Placement of sender probe for EGT

[GBrowne]

Hi, further to my investigation on this topic, what is the group's concensus on placement of the EGT probe sensor: pre or post turbo?

The logic of pre turbo is that it will record the (dangerously high) temps prior to being 'lost' by the turbo (as turbos will reduce the temperature by a set percentage). Obviously by having the probe before the turbo it could cause an issue it something breaks off....

Post turbo some people are saying the EGT temperatures should be modifed to take into account the temperature drop across the turbo. For example (taken from another vehicle petrol/diesel ??) , a temperature drop across a 65% efficient turbine could show the following: 20psi boost, 20psi backpressure, Pre turbo EGT's of 750 deg C, Calculated post turbo temp is 565 deg C, that's a temp drop of 185 deg C. and ...20psi boost, 40psi backpressure, Preturbo EGT's of 700 deg C, Calculated post turbo EGT's of 411 deg C, that's a temp drop of 289 deg C

But the temperature reading post turbo will be more stable (which could be a good or bad thing).

So what are your thoughts..?
:-)

G

[97_gq_lwb]

I did a little research into it a while back and i will be fitting mine pre turbo.

[the evil twin]

A very, very complex field that essentialy is governed by what you "need" from the EGT indication. By that I mean for example turbine engines where 980 deg is eco cruise, 1020 is max cruise, 1032 is sprint and 1072 melts the engine so a matter of a few degrees affects speed, range and engine service life.

A turbine engine may have up to 32 probes in Inlet to get the absolute optimum reading it is so critical.

Sooo... what about a Patrol? Well, pre turbo will give the best indication of the combustion temps which is what makes or breaks the engine but is it that big a deal?

IE are you looking for temp limits or history to decide if the engine needs to be pulled down because it is being operated up near the raggedy edge and it went over the line for too long or too often before you melt a valve or whatever?

IMHO, for a reccy vehicle like a Patrol post turbo is fine. We err on the side of caution with the post turbo peak sustained EGT's anyway.

What nearly everyone is looking for is 1 of 2 things. Either an unusual drop/rise in sustained temps indicating something is wrong like a MAF fault or whatever... or... a normal operating range such as if the EGT is rapidly rising and looks like going north of say 500 degrees you back off or change gears to reduce load.

Bottom line, purely IMHO...
If you want to know the actual peak combustion temps then pre Turbo for sure.
If you just want to operate the engine below a level where the risk of damage from high combustion temps is dramatically increased, then post Turbo is fine as well as cheaper and easier.

[MudRunnerTD]

Yeah what he said ^^^^^^^

LOL

also for your interest mate, near everyone you will chat to online or stuff you read will be talking in Celsius temps and 98% of the time it will be a Post Turbo reading. For you to make real sense of all your research then you want to be able to compare what you read with what you see. Stick with Post Turbo for ease of assessment for sure.

I have run mine in a Pre Turbo position and to be honest found that the readings were so quick to spike up and change around that it did my head in. trying to convert a differential from a pre to post turbo reading will be enough for you to crap yourself or give up.

Stick with Post Turbo and stay on teh same page as everyone else. If your in doubt then you can bring your numbers to here or to your tuning Centre and we will be able to comment based on comparing with what we run in our own cars.

I Vote Post Turbo and have moved my Pyro to a Post Turbo position and am far happier there.

[97_gq_lwb]

Here i knew their was a good reason i fitted mine pre turbo.
Have a read
Mine reads quite well maybe others had poor placement or poor quality sensors.

[the evil twin]

Here i knew their was a good reason i fitted mine pre turbo.
Have a read
Mine reads quite well maybe others had poor placement or poor quality sensors.

... and the good reason is, what ? Careful, thats a trick question:smile:

Not being a smarty it's just that there is certainly a very valid reason for obtaining pre Turbo Exhaust Gas Temps and my next question is going be "OK, now you know the pre Turbo Temp, what is it allowed to be and for how long ?"

[97_gq_lwb]

From what i have read 700 is a safe level.
I did read somewhere that 2 minutes at 900 i think it was would do serious damage.
My reason would be that pre turbo gives you a more accurate temp where as post turbo can vary way too much to be accurate.

[robbo0001]

Won't these exhaust temps obviously depend on fuel type, engine size etc?
There may be a baseline that is able to be determined for each vehicle model, and I just try and watch what other peoples 2.8s are reading.

Our 2.8TD has never gone over 450 degrees celcius, even in soft sand, if I saw 700 or 900 I would whack it in neutral and stop bloody quick.
I whacked our pyro in, post turbo.

[the evil twin]

From what i have read 700 is a safe level.
I did read somewhere that 2 minutes at 900 i think it was would do serious damage.
My reason would be that pre turbo gives you a more accurate temp where as post turbo can vary way too much to be accurate.

Hmmmm... close enough for the discussion and great to see you are onto temps versus duration:smile:

But now for the next questions,
Why do you need the pre Turbo "accuracy".
Is 700 a safe level or is 720, 750 or even 800 OK?
Is a single Thermocouple sufficient pre Turbo and where does it need to be to avoid differing temperatures in the non laminar airflow?

Why those questions? Well, the whole purpose of the monitoring is to monitor cylinder head, valve and piston temps by interpolation from the Combustion chamber temps and EGT's. If the only advantage or reason for pre Turbo is accuracy then the only point to it is if you use the enhanced accuracy.

Basically unless the operator knows the temp limits and is using the data to run out near the raggedy edge of getting every ounce of performance before precipitate engine damage then post Turbo is fine.

Don't get me wrong. I'm not bagging pre Turbo. I am just saying that people using their Patrol in reccy applications don't need to stress about pre or post Turbo or the relevant accuracies.

Piston engine aero and most fixed plant ground installations are much more interested in Cylinder Head temps than EGT's as it is prolonged operation more so than brief transients that are an issue. That application of course sees fairly stable RPM and load however whereas vehicle engine loads and RPM's are constantly changing.

Bottom line... purely IMHO as an Instrumentation and Aero dude and not a Dieselly of course
if you run factory Turbo vehicles then EGT gauges are largely immaterial unless you cant drive for #$&$...
Start fooling with Chips, EGR, Exhausts, Fuel Pumps, Turbo settings or after market turbo's etc and...
if you want piece of mind and are happy potentially operating with a larger margin below peak performance then post Turbo is fine,
if you want to push the engine closer to the limits then the added expense (for the vast majority of people) of pre Turbo will be beneficial BUT you need to know those limits or it matters little.

Soooo... if you have the opportunity or ability to go pre Turbo do it but otherwise just (cough cough) go with the flow.:smile:

[YNOT]

I can see the relevance of pre turbo, as an example a TD42 fitted with a GT2860rs turbo. These are available with either a .86 or .64 exhaust housing. The .64 gives faster boost response but it's at the expense of higher EGT's. I don't know enough on the subject to comment accurately but I would expect the pre turbo temps to be similar with either housing, the higher EGT's being measured downstream of the turbine due to the concentration of hot gasses passing through the smaller .64 exhaust housing.
As has been said earlier, mixtures should be set using a mixture meter not a pyro gauge, the gauge should be used for monitering only, a bit like a coolant temperature gauge. Used that way pre or post turbo should come down to personal preference.

Tony

[97_gq_lwb]

I was contemplating a wideband but with the 1 fuel adjustment on the mechanical pump i can't really see the point.
That is unless someone can point one out.