EGT gauge question? NEED FAST ANSWER please

mxcale

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Feb 13, 2007
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03 JETTA WAGON
just a 2 1/2" turbo back straight pipe exhaust from GHL and i need to know where to put the bung thingamabobber for the egt gauge. i'd like to know the exact location of where to have that thing welded in on the down pipe. as in aproximatly how far down and if it should be (in acordance to the car) on the front side or maybe back side or left or right? thanks for any help!!!!!!!
 

Fix_Until_Broke

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Most people prefer the EGT on the turbo side - many options here. Search for EGT placement.

I have mine on the downpipe (been too lazy to drill/tap my turbo). I have it on the outside corner at ~45 degrees 'round the bend' from the turbo flange. It points up and to the left (as if you were sitting in the drivers seat). Generally - closer to the tubo is better (both pre and post turbo)
 

jetta-girl

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In the down pipe, as close to the turbo as possible, positioned so that it won't hit the firewall or anything else.:)

Good luck, with it.
 

Locosmotion

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Dont put the bung in the downpipe. The egt will not read correctly. You have to put it in the turbo neck or down the EGR port with an adapter.
 

Monkey1

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All depends on what the egt gauge instructions say. Mine was a autometer and was specific to put it post turbo as it was calibrated for that type of installation.
Also if the probe ever broke, bye bye turbo

Locosmotion said:
Dont put the bung in the downpipe. The egt will not read correctly. You have to put it in the turbo neck or down the EGR port with an adapter.
 

jetta-girl

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Locosmotion said:
Dont put the bung in the downpipe. The egt will not read correctly. You have to put it in the turbo neck or down the EGR port with an adapter.
Yeah, if it's possible that would be ideal. However, I guess it depends on his set up. On my car, we initially planned on installing the bung in the exhaust manifold, but it was way too much work to get to it. :(
 

Matthew_S

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Fix_Until_Broke said:
What makes it read incorrectly in the downpipe? The temp will be lower, but not incorrect I believe.
You can put it in your glove compartment and it will read correctly it just won't give you any useful information.
 

DbLog

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It's not that the reading will be wrong. Pointless would be more accurate. Installing it in the downpipe won't let you know when engine parts start melting. Does anyone know of benefeits having the dung installed in the downpipe as apposed to in the manifold?

Fix_Until_Broke said:
What makes it read incorrectly in the downpipe? The temp will be lower, but not incorrect I believe.
 

Fix_Until_Broke

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Matthew_S said:
You can put it in your glove compartment and it will read correctly it just won't give you any useful information.
Unless you calibrate it for your application against a known reference, it won't be any more/less useful than anywhere else. Mine has been very useful in the downpipe. I plan to put a 2nd one in pre turbo as well to be able to compare the two. We're off topic arguing semantics here.
 

mxcale

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alright alright. if the thing needs to be put in the manifold i'l do it. i thought it was suppose to go after the turbo tho. so now the question is where on the manifold is it suppose to go? does it need to be welded into the manifold or wut is the proper method of installation? pardon me for all the "newb questions".
 

darkscout

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May 28, 2006
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Michigan
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DbLog said:
It's not that the reading will be wrong. Pointless would be more accurate. Installing it in the downpipe won't let you know when engine parts start melting. Does anyone know of benefeits having the dung installed in the downpipe as apposed to in the manifold?
Ding ding ding.

You're cooking a turkey for dinner. You know that the turkey has to be cooked to X degrees for X minutes. You can put your thermostat in 3 locations.

1) IN the turkey. Right up next to where you want to take the reading.
2) In the oven.
3) Stuck to the oven wall.

Now all of the measurements are going to be accurate if you have a good thermometer. All the measurements are going to be able to get you what you need.

1) Take reading.
2) Take reading. Calculate thermal resistance of air in the oven. Calculate radiation / convection heat transfer between turkey surface and thermometer. Calculate thermal resistance of the turkey. Calculate how thick it is to the center of the turkey. Calculate center of turkey
3) All of the above + thermal resistance of the glass front of the oven.

EGT post turbo is going to tell you 1 thing accurately: Temperature post turbo. Unless you get the map lookup of how much heat is being rejected by the turbo, you won't know Pre turbo temps.

Say you have 2 identical engines with 2 identical post turbo temps: 1000F
Engine 1 is cold, the engine isn't even warmed up yet. The turbo is still cold. Meaning that it's rejecting 300F. So preturbo you're actually at 1300F.

Engine 2 is hot. It's in the hottest most part of Death Valley and has just completed a 5 hour straight drive, AC on high. Engine is already as hot as it's going to go so the turbo can only reject 50F, so preturbo you're at 1050F.

Your turbine blades are going to melt at 1200F. Where do you think you'd get more relevant information from? I mean you could always install one pre and post and then make a correlative map based on coolant temp, oil temp, ambient air temp. So you'd have a 2D lookup map, then remove the preturbo (who needs it anymore?). Glance at your post turbo gauge. 1000F. Then pull out your map you made, interpolate between the coolant temp and ambient air temperature on the grid, and ding, you have pre turbo temp.

Go to a Class 8 truck dealer sometime and look at their setups. Cat, Cummins, DDC, MBE, Volvo ALL have their sensors preturbo.

(Numbers were made up for illustrative purposes and not to be regarded as accurate)
 
Last edited:

Street Toys

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I'm pretty sure that you are right that your compressor blades will melt at 1200 degree. Should'nt your intercooler help that? :) That or you should turn your turbo around so you are sending the hot gases through the TURBINE!:rolleyes: That side can withstand a couple of more derees:eek:
 

Suns_PSD

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darkscout said:
Go to a Class 8 truck dealer sometime and look at their setups. Cat, Cummins, DDC, MBE, Volvo ALL have their sensors preturbo.
ALL the Class 8 diesel engine manufacturers install their thermocouples POST-turbo. All of them.

It's true that post turbo the gauge will not react as fast and will typically read anywhere from 100 to 600 degrees cooler depending on heat soak. The truth is that pre turbo you are actually measuring the exhaust gas temps and NOT the metal temps that are important. This is why users commonly go well beyond the recommended egt limits when using a pre-turbo thermocouple w/ no apparent harm. A very hot exhaust stream does not mean the metal itself is actually 2000 degrees or whatever! Otherwise it would have melted long ago.

When you look at the post turbo temps you are allowing the turbo, etc to behave as a heat sink and you are getting a much closer approximation of the temps of the actual metal parts that you are worried about damaging, hence it is a more accurate approximation of when potential engine damage can occur.

As high egts are sustained you will see the post turbo thermocouple and the pre turbo thermocouple get within 100 degrees of each other w/ the post reading cooler since a turbo is actually powered by heat of course.

I have ran both on my PSD (PowerStroke Diesel) and I vastly prefer the post turbo thermocouple configuration mainly because I don't have to spend a bunch of time worrying about the EGT gauge jumping way up and way back down. I only watch it do it's slow climb while towing in the mountains which is the only real time that I might melt it down.

JMHO and it's an unpopular one at that.
 

pellesmil

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Suns_PSD said:
ALL the Class 8 diesel engine manufacturers install their thermocouples POST-turbo. All of them.

It's true that post turbo the gauge will not react as fast and will typically read anywhere from 100 to 600 degrees cooler depending on heat soak. The truth is that pre turbo you are actually measuring the exhaust gas temps and NOT the metal temps that are important. This is why users commonly go well beyond the recommended egt limits when using a pre-turbo thermocouple w/ no apparent harm. A very hot exhaust stream does not mean the metal itself is actually 2000 degrees or whatever! Otherwise it would have melted long ago.

.
How do you know the exact temp entering the turbo with post Turbo loc.
by guessing? (expencive)
by calculating ? (hmmm)
by measuring both? (Hmmm2)

the temp difference is not happening as a result of heat dissapearing into the turbo its rather the fact that building pressure raises temp and lowering pressure lowerers temp. (the temperatur is regenerated into power for running the compressor)
If there is no pressure difference pre/post turbo the temp is equal pre/post turbo. (and no power is feed into the compessor)

The million $ Q is: what pressure difference equals what temp difference? and what temp is actually entering your turbo?

Try that with post turbo probe location
 

pellesmil

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mycruiseagent

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If an Inconel probe is melting you have bigger problems than debris in your turbo! That's a little less than 2600°F. ;)

Mark
 

joevat

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Location
Ont,Canada.
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darkscout said:
Ding ding ding.

You're cooking a turkey for dinner. You know that the turkey has to be cooked to X degrees for X minutes. You can put your thermostat in 3 locations.

1) IN the turkey. Right up next to where you want to take the reading.
2) In the oven.
3) Stuck to the oven wall.

Now all of the measurements are going to be accurate if you have a good thermometer. All the measurements are going to be able to get you what you need.

1) Take reading.
2) Take reading. Calculate thermal resistance of air in the oven. Calculate radiation / convection heat transfer between turkey surface and thermometer. Calculate thermal resistance of the turkey. Calculate how thick it is to the center of the turkey. Calculate center of turkey
3) All of the above + thermal resistance of the glass front of the oven
i was gonna vote for the glove compartment, but this arguement changed my mind.
1 vote for EGT in the turkey!!:D :D :D
 

Suns_PSD

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pellesmil said:
How do you know the exact temp entering the turbo with post Turbo loc.
by guessing? (expencive)
by calculating ? (hmmm)
by measuring both? (Hmmm2)

I don't know? How does every single OEM manufacturer know the exact EGT entering the turbo w/ their POST-TURBO probes. :confused: Cause that is how they all do it.

the temp difference is not happening as a result of heat dissapearing into the turbo its rather the fact that building pressure raises temp and lowering pressure lowerers temp. (the temperatur is regenerated into power for running the compressor)
If there is no pressure difference pre/post turbo the temp is equal pre/post turbo. (and no power is feed into the compessor)

I'm quite familiar w/ the energy used to drive turbos. Thanks though.

The million $ Q is: what pressure difference equals what temp difference? and what temp is actually entering your turbo?

How many diesel motors have you seen melt down due to high EGTs? I've seen a few dozen and I'll give you a hint...the turbos typically were still fine it was the cracked pistons that killed the motors.

Try that with post turbo probe location

Like I said, my opinion is an unpopular one. It's just me and all the diesel engineers over here and all the internet diesel hot-rodders over there!
I specialize in selling Heavy Haul Kenworth trucks. Trucks that haul 200K#'s plus. The egts are often the limiting factor when pulling long grades and the drivers watch the post egt gauge go up and down (much slower than pre gauges go up and down) and they limit them to around 1100-1200 degrees and the motors last a million miles.

I'm not trying to be condescending and I know my opinion on this subject is unpopular. Honestly, if the user of the egt gauge pays attention to the freakin' gauge either way is just fine. You'll just have to get out of the pedal a lot sooner w/ a pre-turbo gauge to be sure.

PS. My PSD currently has it's pyro mounted pre-turbo mainly cause I'm too lazy to switch it back.
 

Doc_Oc

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pellesmil said:
What temp are y seeing at various conditions?
eny dynos done?
Before I put in the 11mm pump the most I saw was 1350 on hot summer days on 200+ kmh. And I mean sustained for few kms.
Otherwise, on steep inclines, in 5 at 120kmh 1150 the most.
And each time, the temp drops back to 450 in less than 10 seconds from 1350 and 5 seconds from around 1000.

Now, with the 11mm and the IQ at 3, the EGT are climbing much faster and higher. I saw 1350 in forth while redlining it. Tonight I just put the IQ to 7.5, cause it was smoking like a mother, the smoke is reduced, but I will get back to you with EGTs. It seamed to be the same as with the lower IQ but I am not sure.
I dynoed the car with the 11mm at 3 IQ and it pulled 141hp. The guy didn't know how to pick the RPM and I have no torque. Also he dynoed in 4th gear if that makes a difference. (pardon my dyno ignorance but it was my first time:) )

Keep in mind that I am running stock IC and IC piping, stock exhaust...stock everything except, 216 Smog nozzles, Stage 2 Unitronic that sustaines 17.5 PSI, EGR cooler delete and 11mm pump. CCV is moded as well but I don't think that matters.
 

joevat

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Doc_Oc said:
I dynoed the car with the 11mm at 3 IQ and it pulled 141hp. The guy didn't know how to pick the RPM and I have no torque. Also he dynoed in 4th gear if that makes a difference. (pardon my dyno ignorance but it was my first time:) )

Keep in mind that I am running stock IC and IC piping, stock exhaust...stock everything except, 216 Smog nozzles, Stage 2 Unitronic that sustaines 17.5 PSI, EGR cooler delete and 11mm pump. CCV is moded as well but I don't think that matters.
141hp with stock IC and exhaust. pretty good but not smart Doc. open up that exhaust and upgrade to a FMIC and maybe then, you'll be able to compete with me........maybe;)

ask JSP how they dynoed Eds supposed 200hp car and how they got torque/rpm readings.
 

Doc_Oc

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Plans are Boostfactory SMIC, and I am waiting for LurkerMike to see how his pipes are coming along. I'll end up with a 2.5" DP and 3" straight pipe exhaust, and as big as it fits IC piping, one way or another.

Well, Joe, you've been ditching me at every GTG I've been so far. :)
And leave JSP alone man. Everybody's on their case. :(
 
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