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Discussion Starter · #1 ·
okay so when I floor it and its at WOT climbing through 4th i REALLY doubt that exhaust temperatures are taking 10 seconds to reach their final value, but thats what my autometer egt gauge says.

i would think the exhaust gas stream would instantly reach its new temperature based on the air fuel ratio, just like when you adjust an acetylene torch mixture it instantly changes temperature.

the problem is the EGT probe is 3/16" diameter and is passed into the exhaust manifold runner via a brass fitting, which it fits into very snugly. this means that the probe is ALSO measuring the exhaust manifold temperature, which i am sure changes much more slowly than the actual exhaust GAS temperature, and is what is probably slowing down the response of the probe, along with the probes relatively LARGE mass

what is needed is a MUCH smaller probe, which is passed into the exhaust manifold with some kind of insulating material like a ceramic or asbestos to greatly increase the thermal resistance between the probe and exhaust manifold.

any ideas?

i think some kind of asbestos tube for the probe to pass through "captured" inside a brass fitting with a through-hole screw on lid might work, along with a 1/8" or smaller probe
 

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It is more than likely the gauge, not the probe...about all the probes are alike, but the gauges can read temp as little as once or twice per second while others can read 100 times per second.
 

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Somethings not working right if it takes ten seconds to respond. could be placement, bad engine tune, bad gauge or thermocouple.
I had a bad westec gauge that was slow and didn't read correctly.
 

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Discussion Starter · #7 ·
all probes are absolutely NOT alike. a bare tip probe with an exposed junction will have a sub-second response time (like the one puppet posted) while a 3/16" probe like I am using will have a multi-second response time. check out mcmaster.com in the thermocouple section for a list of probes and their associated response times.

plus, like i said, the fact that the probe that came with my autometer gauge is in direct contact (and for about 1/2" of its length) with the METAL exhaust manifold which has a MUCH lower thermal resistance than the exhaust GASES, what I have is an EMT probe...exhaust MANIFOLD temperature probe

for instance: I get my egts up to 1500F then let off the gas and put it in neutral...the gauge still reads 1500F and takes about 5 seconds to get down to 1300F...im ABSOLUTELY sure my exhaust gas temperatures arent anywhere NEAR that IMMEDIATELY after i take my foot off the gas
 

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Well like I said before if it takes a long time to respond then theres something wrong because ive seen more than one egt gauge and they dont take more than a second to do anything, that is the same probe that comes with the zeitronix afr meter and you will need a digtal gauge to take advantage of it.

Why would your gauge keep climbing after youve let off the gas ? mine drops immediately makes no sense and changing probes is just waisting money
 

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you could certainly run an exposed junction probe, but it would last about an hour. thats the tradeoff you have to make, response time vs longevity.
 

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all probes are absolutely NOT alike. a bare tip probe with an exposed junction will have a sub-second response time (like the one puppet posted) while a 3/16" probe like I am using will have a multi-second response time. check out mcmaster.com in the thermocouple section for a list of probes and their associated response times.

plus, like i said, the fact that the probe that came with my autometer gauge is in direct contact (and for about 1/2" of its length) with the METAL exhaust manifold which has a MUCH lower thermal resistance than the exhaust GASES, what I have is an EMT probe...exhaust MANIFOLD temperature probe

for instance: I get my egts up to 1500F then let off the gas and put it in neutral...the gauge still reads 1500F and takes about 5 seconds to get down to 1300F...im ABSOLUTELY sure my exhaust gas temperatures arent anywhere NEAR that IMMEDIATELY after i take my foot off the gas
OK...I stand corrected on the probes, just all of the ones I have used myself were alike...A EGT temp will drop immediately when no longer at WOT. I only use large digital units so I can see the temps at a glance and they have a memory of highest EGT during the pass, or lap...until reset or shut off.
 

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Why are you guys so worried about egt's anyways?? Egt gauges should be glanced at after the wide band. Mine reads slow and I don't give a damn, my wide band is instant, and so is my knock sensor. Those 2 are more important than a egt. Egt's just back up what the wide band and knock sensors are telling me.
 

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JMVegas, how do you visualize the knock sensor output? sounds like a good way to go, too. i know that we all, but especially me, keep learning new stuff every day :)
[offtopic]
i have a zeitronix wideband system kicking around, but dont have a gauge for it yet.. could i hook up my narrowband gauge to the analog output port?[/offtopic]
thanks
 

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Discussion Starter · #19 ·
wow...i have some juicy things on this topic:

first off, this article is CHOCK full of grade-a info on egt probe and gauge response times. this guy took several probes and measured their response time without a gauge, then took a bunch of gauges and measured their response time with a fixed input voltage. VERY interesting.

http://www.turbodieselregister.com/EGT_EVAL.pdf

second, the teamrip.com exposed tip EGT gauge seems to be impossible to get. those people never answer the phone or email in more than a week. so I bought one from here instead:

EGT Gages

its got a 12' cable. kinda expensive at 79$ + s/h but oh well

seems like quite a few people sell exposed tip egts gauges..just google "exposed egt probe" and you will get lots of hits

I think an engines EGT provides valuable info for tuning and diagnostics, and as a warning to transient problems that could lead to severe damage. I'm pretty sure you could have excessively high EGT's even with a good AFR and no knock. Plus I don't want any gauges in my car that are useless, and right now my $150 autometer EGT gauge and probe are worthless for seeing anything at WOT.
 

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wow that's a bunch of NICE infos right there. thanks for digging into that and sharing this with us. needs some reading though :)

anyways, as i have a zeitronix system that also supports EGT i'm also in the progress of choosing a probe.
on the zeitronix site they have one for 85$ which they claim very fast (of course, lol) and this are the more specific infos i got as a reply via email:
T/C going from 0 to 100 C, it will take approx. .40 seconds to reach 66.66 C, .40 seconds more to get to
88.88 C and .40 seconds more to get to 96.29 C and so on for a total of 7
time constants to reach 100% of the change. This means that to see the
settled temp at 100 C it would take a total 2.8 seconds for the total 7 time
constants at .40 seconds each. Realistically, you are at 96.29% of the step
change in 3 time constants or 1.2 seconds.

In other words this is very low mass and fast EGT probe.
any opinions on this? i'm a bit confused about the numbers :D might be helpful for somebody looking into buying a zt-2 and thinking about their EGT probe (8' cable) as well. as said, 85$ + s/h is still kinda daylight robbery, but i havent compared it to other probes by the # yet. so it might be still worth getting this one while your at ordering your zt-2 anyway.

maybe someone on TD has this probe in use and has some comments for us :thumb: otherwise, any comments on the #s?
i will also have a look at the rjc site.

thanks
 
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