mattski2

Just wondering what a safe limit for Exhaust Gas Temp is?
My car normally sits around 600 degrees C on motorways but
I gave it some stick earlier (110mph on a private road ;-) )
and EGT rose to ~700 degrees. I understand that EGT can be
as good as a lambda meter for knowing if the car is leaning
out (i.e. hotter temps) but what is 'safe'?

ta,
Matt

JIM THEO

It is depending from the place you fitted your EGT probe...

mattski2

ahh, ok - EGT probe is just after the turbo on the downpipe (goes in from the top, prob about level with the other sensor)

Hoppy

Matt, interesting question. Obviously, where you position the EGT sensor has a big effect on readings (no point in putting it in the back-box, then ). But the real question is what do the relatively different readings mean?

So EGTs rise. I think high temps can sometimes be an indicator of efficient combustion. Other times they are a warning of lean running, detonation, or potential detonation. Which is very bad.

What does EGT tell us? And if it's the danger of det, aren't inlet temps a better, and earlier, warning? Or a knock (det) sensor?

Cheers,

Richard.

BugEyed

Matt

EGT's of 850 C measured near to the head are about the limit for a reliable engine (I've happily run 1000+ on race engines, but they are a bit different). You will be under-reading by about 100-150 C due to the distance between the head and your probe, so you are close to the limit.

In terms of tuning, an EGT is not as useful as a wide band O2 sensor as it isn't as sensitive. Having said that, it will report major problems (particularly fuel pump/injector related) and is a good safety device. A number of people (including some respected ECU tuning people) seem to think they can tune on a narrow band O2 sensor which means they are running at a big risk.

Duncan

mattski2

thanks for the replies guys - v.useful.

re: being near the limit, what can I do about it as I would assume that EGT will rise when going above 110mph (arguably not a worry due to the speed but even so...).

Would lowering charge temps make any difference? (have an HKS FMIC on the way but was thinking of selling it, if it's a safeguard for the engine + performance gain I may think twice).

Would another ECU solve it? (maybe EcuTek or Link, Motec etc)

Or... what about somethink like an HKS AFR to richen the mixture a bit, alternatively would something like ERL water injection make things better?

I guess I could be worrying about nothing, the car is running fine and made good power @ PE (270bhp @ 6100rpm + 254lbs/ft of torque @ ~2900rpm) but I would like to make it safe power rather than power for the sake of it.

oh, the car has a scoobysport downpipe, HKS Hiper mid + rear + HKS Racing Suction kit and PPP ECU.

ta,
Matt

john banks

My EGT is in the headers and reads up to 740 C presently with big exhaust, intercooler, hybrid TD04 at 20 PSI. The highest I got was 760 with the original intercooler and small exhaust.

Unless you are running lean for some reason (I would be surprised unless there is a MAF fault or misread) then I am surprised how high your numbers are.

After the downpipe is a "bad place" for an EGT probe since it gets all the heatsoak effect from the turbo, numbing response and dropping the EGT by a variable amount depending on circumstances. The reason for knowing EGT is to estimate in-cylinder temperatures and make sure you aren't turning the turbo into a danish pastry.

Arguably WI has no place as a band aid for bad fuelling (Corky Bell) but it does not seem to harm others although Andy F would tell you his fuelling is not "bad" just "appropriate"

Andy.F

Agree with the comments above. EGT's will continue to increase as you approach the stoichiometric mixture. Mixtures either side of stoich will result in lower EGT's, this is due to incomlete burning due to excess fuel or air.
Our engines generally run way up on the rich side of stioch As we weaken the mix, the EGT increases, indicating increased efficiency As Duncan states, if the engine materials could withstand the temperatures then a weaker mixture would produce more power.

I would suggest you relocate your EGT gauge to a point in the headers in order that it gives a representative output.

Oh, your FMIC, whilst great for power etc, is likely to supply even more air for combustion !

Andy

mattski2

hmm - well, I had a new MAF sensor on saturday, Chris @ PE discovered it was running lean on the road but it should be fine now, he changed it and it was 'fixed'.

Do you think it could be the HKS Racing Suction kit causing it to lean-out?

Any ideas re: fixes?

M

mattski2

ok... so I need to get more fuel in then?

also - if I move the EGT sensor to the headers what can I do about the resulting hole in the downpipe?!

ta,
Matt.

EvilBevel

Duncan, could you elaborate a little on this ? I do realize that a standard O2 sensor will quickly underread as the EGT's rise, but that would make those tuners err on the rich side of things wouldn't it ?

Perhaps I'm asking: what is it you see with a wide band that you can never catch with a normal O2 sensor ?

Andy.F

Matt - Depends on the interpretation of 'lean' Most tuners call anything that isn't stinking rich 'lean'

R19KET

"In terms of tuning, an EGT is not as useful as a wide band O2 sensor as it isn't as sensitive. Having said that, it will report major problems (particularly fuel pump/injector related) and is a good safety device. A number of people (including some respected ECU tuning people) seem to think they can tune on a narrow band O2 sensor which means they are running at a big risk."

I really don't agree with this. A lot of race teams will tune, purely based on EGT. EGT's tell you if you're running rich/lean, and also what's happening with cylinder temps.

I agree that a wide band is better than a narrow band lambda sensor, but if you know what you're doing, and understand the drawbacks of a narrow band, they are fine for the level of tune most people need.

Just because your AFR's are ok, doesn't mean that your EGT's are.

If I had to make a choice, I'd choose EGT, and AIT, over AFR, any day.

Mark.

john banks

I curse the things Theo every time I do a car. You have to take them with other information and wonder about the precious MAF sensor and fuel pressure as well. It is fine when an unmolested car arrives with a 930 mV lambda reading (?15% CO don't have a table that goes that high and it would be inaccurate anyway) and I send it away at 890 mV. But when a car arrives and when the sensor is not overheated and the values are 860 mV I just weep because I know it is going to be a nightmare working out which sensor is telling the truth and which is not! The new cars might be quite a lot better.

RICH WILD

I have my EGT probe in the manifold and the highest I have seen is 900 degrees, but by this time you are at silly speeds, in normal blasting around town, the gauge hardly gets past 600.

Prolonged high speeds seem to be what realy gets the EGT "up there" as you are permanently on boost in 5th gear.

I'm looking at beefing up the fuelling to try and bring these temps down. Was looking at an FMIC too but as Andy says, I presumed that this would make things even leaner!!

Cheers

Rich

mattski2

bl00dy car :-\

so I need to get more fuel into it then guys? how?!
considering it has had a new MAF sensor is it just that
it (with the mods) is on the limit of what the PPP ECU
can manage?

M

Andy.F

New uprated fuel pump is your best bet. Even on the standard regulator you will hold more fuel pressure at max power with the uprated pump. Idle annd cruise will be unchanged.

BugEyed

EGT's are useful, but they are not as sensitive to the ideal AFR as a good wide band sensor. Their main use is in picking up problems and in preventing running excessively hot. For race engines you nearly always run into temperature problems and have to run away from the ideal AFR to keep it cool.

A narrow band O2 sensor is only good for tuning around the stoichimetrically correct point. Often you want to tune at different points, hence the need for wide band. Being a cheapskate with an MY01, I use the standard wide band for two reasons - accuracy and the fact that it is nearer to the engine than the narrow band. I don't subscribe to the "alleged" problems of the narrow band with temperatures - yes it loses accuracy but you wouldn't be using it if you wanted absolute accuracy!
Agreed. Check both, or you may live to regret it.
Or all three!

Duncan

R19KET

Duncan,

What your graph shows, is that a narrow band isn't very good below 14.7:1, but does work in the on boost areas. Obviously the granularity of a wide band is better.

The graph also shows that the narrow band "shows" leaner, as the temps go up.

I think you'll find that this is common knowledge amongst tuners, or it should be.

Now, since the Jecs uses a narrow band to control the fuelling on all pre '01 cars, and most car manufactures use narrow band, I think it is a little misleading to suggest that tuning with a narrow band is asking for trouble.

I agree that a wide band is better, but since most people are going to use the stock sensor, regardless of what is used to tune the ecu, it's pretty pointless.

There are VERY few ECU's that can use a wide band. Even Motec use a "wide range", based on 0~1v, and then they charge £500 for the software (iirc).

I do use a wide band, but then I have a Pectel, and the sensor alone costs circa £350 + vat !!!

The most important thing, is that the tuner knows what he is doing. I'd rather trust a GOOD tuner, using a narrow band sensor, than a cowboy tuner, making out he knows what he's doing, just because he's got what's probably a "wide range" set up !!!

Mark.

BugEyed

Most manufacturers use a narrow band in "closed loop" mode to keep at or around a stoiciometrically correct ratio. I agree that it is adequate for this purpose. But, in "open loop" mode most ignore the sensor. For tuning to create an "open loop" map, manufacturers have been using wide band sensors for 20+ years. Whilst most of these were/are too expensive for everyday use, to a large scale manufacturer the cost during development was/is not an issue. It only becomes an issue for "small scale" tuners.
Not if you have an MY01+ that has something approaching a wide band as stock in a better position than its narrow band.
Ouch. The MY01+ "wide band" sensor is reputed to be about £240 + vat, so I hope I don't chew mine up.
Agreed. It's not what you've got, it's what you do with it (or so my Wife says ). How often on this board do we read about people who have had problems with cowboys caliming more ability than they have.

So in conclusion, both of us will continue to use our wide band (not truely in my case, but a lot more than a narrow band) whilst a number of people will continue with their narrow band. Each to their own.

Duncan

PS Sorry about hijacking the thread!

mattski2

right ! all interesting stuff and a great thread (if a bit over my head !) but what should I do and who should I get to do it?

ta,
Matt.

john banks

I am happy with my narrowband reading 880-890 mV on boost on the first drag after cruise conditions with the EGT peaking at 720-760 absolute max. You just have to leave a margin (which we are anyway) and know the limitations. All sensors are the same in that respect. Thankfully this sensor is pessimistic.

BugEyed

Matt

Take the earlier suggestion about relocating the EGT from the downpipe (Scoobysport can sell you a bung as can any decent engineering supplier) into the headers - there is a nice spot by No3 where there is a boss on the manifold that you can drill and tap to fit an adaptor.

Secondly, take your car to somebody you trust to check the fueling on full chat (a reputable rolling road or mapper can do this for you). It may be that you could replace your current PPP ECU and get a custom map to give your more power with a decent safety margin. Whilst the PPP map is far better than standard, it will not have optomised the ignition or the fueling for your set up with its improved breathing.

Thirdly, the FMIC will allow you to flow even more air than you already are. Don't fit this unless you are willing to do the first two steps. If you want a re-map, don't get that done until after fitting the FMIC if you intend doing so at a later date.

Hope that helps.

Duncan

PS AndyF (aka Cossie Convert) - I'm not sure I understand your comment about excess fuel causing high EGTs. In my experience you can cool high EGTs by adding extra fuel at the expense of power and emmissions - in fact I think this is what Subaru have done on their map as it runs hugely rich.

Edited to add - Matt, on reflection I think you might be correct to be worried about the temps. Have you had your fuel pressure checked recently? I'd be suprised if you are running out of pressure, but maybe you've got a problem with the regulator or a blocked fuel filter.

[Edited by BugEyed - 6/13/2002 4:08:58 PM]

Andy.F

""PS AndyF (aka Cossie Convert) - I'm not sure I understand your comment about excess fuel causing high EGTs. In my experience you can cool high EGTs by adding extra fuel at the expense of power and emmissions - in fact I think this is what Subaru have done on their map as it runs hugely rich. ""

Duncan

I don't think I said that

Andy

BugEyed

Andy

You're right - you didn't say that! Apologies for the slurr - I'd better learn to read more carefully. Having re-read it I agree with what you said - and anyway your observation is no doubt based on your experience.

Duncan

Andy.F

No problem Duncan

Do you know if these standard narrow band sensors will read more accurately at high temp if the heater is switched off ? Or does the heater get switched off anyway by the ECU ??

Andy