It is hard to say what the delta should be, but 270F seems a bit excessive. I would want to switch the sensors to see if you get the same readings. There may be some type of calibration issue with one of the sensors. I would use the sensor that is closest to the valve as the reference point. From what I have personally seen and what has been stated as a general rule, you do not want to exceed 1650F when referencing closest to the cylinder head. Rotorary motors will see much higher EGT's, but I would be concerned with your readings. Make a long hard run and shut down the motor, coast to a stop. Pull a plug and see if there are signs of excessive heat. That will also be evident when examing the turbine wheel.

 

Unfortunately I can't switch the sensors... they are different type and have different plugs...

Btw I'm happy if the reference is the sensor closest to the valve... in this case I think I have good values.

Maybe it's the high backpressure at higher rpm to make the turbine intake, where the 4 runners merge into 1, so hot.

I definitely have to remake the ratio test now...



Thanks for the advices.

 

I would tend to think that the Greddy thermocouple and gauge are giving an accurate reading. However, to verify, I would get a hold of(borrow) a temperature reading, digital, multimeter, such as a Fluke.

Test one then the other sensor with the multimeter establishing that both of your monitoring devices are accurate. Do this by disconnecting each of your monitoring devices and hooking the Fluke up to the thermocouple in its place. Tiewrap the Fluke to one of your A/C vents, above the stereo, so that it is readily visible. Then go for a test drive watching the temp readings from each sensor as they cycle. Then do a full throttle run and hit the peak hold button. Compare the max readings to your old readings.

Once you've established that the monitoring devices are accurate, then you've narrowed it down to either one of the 2 sensors. My bet is that your second sensor, the one nearest the turbo is funky because you mentioned that it is slow reacting. So you'll probably have to get a new thermocouple. Good luck...


















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I'd think that the temps would be highest in the combustion chamber and tend to cool down the further it moved out the exhaust tract. I really doubt that EGT's would be hotter at the merge point than they would be in the runners of the manifold

 

Mmmmm... I'm not sure on this, and I'd like to have other opinions...

I understand your point of view, but I still think that the sensor in front of the valve keeps one cylinder temperature, while the other one keep the temperature of all the 4 cylinders...

don't know.... :-D

 

I am absolutely the least qualified to give any sort of definitive explanation for the 270* F. variance in temps between your 2 thermocouples. I just assume, probably incorrectly, that one of the 2 sensors is kaput. I wouldnt think that there could be that marked of a difference between any 2 of the runners on your engine.

1800*+F. is way hot! I don´t see, unless there exists some type of exponential maelstrom furnace theory, why EGT´s from the 4 runners would increase 270* at the point of convergence. Anyway, I am hoping that your engine isnt actually suffering those kinds temps. I hope it is just an egt sensor malfunction.

 

Italian Evo: I did the research and it turns out that indeed you are correct and that the energy of the exhaust pulses of each individual manifold runner combine together in the reduced space of the manifold collector chamber to produce much higher combined exhaust energy, and higher (about 150* F. in the test of a turbocharged Talon engine) aggregate exhaust temperatures.

The same article went on to explain that for tuning purposes, and the longevity of your engine: the temp of the hottest running cylinder with the probe placed in that cylinder´s manifold runner is more desirable, as it gives a closer idea of the true temperature inside the cylinder.

Hope this helps, buddy. I will now definitely book my ticket back to the Newbie Forum....... for a well earned term of self imposed banishment.

 

What can I say.....

Sparky.... you helped me A LOT !!!!!

Thank you very very very VERY much !!!!!!!



Naaaa, stay here, your researches are too important ! :wink:

Bye bye....

 

The individual runners get one exhaust pulse per engine cycle, while the collector gets four. The actual gas temp is higher at the port, but the readings are essentially an average of the temperatures at that location, and the collector has a higher average temp, thus the results noted.

 

Actually, I agree with this. I would venture to guess that the reason the merging part seems hotter is because the metal to which the probes are mounted is cooling the probes themselves. The metal next to the head, and the metal which has less mass of exhaust gas flowing through it, will be more easily cooled by the surroundsings and the head itself. (through the gasket)

I see no scientific basis for the collector region having hotter exhaust gas. That would imply that the exhaust gas actually increased in temperature as it moved from the engine to the collector. Where did this heat come from?

Since there is no heat source other than the engine itself, I cannot see any reason for the real exhaust gas temperature to increase. The probes must have been reading incorrectly.

-Adrian

p.s. Remember: EGT probes don't actually measure exhaust gas temperature- they measure their OWN temperature, which we are assuming to be the same as the exhaust gas itself.

 

I am still serving out a penitence as a result of my original argument, SaabTuner. I was hoping that this thread would kinda die out quietly, 'cause I really stuck my foot in it and ventured beyond the modest bounds of my limited knowledge. And now, I'm about to do it again:

We are correct when stating that the temperatures inside the combustion chamber and specifically the temperature of the piston crown will be the hottest. The hot exhaust gases exit the combustion chamber via the exhaust ports and through the 4 separate exhaust manifold runners before combining at the merge collector.

This exhaust energy travels in the form of pulsations. Initially, w/i each individual runner, the exhaust pulses are spaced relatively far apart. Or one pulse per combustion cycle. An exhaust probe placed w/i one of the runners gives an average temp with an exhaust event followed by a cooler lapse until the next exhaust pulse comes roaring down the runner.

Where things get interesting is when these individual, intermittent pulses from each separate runner all combine within the restricted confines of the merge collector. Once inside the collector, the pulses are no longer separate, isolated pulsations, . In fact, they combine to become one continuous energy flow, compounded by the natural bottleneck (backpressure) created by the turbine housing's reduced scroll space.

Additionally, the gases at this point have slowed and become resident gases within the collector and have more time to transfer heat within the confines of the collector chamber. A temperature probe placed inside the merge collector reads the aggregate temperature of all the runners combined, with no cooling lapses between exhaust pulsations.

Tuners prefer to use the temperature captured from the exhaust manifold runner of the hottest running cylinder because it more closely indicates the actual temperature within that hottest running cylinder. Whereas, the temperature captured at the merge collector tends to run at least 150*F. hotter than the temp of the hottest running exhaust manifold runner. Tuners have to tune to the hottest running cylinder.

This was my long winded attempt to agree with what CO VR4 already explained above.

Edited for grammatical effect.

Edited a second time to enhance explantion. Hope this clears things up. Feel free to add or dispute any of these claims. As I said, I really stuck my foot in it now.

 

Just look at the colors along exhaust tract in heavy use and you can see the collector really is hotter for reasons stated by others.

 

Exactly !

I saw in another post that you have some backpressure:intake numbers ?

Could you post them ?

 

shaun, do you have any figures then what is a comparable figure to see at the collector ??

I have my EGT probe hooked up at the collector and I consistently see 900+C .. and on shifts I can see as high as 950C! everywhere tells me I'm running too high an EGT

As for the original intent of this post, non conclusive layman .. italianEvo.. there's a post somewhere from ludikraut that showed a change from .63AR to a .82AR showed a dramatic increase in power without loss in spool .. which may explain the backpressure issue that you (and me ) are facing.. ie car not making power even as you crank up the boost ..

 

Italian EVO's high EGT problem was largely due to an improper tune, specifically, using too much ignition timing retard to accomodate a boost level that was too high for the fuel octane.

There may be several reasons why your EGT are too high, and 950C is indeed very high. Without knowing specifics of your setup, one can only guess.