Tuning with a EGT

[rcchong]

hi all sifu
has anyone here have experince with tunning with a exhaust gas temp gauge?
the temp should be highest at stoi(14.7), with a narrowband oxygen sensor
you can tune to certain point from highest egt like -20 C on the rich side or -50 C
to the rich side ,where -50c from stoi would be richer afr.
surely it will be not way as good as a wideband oxygen sensor but
it should be cheap .(lots cheaper)

anyone has one for sell?


chears!

 

[sekut_kring]

Tuning Via EGT vs, Wide Band/ Narrow Band Meters

SOme reading for me and you all....

There seems to be a lot of mystery and misinformation about using exhaust gas temperatures to tune engines. Claims by many EGT gauge manufacturers about it being the best way to tune an engine must be qualified. The BEST way to tune an engine is on an engine dyno- PERIOD. What EGT is good for is a reference for where the engine made maximum torque at wide open throttle. Once removed from the dyno, a similar air/fuel ratio can be established at a later date by dialing in the mixture to achieve the target EGT. It is really the AFR that is important, not the EGT. Most engines will make maximum power at an AFR of between 12.0 and 13.5 to 1 however, the EGT may vary from 1250F to 1800F and is dependent on many factors.

It should be mentioned that the target EGT is valid only on the same engine configuration as was used on the dyno. If you change the ignition timing, cams, pistons, headers etc., the optimum EGT may also change. Raising the compression ratio with no other changes will drop the EGT at the same AFR. Retarding the ignition timing will generally raise the EGT at the same AFR. One engine might make best power at 1350 degrees while a very similar engine might be happier at 1500. You can't guess at this or you are simply wasting your money on the instrumentation. Wankel engines have higher EGTs than comparable piston engines due to their lower thermal efficiencies. 1800F is not uncommon here.

Some gauge manufacturers say you should tune to achieve maximum or peak EGT for maximum performance. This is incorrect. Peak EGT generally occurs at an AFR of around 14.7- 15.0 to 1 on gasoline. This is far too lean for maximum power and is dangerous under continuous WOT conditions. Many people think that the leaner you go, the higher the EGT gets. This is also incorrect. Peak EGT occurs at stoichiometry- about 15 to 1 for our purposes. If you go richer than 15 to 1, EGT will drop and if you go leaner than 15 to 1 EGT will ALSO drop. It is VERY important to know which side of peak EGT you are on before making adjustments. It is safe to say that peak power will occur at an EGT somewhat colder than peak EGT.

You can sometimes feel a lean of peak condition as the mixture is hard to ignite and power will be down a bit as well. Once the AFR gets close to 17 to 1 at WOT, generally the engine will start to lean misfire. Most tuners always recommend to begin jetting or programming from a known very rich initial setting and carefully leaning until torque falls off slightly, then going back richer to the point of max torque. Note the EGT at this setting. Be aware that altitude, barometric pressure and ambient air temperature may affect this optimal temperature to some degree.

Are EGT gauges better than AFR meters? Conventional narrow band oxygen sensors and digital LED meters are not the best devices to measure AFR in the richer ranges but they certainly warn of a too lean condition immediately and obviously, without translation by the driver and they are affordable. Meters combined with wide band sensors are supposed to be highly accurate and everyone has jumped on the bandwagon with these lately. Unfortunately the naive and impressionable often don't question the accuracy of these devices. We have seen some dyno plots indicating best power was achieved at AFRs of 9.7 to 1 on gasoline. This is PHYSICALLY AND CHEMICALLY IMPOSSIBLE and shows that either the sensor was bad (leaded fuel used possibly) or the meter was not calibrated properly. Again, the wide band sensors have the same limitations as the narrow band- leaded race gas quickly fouls them. We have heard and read many stories now indicating that certain brands of wideband meters differ as much as 2 points AFR in readings between each other. In other words, the accuracy of some of these devices is highly questionable. Extensive testing with laboratory quality instrumentation on aircraft engines universally indicates that best power is NEVER made at AFRs richer than 12 to 1. Airflow and fuel flow rates are independently measured and each cylinder is instrumented with EGT probes.

We recently dynoed a shop road racing Celica on a DynoJet equipped with a wide band meter. The meter was saying that the engine was going super lean (17 to 1) at high rpm so we kept upping the fuel there. The engine lost more and more power as we added fuel. The dyno operator was convinced that the meter was right but logic told us with no serious dip in power on the curve and the fact that the engine was still alive that the meter was not correct. We started leaning the engine down more and the engine started gaining power. Finally, when confronted with this information, the operator checked the water trap for the wide band sensor. Once this was emptied, the AFRs looked reasonable again. We didn't need the wide band to tell us this, only the torque curve from the dyno.

We have heard of several other instances with people using wide bands getting erroneous readings and tuning their SDS based on these readings. Then they phone us saying that the system is crap. Look at the dyno curve, when the engine makes its best power at a given rpm, that's where it likes the AFR irregardless of what other instrumentation is telling you. Remember, a bad sensor whether O2 or EGT equals bad information. When the engine sounds crisp and makes great power, you're there.

I would suggest that mixture meters and EGT gauges are complimentary. EGT gauges have the advantage of working long term with leaded fuel which will clog oxygen sensors. EGT gauges are widely used to set mixture on engines used for steady state high power applications where operation has been carefully documented such as in aircraft. The choice would depend on the application. Both are better if you can afford them.



Rgds,

 

[rcchong]

thanks for the reply , for a moment I though it's just quite.
I truely agree that life will be a lot easier wide a 2k wide band
and muilty 10ks(or 100ks?) dyno mechine , but they are really out of my leage
right now.

by your reply few points are comfirmed
1. highsest EGT happened at around stoi ( AFR 15) , add or remove fuel from
there will lower your EGT.
2.wide band need calibration
http://www.megasquirt.info/PWC/calib.htm
3.no , EGT meter is nOt better than a wide band sensor
4.going leaner than stoi will not increase EGT, but is dangerous because detonation
(pinging) creeps in.....
5.I really like your last words:
"I would suggest that mixture meters and EGT gauges are complimentary. EGT
gauges have the advantage of working long term with leaded fuel which will clog
oxygen sensors. EGT gauges are widely used to set mixture on engines used for
steady state high power applications where operation has been carefully documented
such as in aircraft. The choice would depend on the application. Both are better if you
can afford them."
I think we read the same books here , because the EGT tunning idea is from a
airplane tunning corp:
http://www.gami.com/future.html

the story is really simple as I'm trying to built a lean burn machine with water injection.
the whole idea is to save fuel (money) , as I do not plan to 5k modification to save
on 200 bucks monthly fuel . Use what I have and what I can get easily(cheaply),
as I already have the narrow band sensor in my k3-ve exhause , I have thermometer
minus a high temp thermocouple( my thermocouple max at 300 C) , I bet there is
whole lot of data hide in my ecu waiting for me to do some mining , or even a EGT
reading.

btw, I do a search on wide band o2 sensor price , some where say a bosch LSU 4
is for sales at US 80. But how come tuning package price listed here is rm 2k? will
a high end voltmeter works with LSU 4.

again thanks for the reply
ps :EGT is quite high graded for me already, as recently I'm trying to tune the AFR
with my ...... nose , works better after a few drinks though.

 

[ecupro]

Hi, i thing tune first ( on the road ) before you go for dyno.
Friend, Rm 2k is ok like INNOVATE. There build in DATA LOG, and some channels, so that you can see what happen on the sensor, like F1.
Normally, wide band sensor need "CHARGE PUMP" curcuitry.So, i thing just a High Tech. Meter.....I don't work here.
A cheap narrow band o2 sensor and a A/F digital display or LED display will be fine.At least, have a refer....mah.

 

[rcchong]

yah it depends,
some are willing to pay 1k to shave 0.1s for 1/4 time.
while some (like me ?) are trying to find the next rm 10 for fuel....
problem with a narrow band is that it work like tossing a coin,
its rich or lean , for a lean burn operation you need to how lean ?
is it 16, or 18 afr? from a EGT I know that AFR of 18 times will be
cooler than AFR of 16 times.

have fun ...!

 

[ecupro]

Bro, if you use digital A/F display ( not one line led ), you can see from 20 (lean), 19.8,19.6...14.9,14.7,14.4.....12.5,12.3...11.8...10.8..10(rich)
This digital a/f display is a kit form from Australia, Jaycar. or electronic magazine,Silicon Chip.
May be, i can post the pic later.

 

[ecupro]

Bro, here com the pic.
By the way, do not worry my car's coolant temperature, it meter not working.
No money to change one. May be later...it is not safe if my wife want to drive my car.

 

[rcchong]

gees thats nice ....
how's your experince with that ?
I specially needed it on AFR of 15- 20 .
thanks .

 

[hybridnos]

running lean also waste fuel bro..when the engine detect knock..missfiring will occur n start to inject multiply fuel..theres thats why an egt will drop n u waste fuel..n no power.. must go for stoich condition around 14.7 for save fuel..n go for a bit rich around 12.5 for power..



just my 2 cent..correct me if wrong

 

[ecupro]

Bro, not too lean, must take care the engine.

 

[Joeker]

Hybrid,

As a matter of fact, stock ECUs run alittle lean during crusing speed (for fuel economy and emission purposes)

Misfiring happens when sparks fail to arch and the Air Fule mixture is not ignited.

During knock, the ECU retards the ignition timing slightly to compensate.

However, do not confuse between knock & preignition.

Running rich at accleration & WOT also helps cool the pistons.

The general guideline will be stoich at idle, lean at cruising amd rich at WOT.