affordable. Meters combined with wide band sensors are laboratory quality usually, highly accurate and useful but very expensive and sometimes bulky. EGT gauges have the limitations above and are generally priced between the other two. I would suggest that the two types are complimentary. EGT gauges have the advantage of working long term with leaded fuel which will clog oxygen sensors. EGT gauges are widely used to set mixture on engines used for steady state high power applications where operation has been carefully documented such as in aircraft. The choice would depend on the application. Both are better if you can afford them.

All this is courtesy and copyrighted by Simple Digital Systems EFI http://www.sdsefi.com

Somebody please put this in some sort of archive

1fstevo

I have read the techedge article already to find the information, thanks for posting.
My question is:

Let's say the A/F ratio is at 12.5:1 full throttle 7500 rpm constant. The mixture is perfect but EGT temp. can change due to timing event. Generally, what temp. do you see at this example on honda engine? Maybe it's not enough information but due to lack of dyno access and experience maybe you can explain much better on how is too retarded or too advanced effecting the EGT temp.
I know that generally, correct advanced timing ( say 35-40 degree of timing) will lower the egt. overly retarded timing will rise the EGT.

On a boosted honda with around 10psi full throttle near redline of 8200, what temperture you usually see that is optiumal?


[Modified by [Evo]Hybrid, 10:40 AM 8/8/2002]


[Modified by [Evo]Hybrid, 10:45 AM 8/8/2002]

rjardy

thank you


right click save


Rob

VaporTrail

boosted Honda is far too vague. As stated in the article, EGT can change with barometric pressure, engine and air temperature, compression ratio, cam choice, cam timing, and many other factors. What should be most important to you is that the air fuel ratio is correct and safe, and the ignition advance is within safe parameters of your known combination. This is where tuning experience pays off. So, I retort your question with another - which boosted Honda in particular?

1fstevo

9:1 compression B18C1.
Stock cam, stock camgear setting.
stock distributor timing at 16 degree.
On the ignition map, I set low rpm city driving mode around 35-37 degree of advance.
At 8psi 8000 rpm I set the timing at 25 degree of advance. Timing increase as it decreasing boost.

All I'm saying is generally, what temp. you usually like to see? 700 celius? 800 celius? I don't think I would want to see anything above 850-900 but who knows. I think 700 is alittle low.


[Modified by [Evo]Hybrid, 10:51 AM 8/8/2002]


[Modified by [Evo]Hybrid, 10:53 AM 8/8/2002]

Arturbo

Click on this----->
Keep this in your note pad!

1fstevo

LOL

VaporTrail

now I ask you another question - where is the EGT probe tapped? Location is another big factor, as a movement of only 4 inches can drop the EGT reading dramatically. I usually keep them in the manifold, close to the head, and have seen 1000 deg celcius without a failure.

1fstevo

#1 cylinder on the manifold one inch away from the head.
Holy ****!!! 1000 celius? Wow, my greddy egt gauge turn red mark as pass 900.


[Modified by [Evo]Hybrid, 11:02 AM 8/8/2002]

VaporTrail

read above post

1fstevo

okay, 1000 celius is probably too big ***** for me. Any other suggestion for a safe boosting day?

VaporTrail

my question is, why is that too big ***** for you? Again, there are so many variables that go in to EGT's. What you should be most concerned with is pre ignition, detonation, and air/fuel ratio. Use EGT's as a reference, not as a guide.

1fstevo

I understand there is other variables but truthfully at that temperture I wouldn't buy it. Above 900 degree celius is pretty much melting stage and I wouldn't recommend that to anyone. You are telling me that beside 1000 degree, there is no other average temperture that you like?

I have no detonation or preignition and my wide band is also showing around 12.5 A/F. We all know how A/F should behave like but EGT temp. is sometimes very mysteries.


[Modified by [Evo]Hybrid, 11:13 AM 8/8/2002]

VaporTrail

Every car is different. Some like it hot...some don't. The point of this article and thread was to show you how to use EGTs, and to show you how uncomparable they are.

1fstevo

Okay, let's just leave it here. I thought you were actually going to give me a suggestion but nevertheless, tuning secret is tuning secret. Actually I never asked for tuning secret just a average temperture that you see which you like since you should tune quite a few cars on the dyno if I'm correct. I need not to debate over theories but actually just want to share a few experiences. Thanx for your help anyway.

BTW, EGT is important. Beside dyno for torque amount, EGT will tell you if your timing is correct at a certain degree. A/F of coarse is first prioty.


[Modified by [Evo]Hybrid, 11:23 AM 8/8/2002]

Arturbo

Ok, the variables depent on Air to fuel, fuel used(gasoline, butane, propane), octane, and compression.
Now, What I think you are asking is; what is the egt temp at X amount air to fuel? Right?

shadowdawn

I already understood and knew some of what that article was talking about, but thank you for informing us again and to those who didn't know.

My egt is tapped in the dp at the VERY top where it meets the turbo.... highest temp I've seen is 880c during a highway sprint in 3rd gear climbing to redline.... it was scary I must've been leaning out at the time. Had stock timing, inline pump, stock injectors, stock fuel pump, 12:1 fmu, and thats it

A friend running the AFC hack his temps don't go above 810c and we essentially have the exact same car only 4 years apart

KC GSR

After reading that article I feel that spending $160 for an EGT gauge is a complete waste of money for me. But my mani is already tapped for one. All I want to be able to do is make sure that my A/F ratio is where it should be. If my EGTs are going to change due to an infinite amount of variables that tells me absolutely nothing. I need something that will help me be able to properly tune my VAFC to rich or lean out my fuel mixture (dont have an A/F gauge) and it sounds to me like spending $160 for an EGT gauge isn't the answer.

prophet

basically thats what it sounds like..the only thing that can save your engine is that never run the car hotter than what it is at stoich....

KC GSR

so basically since my mani is already tapped i get to spend $160 on a gauge for looks.

ccjb100

Why can't you just plug the tapped hole??

KC GSR

i guess i can, just have a muffler shop weld something over the top of it?

2000Accord5sp

Forgive me if this is a stupid question as I never really knew what EGT's are. From reading this, it would seem to me that a whole lot of other factors can come into play, such as how good your cooling system is? For instance, if your IC isn't cooling the air good enough, that in turn would cause higher EGT's won't it? Or am I missing the point?

lucas569

buying a egt gauge is not unimportant, its a good tool to use when combined w/ an a/f gauge.

KC GSR

is the greddy A/F gauge better than the Autometer or do they both suck mainly because they aren't wideband?