EGT varience Help

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GM-DR
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EGT varience Help

Post by GM-DR » Tue Feb 20, 2018 7:07 pm

Recently Dyno'ed with EGT Probes---Very Interesting have always used 02 sensors before---anyway forced to use a factory dual plane intake so I had a wide variety of temps #5 cyl was at 1450 and # 1 was at 950---so I tightened the intake lash on #5 by .004 and loosened #1 by .005 (as far as I thought I should go--#5 finished @.006 #1 @ .015) the rest of the cyls were in the 11-1200 deg. range--temps improved on both cyls by over 100deg. and picked up 6hp in the process---later I thought should I have done anything to help using exhaust lash ??? other than a custom cam(not at this time)does anyone have any suggestions ? Thanks in Advance for you thoughts !!! :?

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Re: EGT varience Help

Post by Newold1 » Tue Feb 20, 2018 8:12 pm

When on dynos, especially someone else's dyno one of the big variables is the calibration or condition differences in EGT probes. The age of the probes, the condition and location of the probe bungs and whether they were calibrated as a set when new as well as how much damage and their physical condition differences from previous engine on dyno issues will greatly affect the readings and the accuracy of the readings. When I see big differences cylinder to cylinder right off the bat I move the probes and compare readings to see if the problem moved or greatly shifted. I would not start making big changes in the engine tune and internals until you verify the EGT probes and the dyno are giving you some verifiable accuracy. don't make changes based on possible bad data and numbers! "When in Doubt, Check it Out!"

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Re: EGT varience Help

Post by GM-DR » Tue Feb 20, 2018 8:19 pm

Excellent answer wish I had thought of that !

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Re: EGT varience Help

Post by user-23911 » Wed Feb 21, 2018 1:57 am

Newold1 wrote:
Tue Feb 20, 2018 8:12 pm
When on dynos, especially someone else's dyno one of the big variables is the calibration or condition differences in EGT probes. The age of the probes, the condition and location of the probe bungs and whether they were calibrated as a set when new as well as how much damage and their physical condition differences from previous engine on dyno issues will greatly affect the readings and the accuracy of the readings. When I see big differences cylinder to cylinder right off the bat I move the probes and compare readings to see if the problem moved or greatly shifted. I would not start making big changes in the engine tune and internals until you verify the EGT probes and the dyno are giving you some verifiable accuracy. don't make changes based on possible bad data and numbers! "When in Doubt, Check it Out!"

I was going to write something like that but you beat me to it.

Swap the hottest with the coldest and see what happens.
The protrusion is quite important too.

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Re: EGT varience Help

Post by David Redszus » Sun Feb 25, 2018 3:13 pm

A type K thermocouple has a resistance value of 0.377 ohms per foot for 18 ga wire.
The resistance value for each thermocouple should be the same. If not, the temperature readings will
not be uniform. If the ohm readings do not match the specs, the readings may be uniform but they
will be incorrect.

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Re: EGT varience Help

Post by Rick360 » Sun Feb 25, 2018 6:11 pm

David Redszus wrote:
Sun Feb 25, 2018 3:13 pm
A type K thermocouple has a resistance value of 0.377 ohms per foot for 18 ga wire.
The resistance value for each thermocouple should be the same. If not, the temperature readings will
not be uniform. If the ohm readings do not match the specs, the readings may be uniform but they
will be incorrect.
With any properly designed T/C input circuit (high impedance) the error for any reasonable length thermocouple wire on an engine dyno or in a car would be insignificant (much less than 1 degree) and can be ignored.

I use thermocouples in an industrial environment that have hundreds of feet of wire length and the temp reads the same at the t/c as it does at the data acquisition system input.

Rick

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Re: EGT varience Help

Post by David Redszus » Sun Feb 25, 2018 6:59 pm

For a type K thermocouple, the limits of error are 4.0F deg or 0.75% for the range 530F to 2300F.
For a tip temperature of 2000F deg, this would produce an expected maximum error of 15F deg.

Remember an exhaust gas temperature reading for a pulsed gas flow is never really accurate since
it represents a time weighted average. The gas temperature may actually fluctuate from 600F to
800F and yet display an averaged reading of 1150F.

Also, remember that a thermocouple response time is quite slow, depending on the design.

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Re: EGT varience Help

Post by Newold1 » Mon Feb 26, 2018 10:30 am

This is one reason sometimes with a properly set up and calibrated system a few good steady state dyno pulls are a good way to predict how good the tune really is and how the engine may fare with continued use. The dyno is a great tool if its uses and data are incorporated and do not just establish short pull blasts for bragging rights or disappointments they sometimes provide.

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Re: EGT varience Help

Post by GM-DR » Wed Mar 07, 2018 5:01 pm

Ok anyone who is interested=egt probes were switched during another dyno session(different engine)without a significant temp variance---so is there anything I could have done with existing cam profile using exhaust lash changes ? I have already went as far as I thought I should with the intake lash. Also what about using individual cylinder timing ? Thanks Again !!!

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Re: EGT varience Help

Post by Newold1 » Wed Mar 07, 2018 6:26 pm

I don't think trying to even things up with just lash is a good correction as you don't know if you had a thermocouple error or shift to begin with. I have seen spark timing changes make pretty significant exhaust gas temperature changes, especially if it gets retarded. If your engine is electronic ecm controlled I guess you could make some individual cylinder timing changes but on a standard distributor system I am not sure that's possible unless some of the aftermarket spark control units have that capability.

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Re: EGT varience Help

Post by RW TECH » Thu Mar 08, 2018 12:45 pm

EGT is arguably hardly useful.

On engines with each cylinder lambda laying over top of each other and individual spark trims adjusted to lay CA50 over each other it's not unlikely to see 100°F or more temp variance from cylinder to cylinder.

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Re: EGT varience Help

Post by Newold1 » Thu Mar 08, 2018 4:16 pm

Yes, if everything including tune is working properly and all of the EGT probes are close in calibration. If you are on a dyno and you see cylinders going to 1450 degrees or more consistently , YOU GOT A PROBLEM! especially if you have aluminum heads! What if that nice lambda reading O2 sensor is out of whack! I never assume.

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Re: EGT varience Help

Post by user-23911 » Fri Mar 09, 2018 12:19 am

When I was playing with dual fuel diesels on the dyno we used the EGT as a safety limit.
Or in other words if EGT got higher than XX, shut it down to prevent possible damage.

At the same time, if one of them is cold and it's running a bit rough, that cylinder isn't sharing the load for whatever reason.

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Re: EGT varience Help

Post by David Redszus » Mon Mar 12, 2018 2:01 pm

Newold1 wrote:
Thu Mar 08, 2018 4:16 pm
Yes, if everything including tune is working properly and all of the EGT probes are close in calibration. If you are on a dyno and you see cylinders going to 1450 degrees or more consistently , YOU GOT A PROBLEM! especially if you have aluminum heads! What if that nice lambda reading O2 sensor is out of whack! I never assume.
As EGTs get hotter, piston crown temps get colder and vice versa.

High EGTs indicate a retarded burn which may or may not be due to spark timing.

Low EGTs indicate misfires or very early burn rates and overheated piston crowns.

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Re: EGT varience Help

Post by RW TECH » Mon Mar 12, 2018 2:19 pm

Newold1 wrote:
Thu Mar 08, 2018 4:16 pm
What if that nice lambda reading O2 sensor is out of whack! I never assume.
If you have 8 of them like any dyno tuning shop should have and they all go out of whack at once, you would have an amazing, rare thing happen.

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