Best way to use egt?

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Dennis_Zx7r
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Re: Best way to use egt?

Post by Dennis_Zx7r »

Just FYI, here's an exhaust system previously run in a high level racing series for a NA engine with over 200hp/liter.
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As you can see, this team used one EGT for each cylinder, and only 2 EGO sensors for cylinder 3 and 4 each (in-line 4 cylinder, cylinders in the middle run a little different than the outer cylinders). I however don't know why they did it this way, but I think it is highly unlikely that money was the reason.
For me however money does matter (4 Thermocouples +amplifier = 60€) and the EGT setup is a lot lighter, and that's why I started copying this setup as it seemed good enough. I'll have some data related to this in March or April at the earliest though.
My project: Link
motthomas
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Re: Best way to use egt?

Post by motthomas »

Yves, If you have seen the advantage of EGOs over EGTs and that advantage was big enough to justify spending the money on a multi-EGO system then that is the argument that is needed. Its just that up until now you have just categorically stated that EGO is great and EGT is useless without explaining why you feel this way or quantifying the benefit of one vs the other. EDIT: I am still interested in what sort of differences you saw between both methods that swung you towards the EGO system.

I am not trying to say that EGT is the only way to do things or to convince you that it is the best way. EGO works well, of course it does. But there is a big disadvantage in the cost of the instrumentation and so I feel that people shouldn't feel pushed towards that route just because it is someones opinion that the alternative is not worth considering. Personally, the cost vs benefit of the EGO system means I cannot justify it. I would rather put the money into a more powerful ECU. Obviously for some people this isn't the case and that decision is up to them.

I was not referring to calibrating the sensors in my point but rather calibrating the fuel trims. Tuning in other words. Also, OEMs use expensive sensors mainly to get each cylinder in the correct lambda range for best emission. Not necessarily for best power which is the goal of the majority of people that use a programmable aftermarket ECU.
Paul_VR6
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Re: Best way to use egt?

Post by Paul_VR6 »

Jean, my statement was across the board. I totally get that you *can* do individual cylinder ego it's just not the most practical thing in most cases. An engine dyno in a very controlled environment on a na setup is about as good as it gets.

I personally run 2 ntk widebands and 6 open element egt on my personal car. I could run widebands (its only money!) but not worth the hassle from all the other setups I have tried.
-Paul
1992 Corrado SLC 3.6 VR6 11.38@120 - MS3 Pro Ultimate - Microsquirt I/O - Can EGT - Racepak IQ3s
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Yves
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Re: Best way to use egt?

Post by Yves »

motthomas wrote:Yves, If you have seen the advantage of EGOs over EGTs and that advantage was big enough to justify spending the money on a multi-EGO system then that is the argument that is needed. Its just that up until now you have just categorically stated that EGO is great and EGT is useless without explaining why you feel this way or quantifying the benefit of one vs the other. EDIT: I am still interested in what sort of differences you saw between both methods that swung you towards the EGO system.

I am not trying to say that EGT is the only way to do things or to convince you that it is the best way. EGO works well, of course it does. But there is a big disadvantage in the cost of the instrumentation and so I feel that people shouldn't feel pushed towards that route just because it is someones opinion that the alternative is not worth considering. Personally, the cost vs benefit of the EGO system means I cannot justify it. I would rather put the money into a more powerful ECU. Obviously for some people this isn't the case and that decision is up to them.

I was not referring to calibrating the sensors in my point but rather calibrating the fuel trims. Tuning in other words. Also, OEMs use expensive sensors mainly to get each cylinder in the correct lambda range for best emission. Not necessarily for best power which is the goal of the majority of people that use a programmable aftermarket ECU.
The ego has a linear output in voltage vs the O2 content of the exhaust gasses. So you know when you are lean and when you are rich. With an egt, exhaust temps go up when richer and go up again when lean.
With an EGT you never know on which side of the curve you are, unless you go back and forth. If you tune that way, you set the VE in the table based on what you checked while tuning. Equally you can never do a closed loop fuel control with EGT's because the computer will never know which side it is on, the rich side or the lean side. With an EGO you will always know because the output of the sensor is linear.

In view of the fact that an egt allows you to measure temps you could however see the effect of ignition trim. I mean, retard timing for that cyl and more fuel will burn in the exhaust and temps go up, while the AFR should stay the same. The other way around when you advance timing, more fuel is burned inside the cylinder and with the same AFR you should have lower exhaust gas temperature (more converted to work at the crank). So assuming you have a well tuned table and every parameter that affects it under control, you could basically trim individual ignition timing requirements to get the same amount of fuel burned in the cylinder and thus the same exhaust temperatures to perfectly balance your engine.
The caveat however is that in my experience the fuel curve of each cyl will always need trimming when driving and it differs from one situation to the other. In a dyno room where everything is controlled, tuning the ignition trims might be possible. However you will never know if this will still be correct once you hit the road.

What my thinking was, is that you first need to get your fuel set right and then look at the temps of the exhaust and balance those with ignition trim. But this is a costly thing as you would be running both ego's and egt's. Once set you would have no more need for egt's as there is no closed loop control. In practise I doubt it will be possible for the above mentioned reason.

I'm not sure as to using individual wb's on a turbo setup with which I have no experience. You cannot place them too close to the exhaust port, which might make it impractical as you would want the turbo close to the head. This might place the WB's in a temperature range that might exceed the specs. Like said, there are several things that could be done like a long bung, cooling fins. etc. Of course this complicates things as well.
Personally and if room allows I would make the primaries before the turbo longer so you have the wb's at a suitable range after the port so they are still useable. It might prevent a lean cylinder and in the end a melted piston. Like with everything trade offs have to be made here.

As a safety device, to make sure your exhaust doesn't run up too high, I can see uses for egt's. However I do not run a turbo, so I'm not in the range this poses a risk for my combo.

PS : the WB that is closest to the port on my V8 is the number 4 cyl and it's at about 15-18 cm from the port.
Paul_VR6
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Re: Best way to use egt?

Post by Paul_VR6 »

You are confused with how afr effects egt. It is peak at stoich and drops on both sides. Its pretty simple.
-Paul
1992 Corrado SLC 3.6 VR6 11.38@120 - MS3 Pro Ultimate - Microsquirt I/O - Can EGT - Racepak IQ3s
kptuned.com - Megasquirting the World! Megasquirt Sales, Service, Tuning and More!
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Yves
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Re: Best way to use egt?

Post by Yves »

Paul_VR6 wrote:You are confused with how afr effects egt. It is peak at stoich and drops on both sides. Its pretty simple.
My point being that egt's are not linear and thus not suited for tuning fuel especially in closed loop. It's been too long since I looked at them.

Anyway, retarding ignition = hotter exhaust, advancing ignition = less exhaust temperature (up to a point). We are talking about comparing relative exhaust temperatures when a change is made, not absolutes in terms of temperatures affected by ignition trim.
Effect of fuel ratio vs effect of ignition timing on exhaust temperatures, two different things but one effects the other obviously. A richer mixture needs less timing thus overal lower exhaust temps, leaner mixtures and you have overal higher exhaust temps. Advance ignition on a richt mixture and overal exhaust temps drop while still being non-linear, retard it and overal exhaust temps go up, albeit non-linear.
So albeit you can see an effect of ignition on overal/average exhaust temps, you cannot see whether you are on the rich or the lean side of the fuel ratio. You have to go back and forth by richening up, leaning up to see where you are.

As for me I don't see the use of them as even with a good tune, you will see the engine not running perfectly on the AFR you set it at. Other factors influence things, so you need something to make the minute fuel corrections. The egt's to trim ignition at that point are only good for icing the cake so to say.
This is specifically the case for a long duration, high overlap cam, where the fuel ratio swings tend to be big.

Cost factors and installation issues aside (close to the port) I don't see a lot of reasons for egt's, but again that's my personal opinion on things.
Paul_VR6
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Re: Best way to use egt?

Post by Paul_VR6 »

You can easily see what side of stoich you are on by adding fuel and watching egt. Millions of engines have been tuned this way long before any exhaust ratio sensors were used.

Egt alone isn't optimal, and it is much easier when combined with a wideband or two.

If your ve cylinder to cylinder is considerably off, I would suggest building better engines. If rules prohibit that, there isn't much else to be done than what you can with what you have.

If you are taking street cars or mild use this is all just a paper exercise anyway.
-Paul
1992 Corrado SLC 3.6 VR6 11.38@120 - MS3 Pro Ultimate - Microsquirt I/O - Can EGT - Racepak IQ3s
kptuned.com - Megasquirting the World! Megasquirt Sales, Service, Tuning and More!
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Yves
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Re: Best way to use egt?

Post by Yves »

Paul_VR6 wrote:You can easily see what side of stoich you are on by adding fuel and watching egt. Millions of engines have been tuned this way long before any exhaust ratio sensors were used.

Egt alone isn't optimal, and it is much easier when combined with a wideband or two.

If your ve cylinder to cylinder is considerably off, I would suggest building better engines. If rules prohibit that, there isn't much else to be done than what you can with what you have.

If you are taking street cars or mild use this is all just a paper exercise anyway.
When was the last time you looked at individual VE's of different cylinders of an engine, any engine ? Especially one that has a cam worth that name in it ?
Paul_VR6
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Re: Best way to use egt?

Post by Paul_VR6 »

Quite a bit actually. The engine I specialize building is a complete mess in that regard and most of it is fixable. What isn't is easily tunable once you understand things. Even without all cyl ego.
-Paul
1992 Corrado SLC 3.6 VR6 11.38@120 - MS3 Pro Ultimate - Microsquirt I/O - Can EGT - Racepak IQ3s
kptuned.com - Megasquirting the World! Megasquirt Sales, Service, Tuning and More!
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