Megasquirt Support Forum (MSEXTRA)

I am looking into the egt option for megasquirt.

I am wondering what is the main reason to use egt’s.

Is it to monitor each cylinder temp to adjust fuel? Is using an wideband and using the trim table to do each cylinder more accurate and accomplishes the same thing? Or is there something else I am missing?


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My opinion? EGT is of little use in tuning for best power or fuel economy. It can help "balance" cylinders, especially if one is near-dead. EGT will show a non-firing cylinder quickly. EGT is also probably useful to avoid burning up exhaust parts when lots of boost is being used; not a concern for me with only NA engines.

It is useful to trim fuel as you say but it will not help you determine anything in terms of spark timing.

As Bill said it can be a useful diagnostics tool to find misfires.

I use it for limit monitoring during steady state calibration personally. Port temps on an NA or pre turbine temps on a turbo. It helps to determine when more fuel is needed to avoid components getting toasty so that I am not adding unnecessary fuel at any point.

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Never used one, but I thought that exhaust temps reacted to ignition timing. So as long as you have good baseline, you should be able to at least monitor burn efficiency differences between cylinders (assuming that the fuel is already balanced)

Yes it does. More ignition timing = lower EGT but that is always the case. As in EGT will not tell you if you are before or after MBT or when you run into knock so as a timing calibration tool it next to useless.

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And when you combine the analysing with data from individual ego's + knock sensor ?

Really good for balancing out fuel (need to know which side of stoich you are on) and knowing when/where/how a cyl goes down.

But wouldn’t you prefer using individual o2 sensors for balancing out the cylinders?

Motoren wrote:But wouldn’t you prefer using individual o2 sensors for balancing out the cylinders?

Yes. But it's usually more expensive and the sensors are sensitive to heat and pressure.

Jean

racingmini_mtl wrote:

Motoren wrote:But wouldn’t you prefer using individual o2 sensors for balancing out the cylinders?

Yes. But it's usually more expensive and the sensors are sensitive to heat and pressure.

Jean

That's not a big issue, at least on mine it isn't.

Yves wrote:

racingmini_mtl wrote:

Motoren wrote:But wouldn’t you prefer using individual o2 sensors for balancing out the cylinders?

Yes. But it's usually more expensive and the sensors are sensitive to heat and pressure.

Jean

That's not a big issue, at least on mine it isn't.

I assume you don't have a turbo engine. That's where it can become quite a bit more complicated. On a N/A engine, that's more straightforward.

Jean

N/A indeed

Yves wrote:And when you combine the analysing with data from individual ego's + knock sensor ?

Then you make it simply a limit monitoring sensor.

And contrary to some other comments you don't need to know what side of stoichiometric you are. If you add fuel and egt rises then you are lean of stoichiometric, if you remove fuel and egt rises then you are rich of stoichiometric.

In my opinion EGT is a far more cost effective and space saving method of doing the same job as individual EGOs.

Edit: got my rich/lean backwards

motthomas wrote:

Yves wrote:And when you combine the analysing with data from individual ego's + knock sensor ?

Then you make it simply a limit monitoring sensor.

And contrary to some other comments you don't need to know what side of stoichiometric you are. If you add fuel and egt rises then you are rich of stoichiometric, if you remove fuel and egt rises then you are lean of stoichiometric.

I think you got that backwards.

motthomas wrote:In my opinion EGT is a far more cost effective and space saving method of doing the same job as individual EGOs.

EGT is not only dependent on fueling but on other factors such as ignition timing and cam timing (among others). So you don't know from EGT alone how much fueling needs to be adjusted. Moreover, you cannot have the ECU autonomously perform fuel correction for individual cylinders from EGT but you can from EGO (on the MS3).

Jean

racingmini_mtl wrote:

Motoren wrote:But wouldn’t you prefer using individual o2 sensors for balancing out the cylinders?

Yes. But it's usually more expensive and the sensors are sensitive to heat and pressure.

Jean

But you can do individual Cylinder trim with one spare O2 sensor. Takes some times through.

And you probably will remove the O2 sensors when done tuning or they won’t last very long time so close to the exhaus port

Yes I did get it backwards. It was late! Corrected in my original post now.

Yes you are right that the ECU can't do closed loop fuel control on EGT so that is going to be the main reason to go for individual EGO. However the cost difference is so large that I would struggle to justify the cost-benefit of EGO. I mean you can build a 4 cylinder EGT setup for under £100 while 4 EGO sensors and controller could run close to £500. And thats if you can afford to fit 4 M18 bosses and sizeable sensors in your engine bay. That sort of cash saving can buy a lot of other mods for a project. If you go into 6 or 8 cylinders then the cost of individual EGO sensors quickly becomes massive overkill for a relatively small time saving during calibration.

Yes you are also correct that EGT depends on a lot of factors but for fuel trim you can ignore all that. We aren't looking at the absolute temperature values (unless limit monitoring) but rather the temperature differential between cylinders. Once appropriate trims have been applied for a given speed and load point, the trims won't need to be changed unless injectors or gas path is changed so having closed loop trims seems overkill to me.

No EGT differential won't give you a steer for how much trim is needed so it is a more time intensive and trial and error based approach but if you are using a steady state dyno to set up your fuel & spark tables then this is the perfect chance to dial in cylinder fuel trims.

It's an individual choice at the end of the day and my preference for EGT is based on my own opinions and values. I just find it very difficult to justify the most of the cost of an ECU for very little benefit.

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But you can still do the job with one extra O2 sensor throught. I haven’t tried the individual cylinder trim with only one O2s sensor through.

Motoren wrote:But you can still do the job with one extra O2 sensor throught. I haven’t tried the individual cylinder trim with only one O2s sensor through.

Horses for courses lad. It can be done that way but in my opinion you are creating a lot more work than necessary by constantly swapping a sensor between cylinders for not much if any cost saving over an EGT system.

I am also not a fan of introducing flow disturbances in the primary headers from the lambda bosses / bungs. Each to their own at the end of the day.

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just for info purposes, I am not telling you what to do or not do. my experience with egt, is that is a good reference on boosted or nitrous combos. this is only on the dyno also. afr is way more reliable. I generally will put egt on the "hottest hole" and just monitor. AFR is your friend.

I think measuring EGT (i.e. comparing) would be really useful on my V8 where I know the airflow is, due to the design of the intake, slightly unequal to the cylinders. It would give me a chance to balance the individual cylinders. Will be next addition to the system...