EGT too high. Exhaust Gas Temperature gauge, gage maximum [merged]

[RuBiCaNT5X]

Forgive the rookie question, but what exactly is the EGT telling you besides the temp of your exhaust? What does higher/lower temps tell you about the status of performance from a tuning point of view. Thanks fellas..

 

[2-0turbo]

Originally posted by RuBiCaNT99GSX
Forgive the rookie question, but what exactly is the EGT telling you besides the temp of your exhaust? What does higher/lower temps tell you about the status of performance from a tuning point of view. Thanks fellas..

This is actually a tough question, misunderstood by many. The only real complication with our cars is forced induction and very short periods of time to really determine the ideal "mixture" or AFR. I'll give the short answer and then expound, if you care to read on.

The short answer to "What exactly is the EGT telling you besides the temp of your exhaust?": nothing, and everything. It is telling you how hot the combustion events inside your engine are occuring. Knowing EGT's and keeping them at a reasonable level will ensure other components (mainly valves and pistons and turbine) do not get too hot and melt. You want to run just on the rich side of the "peak". However, in our cars, you are not going to get even close to this do to knock. You will have to run richer to keep knock at bay. Ask anyone who has tried to tune a turbo car on pump gas with a wideband and the stock ECU. If you try to lean it out to the "right number", you'll get knock, which will retard timing, which will actually cool off the pistons and engine, but make the EGT's skyrocket! Typically, many turbo cars and DSM's for that matter, dump in a lot of extra fuel to keep the EGT's down. This assumes the ignition timing is good. We don't actually burn the fuel, but use if for cooling. Expensive cooling.

To explain this a bit, assume for a minute, we have a naturally aspirated engine. For simplicity, let's assume it is a Lycoming 0-320 in a Cessna 172. The reason I am using an airplane engine for an example is because with a propellor, you can load an engine up to 100% power, or whatever percentage you desire. Using manifold pressure, you can know percentage power very easily.

Assume we are in cruise flight, at 75% power. Nearly every piston airplane has a mixture adjustment knob right on the panel. As you climb, the air density decreases and you must lean your mixture to compensate. Fuel injection handles this automatically for us with a baro sensor.

So, we are cruising along at 5000 feet, we start to lean our mixture. As we slowly screw the vernier adjustment in, the EGT's start to creep up. As you approach your peak (somewhere around 1450F for a NA engine), power and fuel efficiency is maximized. The interesting thing, is that if you continue to lean the engine, the EGT's will start to drop. The peak is important. For a cruise flight, a pilot would typically lean the engine 50 degrees rich of the "peak" on the leanest cylinder. Advanced engine diagnostics allow this.

The problem with turbos is that the induction temp is higher. The air gets heated going through the turbo. Every 1 degree increase in intake temp equals 1 degree increase in EGT (assuming no intercooling). As you increase the boost, the EGT's increase.

It is really hard to tell what your EGT's are telling you on the street. Because of the "bursts" of power we require from our engines, you will never really know which side of the peak you are on unless you can put it on a dyno (this is where O2 sensors come into play). Not a dynojet, inertia dyno, but a brake dyno, one that can apply a load and absorb some heat so you can run your engine at say 75% power for several minutes, adjusting the mixture as you go to find that "peak". The other way to do this would be to drive at high speed and use aerodynamic forces to load up the engine, but tuning and driving fast are not conducive to long life!

This same issue (of not being able to load up the engine) and the "bursts" we usually run, is the lag time in the EGT sensor. Every thermocouple has a time constant, expressed in seconds. Most EGT probes have small time constants, but it takes 5 time constants for the reading to be 97% of the final. You can measure your time constant. With your engine warmed up and with the help of your SAFC, put your foot down to say 10% throttle and hold it there (or whatever value allow a constant RPM without having to play with the gas pedal). The EGT's will start rising. Time how long it takes for the gage to stabilize. That will tell you a lot about what is happening next time you bang through the gears.

I kind of rambled on. This is actually a very complex topic. It is not just understanding the basics of internal combustion engines, but the peculiarties of the DSM engine and how our ECU functions.

 

[RuBiCaNT5X]

I appreciate the effort. That was way more than I expected to get and for that, I am thankful. In conjunction with your post, all I plan on doing is the daily driver thing. I am gonna ask another question, but I don't know if it's answerable and by that I mean pegged to all DSMs or different for each car. I assume as you go up in turbo, your EGT is going to be higher, (more air induced as well as bigger fuel pump, etc..) Is it a feeling out process for each car what temps their exhaust is at? I run stock turbo and stock FP, but when the time comes. Bacially, my question is, how would you know when you are too high in EGT when mods are constantly being added. Bigger IC will result in lower temps becuase the boost temp is lower. OR does it not matter because higher temp boosted air will result in a lower volume of air that gets put into the throttle body. Once combustion occurs, there is less air but at a higher temp. If you added a larger IC and thus were able to force more air into the TB at a lower temp, the volume of air + fuel will be larger and thus create more combustion and more temps. Does the turbo not create enough heat to make a difference in that scenario? What kind of tolerances does the 4G63 engine have at high temps? Lets say, stock EGT is XXXX.XX degrees F, and you add a bunch of mods and whatnot, what HP is the engine going to start decaying from excessive heat, regardless of it's cooling? I saw on a post that someone said a stock 4G63 is good for about 400 HP before you need to replace the internals, but can those internals take it for long periods.. Lets say 5 years of daily drive?

 

[2-0turbo]

Originally posted by RuBiCaNT99GSX, with a little editing by 2-0turbo

1. I assume as you go up in turbo, your EGT is going to be higher, (more air induced as well as bigger fuel pump, etc..)
2. Is it a feeling out process for each car what temps their exhaust is at?
3. How would you know when you are too high in EGT when mods are constantly being added?
4. Bigger IC will result in lower temps becuase the boost temp is lower. OR does it not matter because higher temp boosted air will result in a lower volume of air that gets put into the throttle body.
5. If you added a larger IC and thus were able to force more air into the TB at a lower temp, the volume of air + fuel will be larger and thus create more combustion and more temps.
6. Does the turbo not create enough heat to make a difference in that scenario?
7. What kind of tolerances does the 4G63 engine have at high temps?
8. Lets say, stock EGT is XXXX.XX degrees F, and you add a bunch of mods and whatnot, what HP is the engine going to start decaying from excessive heat, regardless of it's cooling?
9. I saw on a post that someone said a stock 4G63 is good for about 400 HP before you need to replace the internals, but can those internals take it for long periods.. Lets say 5 years of daily drive?

Well, I'll give you one thing, you ask a bunch of questions!
1. No. EGT is not dependant on amount of air, or fuel, but the ratio in which they are mixed. Get a bigger turbo, you'll need bigger injectors to keep up.
2. EGT's are typically limited by the engine components (as in, they will melt if you continue to heat them). Higher than 1650F is asking for trouble.
3. By having a gage and watching it.
4. Yes, bigger (read: more efficient) intercooler will result in reduced EGT's. Every one degree you reduce induction temp, EGT's will fall an equal amount.
5. You were right up till the end. More air + more fuel = more power. That is the secret to HP. Actual, it is not really a secret. Fuel is easy to add, air not so easy since we need roughly 14.7 times more of it than fuel. So, we need big turbos, big cams and good heads to cram that air in there, mix a lot of fuel with it, and light it!
6. Not sure what you are asking.
7. I don't know. Sufficient to prevent metal/metal contact. It is not really an issue if your engine is up to snuff and you are running good oil with good oil pressure.
8. Typically the engine will not start decaying due to heat, but to mechanical stress. I.e. rods, rod bolts, pistons, etc. exceed their yield strength and go plastic. Not good. Thermal stress is an issue, but not really on a street driven car. Your engine is approx. 30% efficient and rejects a large portion of the heat in your gasoline through the radiator. As long as your radiator is large enough, this is not really an issue. You would probably get into problems if you ran 75% power all the time.
9. See Slow boy Racing. One of his customers put down 467 to the wheels on a stock bottom end. Not to say yours won't break at 300, but probably not. 4G63 engines are quite tough and were designed to take far more HP that the 195 they were rated at from the factory. There are plenty of people out there making 400 HP on stock engines. It won't last forever and yes, pushing that much power is shortening its life. How much? I don't know. Who cares, have fun with it.

 

[RuBiCaNT5X]

Yeah, sorry for that assault of questions... But you've done more than your share to edumacate me.. I thank you for that. You didn't quite get what I was asking so I'll elaborate.

1 - Basically you answered my question with your explaination on why mine was wrong. More fuel (bigger injectors + fuel pump) + more air (larger turbo) is gonna = higher EGT.

3 - How do you know that the temps you are at with your injector mods, fuel pump and larger turbo are normal. E.G. Say I have 550cc injectors, 255lph fuel pump and a L1R turbo. What are good EGT's for those mods? 1100F?? 1200F?? I assume boost (psi) and IC piping matter specifically rather than your turbo size.

5 - In the above though, more air + more fuel = more HP = EGT's higher correct?? So in theory, a larger, more efficient IC will result in higher EGTs rather than cooler because you are in fact, able to push more air through to the cumbustion chamber (with larger IC piping and whatnot to support the IC), cooler air = more air in one confined space. We increase the air and thus, mixed with the correct fuel ratio, bigger explosion = hotter exhaust gas.

6 - Now that I reread it, it was a dumb question... Forget about it..


Thanks again for your help...

 

[airbrat]

I have a Greddy EGT w/ peak hold and memory recall (very nice I might add ).

Do you guys know what typical cruising EGT temps should be? This morning coming to work I was about 750-770 celsius. Does this sound about right?

 

[97GSTURBO]

Sounds good. You don't want crusing temps much higher than that, and when you tune you don't want to go over 900.

 

[bubbaGSX]

can anyone tell me the average temp of an egt when its on idle, cruising and freeway? (i have an autometer egt gauge)

the reason i ask this is mine is alil higher that it was before. when i race, i tend to loose my coolant someone help me out

thanks in advance!

 

[92gst]

I think normal is about 1400-1500°F for freeway driving. For my idle, I am at about 800°F or somethin like that. That's what I run, and thats what I was told is normal.

 

[bubbaGSX]

how much were you boosting?

 

[92gst]

i was boosting 11 psi. Was I running too hot?

 

[truwarrior]

5th gear, 55mph 1200 degrees here. idle around 800-900.

If you think it's hotter then usual you could be running rich or lean...depends, but yeah if your wondering what your egt should be to see if it's working right you should be around 1200 degrees not boosting at 55mph in 5th. Atleast that's what my stock 99 is

 

[92gst]

I was running 1400°F while running at about 80 mph.

 

[92gst]

I was running 1400°F while at about 80 mph.

 

[bubbaGSX]

i guess im alrite, im just alil higher temp. idle around 900 and 1400 on freeway.

thanks guys!

 

[e1allen]

before I put on my safc i could wot and get over 1500 degrees if i kept on it. Now with it on, and I had a friend set the settings for me for now till i can get the datalogger, i got up to 130mph and it was sitting at roughly 1350, and it wasnt really climbing. Also the deep exhaust tone, i assume from the timing being pulled before i had the afc is not as bad. i was just wondering if this is a low temp to be running at wot?
it is feeling a little less slugish also.

ported n clipped big 16g

2 1/2" dp 3" back no cat

14psi

stock ic

k&n air filter

 

[anomalyinva]

Im having abit of trouble finding a 1700F EGT gauge that I like. The Autometer ones only goto 1600, but I like them. Will it be enough? And from what I understand I shouldn't run over 1600 anyways, which I don't plan to.

 

[AWDTSiTalon]

I think you just answered your own question.

 

[Vinnie]

I also have the Autometer EGT that only reads 1600F, works great.

1650F it's all about you can go (being on the safe side) you can go higher if you want (at your own risk)

Bottom line, in my opinion that's all you need, I'd ratter be safe than sorry, when I reach 1600F, I shut it down right away.

 

[Blizz92tsi]

I feel really stupid asking this. I got an autometer egt gauge and probe. How high should the readout go? Does it need to read higher than 1600 degrees F ? Thank you for your help.

 

[CYCLONE]

I have the same gauge, my readings are around 1200F
while driving at city speeds. 1400-1450F on the expressway
and about 1550 to 1580 at WOT at the top of 3rd and 4th.

You should run near the 1600 F mark at WOT just make shure
you dont have any knock.

Also make shure your timing is set correctly because it can cause false
readings.

Hope this helps.

 

[TheCrazyDSM'r]

Ok, I have an egt gauge and @ idle is sit around 8-9
when I'm just driving down the road it is like 10-13
on then highway I'm at 11-14
and when I gun it....I haven't gun it yet.
anyways i'm using the S-afc to tune my fuel and I'm running 550's with a 255 fuel pump.
Is this good or am I going to blow something up?

 

[allwheelTSI]

that sounds about right to me.

 

[dave99gst]

me to.
when you gun it it will hit 15-1600

 

[boostmaster]

hey yall, im new to dsms but i recently purchased a 92 tsi w/a 16g turbo 225 walbro, 550s and a small fmic it also came w/a s-afc. ive read all the posts on this subject that i can but i still cant figure out why my egt temps keep going up no matter what i do, i tried turning down the boost, turning up the fuel, and i would change the timing if i knew how(dont laugh, im new remember). it runs good at a cruise (approx 1400 @75mph) but as soon as i go to WOT it jumps to 1600 and will keep climbing if i dont let off. is it supposed to stay at a steady temp while at WOT no matter how long im there. im not trying to have a drag car i just want a dependable car any suggestions? the hi settings on my afc are: 1500/1%,2000/-2%,2500/-10%,3000/-14%,4000/-15%,5000/-17%,6500/-17%. i know the ne points should be different but i cant figure out how to make it let me make changes to the lower rpm ranges. any suggestions would be greatly appreciated.