Share some EGT's Please!
 

So I finally got an EGT installed (Glowshift). I know the temperature sender "should" be installed in the exhaust manifold itself, but was reluctant to punch a hole in a cast iron piece. Instead it's located just after the manifold/midpipe mounting flange and just in front of a high-flow cat. Fully warm and cruising on the highway at 73 mph, (~3600 rpm in 6th) it's reading 880 deg F (470 C). In some limited thrashing I saw 980 F (525 C). The readings are much lower than I was conditioned to expect. I'd like to hear from others with EGT gauges what they are seeing, under what conditions, and where their sensor mounting point is, so I have some idea if my gauge is working properly. Thanks!

following with interest
OD

kinda lonely in here hey OD?

roughly 1500 - 1600 degF WOT at the exhaust port

Thanks. I wonder if it's reasonable to see a ~500 deg F drop in temp going from the exhaust port location to the cat entrance. Since the normal max operating temperature is 1200-1600 F (for ceramic cats) I wonder what's really causing cat failures.

Ok, I'll play.

My scanguage II says about 850 to 950 on my 07 6spd auto when driving easy to driving hard.

I thought it was showing cat temp, although it seemed low for that so I guess it's really EGT.

I don't think you needed to install a sensor for it since there's already one on computer.

Something is wrong with the gauge I think.

I have mine mounted in the same location (turbo downpipe) and I eradily see 1200-1400 F on the highway.

what the scangauge shows is the cat temp(signal from secobary O2 sensor). thats inline with what i see (in Celcius) with a gutted cat. though i have made it to nearly 1000 a few times

So then, the Scanguage is fairly accurate to watch for CAT meltdown, eh?

Typically EGT is measured as close to the actual exhaust port as possible. The idea (like capturing water and oil temps) is to capture the highest possible readings that the the oil, water or exhaust system are seeing.

We have seen 1,700F at .93 Lambda at WOT under engine load. This is measured approx 2-3" off both the forward and rear exhaust ports. During our 50 minute races we typically we 1,500-1,650F at .89 Lambda.

You should find that driving up a steep hill in 3rd or 4th gear will result in higher temps than "flooring" it on a level road.

Hope that helps.

Is that about where the cat would be or further upstream?

Just upstream... so think of it like where the cat joins the manifold. Right there.

Thanks! The more data points, the better.

Agreed that close up is normal location. I put it near the upper end of the midpipe for two reasons (a) unwilling risk putting a bung in the the cast iron manifold (no problem to do with ss headers), and (b) was wanting to see what the cat inlet temp was reading to avoid melt-ation.

I am struggling to reconcile the readings I'm getting with those of others. It could be that:

a) My gauge is just reading wrong, or (b) it's really reading in deg C. A couple things indicate perhaps that it's not too wrong. First is that it takes only a couple of minutes or so of idle or slow running for the gauge to read 400. This is consisitent with the cat "light off" temperature of about 400 degF and the general wisdom of cold starts (and the aux air pump operation). This would not be consistent with a reading of 400 deg C (700 deg F) which would imply a much quicker "light off".

b) The OBDII reading is "high". Assuming that the OBDII reading is coming from the rear O2 sensor, that one is located in stock form, *after* the first cat element. The chemical reactions inside the cat will raise EGT by 100-400 deg F (55-225 deg C), so my reading will be correspondingly lower since it's *ahead* of the cat.

c) There really is a ~600-700 deg F (330-380 deg C) drop in EGT from the upper manifold to the entrance of the mid-pipe. It seem like a lot, but I think it's possible. I did a back-of-the-envelope calculation to look at the radiative cooling rate using the Stefan-Boltzman law. I estimated the area of the manifold piping to be 0.3 m^2, its heat to be 1140 K the temperature of the surrounding enviroment to be 350 K, and an emissivity of 1. The energy of the heat radiation basically goes as the 4th power of the temperature. Plugging and chugging gives a pipe radiating 28 kW (38 hp) of heat! This is the upper limit, since I assumed a temperature for the whole pipe to be that of the upper header. Assuming my low ~1000 deg F (830 deg K) reading at the back of the pipe for the whole pipe, one comes up with 8 kW of heat being radiated away as a lower limit. With some more numbers (mass flow, flow velocity, etc) one could probably get a good estimate for the temperature drop in this region - expect it's substantial however.

Might take some more detailed measurements to sort it out though. Maybe during the winter, I can make some attempt to check my present gauge's calibration with a torch and an IR pyrometer.

a) This is normal

b) The 02 is heated so it will always have an approximate mininum temp

c) wow.

Do you tune your own engine / do you have the opportunity to do so? I think you'd find some interesting results by playing w your A/F.

Congrats to you for measuring. Measuring is the hot ticket.

a) Yeah, calibration is a PIA. Only one of the half-dozen pressure/temp gauge/sender combinations I've tried gave decent results right of on the box. Plus *none* worked even close without running a separate ground wire from the sender back directly to the ground for the gauge inside the cabin.

b) I haven't looked much at the temp reading from the O2 sender. The GlowShift EGT gauge has a minimum temp reading of 390. Most (inexpensive) temperature senders are not linear in their response and the gauge calibrations are based on a straight line. The slope and offset of the line used are chosen to be most accurate in their "normal" operating range, so (without checking) I wouldn't trust a "good" EGT at 400 F +-50 deg, even if it's dead on at 1700 F.

c) If the EGT at WOT were 100 C vs. 1000 C, we'd have our ~400 na hp.

I eventually want to play with my own engine tuning, just have to find time to read the 1000 pages on the Engine Tuning forum. :banghead: I want one tune for ~200 dyno hp, and another for 25 mpg :lol:

Reading up on cat operation, it occurs to me that having an EGT probe (calibrated) at both the cat entrance and exit might be useful. (Or set up a little differential volt meter between the two probes.) The temp rise across the cat is a measure of how hard it's working. Lean ~ small rise, Rich ~ large rise, to a first approximation. However, the real effect depends on a bunch of other factors - perhaps those multiple effects contain information useful for tuning, dunno. It already seems to me that the legend of high exhaust temps killing the cats, is only indirectly true. The inlet temp seems too low to do it alone. The killer is a rich mixture results in a big rise (up to 500 deg F) within the cat, that then sends it into fry-land.

ignition? makes a huge difference. theres a person or two here who could probably guess within a small margin from experience, but understanding the the 3-way relationship between A/F, Ign, EGT is essential for someone wanting to use EGT for anything more than just a pretty light/dial. which fwiw is why I see EGT as nearly useless for anyone who is not actively tuning and well aware of what they are doing

there is no need for 2 calibrations to do that.
As an addendum to that(but not the basis for that statement), I have not been on a dyno but by all rights, considering timing, fueling, tested compression, accurate MAF readings, comparison, etc, I should be right at the 200 mark. And I have no problem making 25-26mpg at 70-75mph, have even hit 27mpg.

There is some truth to that, but the flip side is that in removing the excess fueling, and putting ignition where it should be, you again start reaching the range where the cat wont live long

I see where you're coming from, but rather disagree. First, and foremost I put it in out of curiosity. If you state people need to be well aware of what they are doing, how does one achieve that awareness without information? Yes of course, one can read up on the subject and that is useful. However, popular sources in the form of books and forums are also full of incorrect "information". The best way to seperate truth from fiction is by experiment and observation. Observation requires instrumentation.

Second, an EGT helps in monitoring the state of one's engine. How useful is an oil pressure gauge? No hp or mpg is gained as a result of having one, yet it's generally regarded as useful anyway.

Third, in my airplane experience, an EGT was a vital instrument in monitoring and optimizing engine operation. Why is it not so with cars? Does it contain information that is not otherwise available with the more conventional car-tuning? (I don't know the answers to these questions and this thread is part of a process to find out the answers.)

Overall, the smartest thing to do with an RX-8 is to upgrade the stereo and leave everything else alone - but that wouldn't be any fun would it?

That's why I put in a $99 metal-substrate cat and put the $1200 stocker in a nice safe-from-my-experiments place on a shelf. We'll see if the el-cheapo version survives. :SHOCKED:

I should have said it a bit differently to be clear. this is how it should have read:

which fwiw is why I see EGT as nearly useless for anyone who is not actively tuning and well aware of what they are doing, or using it as a part of the learning curve to become aware of what the readings really mean

I dont disagree with your approach at all. I totally agree with you on the points about freely availible information and personal experience. What I said was only meant in the sense of the bandwagoning where a bunch of guys, with no clue what it means and no intent on learning anything or doing any tuning, decide collectively out of their own ignorance that EGT monitoring is needed.

Absolutely agree with you on point 2 also. Though many of the other common things to monitor are simpler to understand. ie the oil pressure, most people know that it simply should stay within certain ranges, anything else indicates a problem they need to have fixed. While EGT can be used in this manner also, the relationship of EGT being tied to ignition AND A/F which are rarely ever(never) exactly the same for any 2 modified vehicles, doesnt lend itself to someone just reading that XX-XX is acceptable normal range for the gauge to read. (Port timing would be yet another factor that would further complicate a good understanding, but in our case obvisously is a non issue unless you have had port work done)

I dont have any insight into airplane motors, but I imagine that given the conditions they operate in(altitude/PPO2, etc) that it would indeed be a valuable tool to have, I could see this being even more important in turbine engines. Still yet, one monitoring the gauge(s) would have to at least know what readings are abnormal for given engine conditions - something I would assume is a part of training/qualification to pilot?

Good idea, especially if you're wanting to experiment not just for learnings sake, but hoping to find a happy place in your tuning where you can put the stocker back permanently :)

Cool: :grouphug:

I did a rather long (and generally unread) detailed exposition on aircraft engine management in the pressure vs flow thread starting around here: https://www.rx8club.com/showpost.php...&postcount=205

Trying to simplify, and in terms of EGT, the a/f is often optimized by the pilot via the reponse seen to mixture changes on the EGT. Prior to 1990 or so, all engine management systems for light airplane piston engines were both manual (pilot-controlled) and mechanical. (Old, not-so-bold pilots have a deep distrust of electrons since they tend to stop moving at awkward times.) Unlike cars, acft engines experience a wildly variable pressure environment from changes in altitude which require significant changes in fuel metering to keep them running right. But a plus, relative to cars, is that a typical flight has rather few throttle adjustments: idle, full open (takeoff), cruise/climb, cruise, and descent.

To simplify: suppose one has a full power takeoff, climbs to 5500 feet, levels off, reduces power, and stabilizes at a steady speed. What's next? While the engine will run this way, it's sucking gas like crazy because the mixture is very rich. If the propeller has a fixed pitch, finding the right setting for the mixture is simple: start pulling out the mixture knob thus "leaning" the a/f. As the mixture gets closer to optimum, the rpm increases, peaks, then starts to fall. The peak value is the optimum "best power" setting for the cruise condition (which is on the rich side of lambda=1). For lowest fuel consumption, pull it out a bit more. Too far and the engine will "stumble". Push it back in just a little until the engine runs smooth and that's a good setting.

The EGT comes into play if the propeller is "constant speed" which means the pitch adjust itself to maintain an rpm that the pilot chooses (with another knob). Now, from the full rich condition, as the mixture is leaned, the rpm stays constant, but the EGT rises. Lean the mixture as before, but note where the EGT peaks. This becomes the reference point for further settings. The operating manual will tell you where to set the mixture for minimum fuel consumption within safe limits. I'm rusty, but it's 50-100 deg F on the "lean" side of the peak. Note to users: "leaning" here is giving *lower* EGT's. Rich = cool, lean = hot, is simply not true. Note also, that, assuming a healthy engine, the absolute value of the temperature is irrevalent, only the relative one as changes are made.

As far as diagnosis is concerned, that function comes into play when there are probes on each cylinder exhaust pipe (most airplanes have "headers", not "manifolds"). Equipped that way, one finds that each cylinder behaves somewhat differently; each is running slightly "rich" or "lean" relative to the others, but only slightly. When something starts to go bad in one cylinder, that spread will increase, often without any other obvious indication. Suppose one of your two spark plugs/cylinder goes bad. The engine as a whole runs fine because the other one is still working. However, the EGT for that cylinder will shift markedly because of the now unburned fuel coming out. The same kind of thing will happen if you break a piston ring or burn an exhaust valve.

With turbocharging, another EGT probe is used right in front of the turbocharger, but called the Turbine (or Turbo) Inlet Temperature: TIT (yeah I know). Here the absolute value matters - too high and you fry the turbo. It can go high from your mixture adjustments, or from too much back pressure due to a mechanical issue with the turbo or a mishandled waste gate contoller or a misbehaving pop-off valve.

Anyway - hence my curiousity about EGT use in cars.

wouldnt egt temps vary in a car due to frequent throttle modulation?
I think i understand what you are saying about the usefulness of this measuement.
I suggest a vacuum gauge a good bit and get blank stares.
OD

Oh yeah they would. To find the peak egt as described above, but in a car on the street would be pretty impossible. It would be possible on a dyno, but time- and money-consuming. Comparing two different fuel maps under reasonably similar conditions would be doable if the egt info could be logged along with the other stuff.

More practical perhaps is for me to buy a second identical sensor and locate that one after the cat. I could put it on a switch to the one gauge and look at not only the cat inlet temp, but the temperature rise I'm getting across the cat. Even better would be to "calculate" (with some analogue electronics), that rise and display it seperately. That way, I can play around with the fuel maps while noting areas of engine operation where the temps are getting out of hand and adjust (offline) the a/f accordingly. At a second level, assuming I know what the danger areas are, I could trigger water/meth injection to bring them to safe levels while still keeping the a/f in a range that maximizes either power or efficiency. Trigger on EGT info, rather than MAF in other words.

Aaargh! :spank: Manifold pressure, not vacuum! :kiss: