EGT Gauge - Pre or Post Turbo?

[SimonW]

I am having a turbo fitted to the 1HZ motor in my Troopy.

Do EGT gauge sensors normally go pre or post turbo?

And when I see recommendations that the EGT on a turbo 1HZ shouldn't go above about 550 degrees celcius, is that pre or post turbo?

Thanks.

[Shonky]

Typically most go with post turbo just cause it's easier to fit the probe. I fitted my one pre-turbo which was a bit more work, but it does remove the variation in temps that you can get mounting the probe post turbo due to the turbo itself soaking some heat out of the exhaust gas. If you can get the probe fitted to the exhaust manifold before the turbo is fitted it will make life easier in regards to fitting.

From what I've read from a lot of sources, 550° is the max you would want to see post turbo. Take a look at this article on EGTs, it quotes figures in °F so you will have to convert to °C.

In that article, it quotes (870°F) 465°C when measuring in the dump pipe due to maximum temp difference that can be seen between pre-turbo temps and post turbo. Make of it what you will.

[DJR96]

Pre-turbo is more accurate and responsive. Pre turbo you can use actual temps. Post turbo you have to make an "allowance" for turbo heat soak, which is a bit of a grey area.
If you can arrange to get it installed as part of the turbo install, it shouldn't be too hard at all. Maximum temp could be up to 675 degrees Celsius (1250 f).

[SimonW]

Thanks for the replies.

Unfortunately, by the time I asked about pre/post turbo for the EGT gauge, they had already installed the turbo and exhaust, and have dynoed and tuned the system.

They are not very keen to put it pre-turbo now, and have commented that they normally go post-turbo, and that there is a position on the kit for it to be mounted post-turbo.

So it looks like I just have to live with it being post-turbo, and maybe find out if I can have it mounted pre-turbo when I have an intercooler installed later on.

It sounds from what I have read that I should keep it below a maximum of 465-550 degrees celcius (depending on what I read, or who I listen to) on the post-turbo EGT gauge.

Thanks for the info and advice though.

[me3@neuralfibre]

Go Pre

Post doesn't tell you much useful that you couldn't guess at anyway.

Paul’s esoteric meanderings » Blog Archive » Fitting a Diesel EGT and Boost Gauge

Paul

[Peter @ Aawen4x4]

A fair portion of the heavy transport fleet running diesel engines have been running post turbo EGT sensors for a long time now, and the information that can be derived from those post turbo temps is pretty reliable! It is for that reason that most Turbo kits you can purchase already have mount points for the EGT Probe in the exhaust dump pipe - it's where many of the big trucks have them, and lots of the turbo gear we use on our 4by's is either borrowed direct, or scaled down from those pieces of kit!

So don't worry too much about your temp probe being post turbo, the diesel fitter/tuner types out there that may get to see your vehicle for diagnosis, tuning, or repair will be able to tell you what's going on with your diesel engine just so long as they can get to see those temps and they know where they are coming from! It's really not a biggie!!

Cheers!

PS, 550 degrees C is pretty much the highest temp you'd want to let things get too with a Post Turbo EGT sensor!

[HDJ105]

Originally Posted by Peter @ Aawen4x4

PS, 550 degrees C is pretty much the highest temp you'd want to let things get too with a Post Turbo EGT sensor!

On my vehicle, 550C post turbo = ~700C pre turbo, which most would consider above the limit.

[Peter @ Aawen4x4]

That's why it pays to read this article first, Articles | Watching your EGTs (HiFlo Fuel Injection) before deciding on what YOU are going to use as your highest allowable level! That particular article suggests using 465 degrees C, but that's allowing for a possible 400 degree Farenheit difference between pre and post turbo temps. Before that tho', they highlight the fairly significant risks associated with pre-turbo mounting vs the range of variances possible in post turbo mounting! They then go on to highlight that the MOST IMPORTANT part of EGT's is actually MONITORING them!

I know people who won't go over 500 on a pre-turbo EGT, and others who feel happy to use 650 as the high level on a post turbo EGT set up! It's a choice that YOU get to make, balancing the risks against your needs!??

Personally, I think 500 is pretty much the limit for my TD4.2 with a post turbo EGT set-up, and that ties in with the temp measurements the turbo guys did when they were tuning it all up, so I'm happy! When they were setting it up, they suggested that 600 C was OK, but only for short periods, but they couldn't/wouldn't define SHORT any better than just that! So I'll stick to 500 and know that a bit over on the odd occasion probly won't cause any damage! What do you use as a max for your set-up HDJ?? Your EGT probe is pre-turbo isn't it?

[HDJ105]

Originally Posted by Peter @ Aawen4x4

What do you use as a max for your set-up HDJ?? Your EGT probe is pre-turbo isn't it?

Peter,

Not arguing, just pointing out (as I have done before) that people need to make their own decision, because the probe location plays a huge part in what it reads. There's no blanket ruling (as per trucking industry where there are less variables).

I have both pre and post probes (as this argument came up a few years back on another forum) and from personal experience 150C is the largest differential I've witnessed. I'd start to get cautious pushing over 650C for any period of time.

[Peter @ Aawen4x4]

Originally Posted by HDJ105

Peter,

Not arguing(??), just pointing out (as I have done before) that people need to make their own decision, because the probe location plays a huge part in what it reads. There's no blanket ruling (as per trucking industry where there are less variables).

I have both pre and post probes (as this argument came up a few years back on another forum) and from personal experience 150C is the largest differential I've witnessed. I'd start to get cautious pushing over 650C for any period of time.

Is that pre or post Turbo?

[DJR96]

650C post turbo would be a meltdown!

650C pre turbo is getting up near the limit of how hot a turbo can cope with without harm. To the point where you should be asking the manufacturer what the limit really is for that model turbo. Note too that any temp. up to the limit is ok, just don't go over it! Factor in a safety margin you feel comfortable with.

[Tomax]

I had one fitted post-turbo on my previous 105 Cruiser and the bloke who set it up recommended a max of 500 C , especially if the vehicle was to be doing some hard kms, which mine was. He set mine up with a max EGT of 475 C - no problems during 220000km

[me3@neuralfibre]

Originally Posted by DJR96

650C post turbo would be a meltdown!

650C pre turbo is getting up near the limit of how hot a turbo can cope with without harm. To the point where you should be asking the manufacturer what the limit really is for that model turbo. Note too that any temp. up to the limit is ok, just don't go over it! Factor in a safety margin you feel comfortable with.

EGT gauge is there to protect the engine, not the turbo. The turbo will cope with EGT's WELL over 800C, and up to 1000C for short bursts. This happens in petrol engines with too much fuel and short strokes. The turbo si basically the same except for trim and tuning.

A 700C EGT is the decompressed and de-energised gas from your engine. At peak combustion temp it was WELL above that, prob close to 1800C, as it has decompressed by a factor of 18:1. I'd have to go back to my thermodynamics books to work that out, far far too long ago, and I didn't pay enough attention then anyway. Luckily the 4 strokes, oil and water jacket keeps your piston / walls / head cooled enough to cope (it's only a 25% duty cycle). This is why jet engines can't handle gas temps 4 strokes can - 100% duty cycle, and why they circulate air inside the hollow turbine blades of modern gas turbines.

So, as the things that will cop the biggest flogging are anything alloy (lower temp tolerance) and anything pointy. Pointy would be valves, esp exhaust, injector tip, glo plug, and edges of pre-comp holes if you have them. Normally the heat is conducted away from these points, but if you add it faster than it can be conducted away... That's why there is a "short burst" theory, as they can soak up some heat for a few seconds before they melt. Now as they melt they may start throwing molten metal out the exhaust, and your turbo may have a bad day. That said, I melted a petrol engine with detonation with holes I could put my thumb through in 2 pistons, and the turbo was fine. They are pretty tough, depends on how big and if it sticks.

So it is hard to put an exact limit on it, as it depends on engine materials and combustion chamber flows. Indirect injection would prob be less tolerant than direct injection. I work off 720C being my safe max, and prefer to stay under 650 during overtaking etc.

Paul

[HDJ105]

Originally Posted by Peter @ Aawen4x4

Is that pre or post Turbo?

PRE PRE PRE PRE (the only accurate form of measurement)

[HDJ105]

Originally Posted by DJR96

650C post turbo would be a meltdown!

650C pre turbo is getting up near the limit of how hot a turbo can cope with without harm. To the point where you should be asking the manufacturer what the limit really is for that model turbo. Note too that any temp. up to the limit is ok, just don't go over it! Factor in a safety margin you feel comfortable with.

Not necessarily, very engine make / model specific, but it will definately affect longevity IMO.

A mates TD 100 series will easily see 800C after ~2mins of WOT, and it's still going ;-)

You will never get a 4WD vehicle manufacturer to specifiy a temp. limit in my experience.

[HDJ105]

Originally Posted by Tomax

I had one fitted post-turbo on my previous 105 Cruiser and the bloke who set it up recommended a max of 500 C , especially if the vehicle was to be doing some hard kms, which mine was. He set mine up with a max EGT of 475 C - no problems during 220000km

The HZJ105 is a special case, where EGT's are very important. And yes when installing an aftermarket turbo, intended use should also be a factor in how the tuner sets up the tune.

[DJR96]

Here's an article that may be of interest:-

Engine protection units - Exhaust gas temperature gauges

Surprisingly hard to find better info, even on the Honeywell/Garrett website.......... Will keep looking.

[Courts InSession]

The race boys will have a probe pre turbo in each runner, this is where EGT is extremely handy. That said its alot easier to wack it in post turbo and it will still give you a good guide if theres a problem.