EGT Temps Pre & Post Turbo

[Drager47]

Hey guys, I have a 1hdt 80 series with water to air intercooler and just had on the dyno and the fuel to air ratios good at 16psi but still getting high EGTs of around 650c and creeping up under load.
My EGT sensor is in the manifold pre turbo, the question I am asking is there much difference in temps pre and post turbo?

I know if you increase the boost and fuel more this also creates heat.

 

[Blown80]

Hi Drager, what was your AFR readings if you don't mind me asking. I imagine they're around 18-20:1.
Re the pre or post turbo temp readings, don't worry too much about what the difference might be in temps on either side. Lots of things can change that.
The important thing to monitor is the amount of change. As you noted, under load the change is clear under load and this is what you need to consider.
A post turbo reading at 300degC changing to 400degC under load is a significant change, over 30%.
Your pre-turbo reading at 650degC may seem high to everyone else's because they read post turbo, but if yours goes up to say 750degC is in fact a lesser increase at 15% despite being a higher number.
Just keep monitoring it and make notes so that if under normal or working conditions it changes more than usual then you can be aware of those moments and do something about it.

But those AFR readings from your dyno run will tell more about your EGTs and where they should or could be.
Cheers

 

[Olazz]

Yep there sure is... post Turbo temps can be +/- 150-200º. Should ideally be installed pre turbo. I had a similar problem after fitting aftermarket bumper and ancillaries to my 1hdt.

Simply moving the number plate letting more undisturbed air get in, dropped my EGT reading to below 520º from 600º+ , even under load.

 

[Drager47]

Hi Drager, what was your AFR readings if you don't mind me asking. I imagine they're around 18-20:1.
Re the pre or post turbo temp readings, don't worry too much about what the difference might be in temps on either side. Lots of things can change that.
The important thing to monitor is the amount of change. As you noted, under load the change is clear under load and this is what you need to consider.
A post turbo reading at 300degC changing to 400degC under load is a significant change, over 30%.
Your pre-turbo reading at 650degC may seem high to everyone else's because they read post turbo, but if yours goes up to say 750degC is in fact a lesser increase at 15% despite being a higher number.
Just keep monitoring it and make notes so that if under normal or working conditions it changes more than usual then you can be aware of those moments and do something about it.

But those AFR readings from your dyno run will tell more about your EGTs and where they should or could be.
Cheers

Hi Blown80,

Yes correct AFR are just under 20:1
When giving the lead foot gets up to 650 then creeps up just under 680c and holds. Even driving around 60km slight load around 550-600c. 100km around 450-550km touch the pedal and up she goes

Plus I have fitted Plazman WTA which has bigger radiator in the front with 12" fan which also restricts the air flow along with my trans cooler.

Thanks will monitor and load up with my boat next.

Cheers

 

[Blown80]

That doesn't sound all that bad. The temp readout is relative to where the pyro is located, on either side of the turbo, and being on the manifold side it will be a lot more reactive to changes. The turbo side not only soaks up and dissipates some of the heat before the pyro reads the exhaust gas temp, it means it is also a little slower reaction.
Ive seen some poorly designed dump pipes with the pyro port over 150mm from the turbo flange making the reading unreliable although rather cool.
With those AFRs I'd be comfortable with the rate of change and levels. If your coolant temp gauge is stable and the system is doing its job, then sounds all ok. EGTs will always fluctuate under load or off load, most people never see it so are oblivious to the effect on EGTs when dumping the foot on the throttle on a hill.

 

[pberrey]

Would adding more fuel without increasing the boot pressure reduce the EGT?


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[Blown80]

Adding more fuel, as in lowering the air:fuel ratio, or making it richer in simpler terms, will increase EGTs.
This effectively happens when you put your boot into it when slugging up a hill, the engine is struggling for revs therefore not getting the air in and its being loaded with more fuel.
That's why the EGTs sky-rocket on hills or pulling hard.
If you do the same intentionally by winding up the fuel load it will just run hotter all the time.
You may achieve more power, but only for so long......
Cheers

 

[pberrey]

When you are putting your foot down theres lots more air going in than fuel. Its not the fuel that is creating the heat, its the explosion of the oxygen. Leaner mix equals a hotter combustion chamber and vice versa has been my experience.

 

[adrianr]

Leaner mix equals a hotter combustion chamber and vice versa has been my experience.

In diesels it is the opposite isnt it?

 

[Towpack]

With diesels more fuel = more power and a lot more heat. Just watch a truck race and see the plumes of black smoke from the exhaust as evidence of the massive amounts of diesel being used in a quest for more power. Increasing boost, or forcing in more air, to match the increased fuelling will help bring down EGT's but the catch 22 is that compressing the air with more boost heats up the intake air so an efficient intercooler becomes a must. As has already been said a pre-turbo or manifold mounted pyro will be way more responsive due to the heat soak effect of the turbo when it's mounted downstream of it. Ideally you want the pyro as close to the head as possible as it's the cyl head/piston temp you have to control 'cos it can kill an engine. I have mine mounted in the manifold and the lag in temp change indication is virtually 0. If you want to start tweaking fuelling and/or boost an EGT gauge is an absolute MUST IMO.

 

[pberrey]

Up to a point i would agree.

Over-tweaking the fuel, if you want to think about it that way, will not give more heat because its not making any more power because boost has now become the limiting factor. It will reduce the amount of oxygen in the cylinder which seems to bring down the EGT for the same power/load conditions. Thats why some black smoke under load is generally a good thing.

I agree that an EGT gauge is essential and i wouldnt advocate people tuning without understanding their engine temperature. Whats important is understanding what is normal for your vehicle and the load conditions. If you tweak and say add an intercooler which brings your EGT back to pre-tweak levels it doesnt matter if you measure before or after the turbo for example. Its the increase that matters and you can then drive/tow to your EGT rather than water temperature.

 

[pberrey]

Power = heat
More fuel doesnt always equal more power therefore it doesnt automatically equate to more heat

 

[Towpack]

Up to a point i would agree.

Over-tweaking the fuel, if you want to think about it that way, will not give more heat because its not making any more power because boost has now become the limiting factor. It will reduce the amount of oxygen in the cylinder which seems to bring down the EGT for the same power/load conditions. Thats why some black smoke under load is generally a good thing.

.

Running at high altitude will also increase EGT's due to the DECREASE in oxygen in the burn. Doesn't really matter wether you increase the fuelling of decrease the air flow the effect will be the same. Tuning for more power at sea level or low altitude will certainly bring problems at higher elevations. Not really an issue in modern diesel engined vehicles full of sensors and with 'intelligent' electronic control of the fuelling and boost but on old mechanically fuelled diesels they have to be managed by your right foot. JMO

 

[Blown80]

Sorry pberrey but I have to disagree. We are talking diesels here. Old school diesels in fact.
Old Diesel engines don't even need a throttle body to control airflow, as fuel is what determines what is happening.
Reduce fuel and and what happens, you go down to idle. It doesn't get hotter at idle.
You can pump a Diesel engine with as much air as you like, but without fuel there is no heat created.
Add fuel and it burns, the more fuel and it burns longer so more power is produced increasing revs, and it runs hotter.
Keep increasing fuel beyond what can be efficiently burnt will simply increase cylinder head heat.
The fundamentals of diesels is pretty simple, but I can assure you that adding unnecessary fuel load, as in a rich mixture will increase heat.

 

[mrdelmonti]

I'm agreeing with Blown80 adding more and more fuel will end up with an inefficient burn with one of the results being increased heat, right up until you start washing the bores and filling the sump.

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[pberrey]

This is going off topic somewhat now (sorry OP) but engine speed would not vary the AFR. I'm talking about varying the fuel pump and boost settings to control EGT for the same engine speed and load. Not the absolute amount of fuel being consumed which obviously increases with engine sped and vice versa.


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[Nekros]

Blown80 is on the money! when I fitted up my turbo to my 2H I upped the fuel to get the power I thought I was after but all I did
Waas increase the amount of black smoke and send my EGT's through the roof! A mate helped me out by explaning what the go was and now
not so much smoke and Egt(after Turbo) max out at 500degC.