I got this from The SDS Site, but it's very good info.

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 the 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 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 11.8 and 13 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 laboratory quality usually, highly accurate and useful but very expensive and sometimes bulky. EGT gauges have the limitations above and are generally priced between the other two. I would suggest that the two types 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.

All this is courtesy and copyrighted by Simple Digital Systems EFI http://www.sdsefi.com

WD

I'm not sure that Nissan guys are aware of it, but like it says on here, us DSM guys almost always use EGT over narrow band O2 sensor (I would never use a narrow band for tuning). Not only will EGT help with A/F, but it will help let you know if you IATs are getting too hot which will/could cause knock.

npaulseth wrote:I'm not sure that Nissan guys are aware of it, but like it says on here, us DSM guys almost always use EGT over narrow band O2 sensor (I would never use a narrow band for tuning).

none of the DSM guys i know do.

Quote »Not only will EGT help with A/F, but it will help let you know if you IATs are getting too hot which will/could cause knock.[/quote]i'm almost positive that i've touched on this subject before. if your trying to achieve your goal AFR based on your EGT, then your asking for trouble. your EGT and IAT relationship is just way off base.

Quote »Why not tune AFR based upon EGT (Exhaust Gas Temperature)?You can only get a general idea of AFR based upon EGT IF, and only if, you have correlated your car's AFR with its EGT under a given set of conditions. And even at that, you can only get a general idea of the AFR. You can not tell with accuracy just where the AFR is. Perhaps at best you can get within a full point or so, and that's not very close.

Here's an example of the variation in EGTs from car to car. Several months ago I helped tune 3 single turbo Supras on the same day on the same dyno using the highly regarded Horiba wideband O2 system. All 3 cars were tuned to about 11.4:1 AFR across the boost and RPM range. Peak EGTs ranged from 770 to about 880 C on the various cars according to the GReddy gauges (one car's EGT at 770, one at 790, and one at 880). All 3 had GReddy EGT gauges but with identical probes mounted in different places. The coolest EGT reading was from a probe mounted in the #6 runner, the middle temp one was mounted in the front passenger corner of the collector, and the hottest reading came from a probe in the center of the collector directly under the turbine inlet. This in itself proves that EGT readings can not be trusted because there is no physical way that the EGTs in the collector are actually hotter than those in the runner close to the combustion chamber, but this is a function of heat-sink effect happening with the probe and we won't get into that concept here.

If one were attempting to tune the above cars based upon EGT readings, what would he have done with those 3 cars? Conventional wisdom says that EGTs of up to 900 C are allowable prior to the turbo on most turbo motors. If the 770 C car were leaned out to approach 900 C, the AFR would have been in the 15:1 range! That could prove disastrous for an engine running boost. A similar circumstance exists for the car indicating 790 C. What about the one with the 880 C readings? Would that car be dialed back a bit richer because the 880 C readings are approaching the generally accepted MAXIMUM of 900 C? If so, that car would probably end up in the 10.5:1 range and needlessly sacrifice power.

Perhaps the biggest downfall of EGT as an AFR tuning tool is the fact that there is no possible way for an EGT monitor to react quickly enough to spot lean and rich spots in the RPM curve. Most engines will exhibit an AFR curve that varies a good bit throughout the RPM and boost range. At best, EGTs can only give you some indication of peak temperatures. It is not possible for them to point up a dangerously lean area spanning a few hundred RPM somewhere in the range (even though many cars exhibit AFR curves of this sort that need to be tuned to flatten them out).

The bottom line is that EGT readings don't really provide much useful information when it comes to AFR.[/quote]stolen from this FAQ

-demetrius

An EGT gauge comes in real handy when adding Alcohol or Methonal to an already tuned mix. Since both will seriously drop your EGT's. Its hard to tune alky with just a wideband do to the octane difference. Since 11's would no longer be your goal under boost. Propane is another...

WD

this is great info. seems that the fog over having an egt gauge has been lifted.

demcj wrote:none of the DSM guys i know do.

Really? I'm from MN and a lot of the DSM guys that make any decent power have an EGT gauge. The guy who I just sold my laser to put an EGT gauge in his mostly stock AWD. I'm not saying it's manditory, but it's really a nice thing to have. A lot of supra guys have them to monitor things when doing highway pulls.

npaulseth wrote:A lot of supra guys have them to monitor things when doing highway pulls.

monitor is the key word here, and that's only after you've tuned on a dyno to know what's acceptable for your engine's setup.

-demetrius

WDRacing wrote:An EGT gauge comes in real handy when adding Alcohol or Methonal to an already tuned mix. Since both will seriously drop your EGT's. Its hard to tune alky with just a wideband do to the octane difference. Since 11's would no longer be your goal under boost. Propane is another...

WD

i've got no experience with alcohol, methonal, or propane injection. don't you have to run 2 different maps? is injection that detonation resistant that you can get away with using EGTs as a guide?

-demetrius

It really depends on if your using Alky/methonal/propane as a fuel or simply as a knock deterent. If it's done as a fuel source then you need two seperate maps for tuning, but for detonation you can use a egt gauge to show the onset of heat removal and the extent of the removal, thus showing how much more boost you could run.

Me, I run enough alky/propane/methonal to bog the motor, then slightly reduce that amount and add boost. I don't have an EGT gauge. But I know many others who use the method I described above for adding a secondary injection.

WD

demcj wrote:monitor is the key word here, and that's only after you've tuned on a dyno to know what's acceptable for your engine's setup.

-demetrius

Just to add on here, the primary reason to have a gauge in the first place is to monitor the vitals. Trying to tune a car is very difficult by looking at guages. Try watching a tachometer and an EGT(or an wideband O2 for that matter) at the same time while driving and tell me you can figure out what changes need to be made and at what RPM. I doubt you could. Hell, I've tried. Datalogging and making adjustements after a dynorun is probably the most popular way to properly tune a car. Tuning realtime on a brake dyno would be even better but few of us would ever have access let alone ever see one in person. Be wary of anyone who will tune based on the guages in the car.

Guilty....

So, for my application(FMU, no tuning options) which gauge is better for monitoring AFR's?

demcj wrote:none of the DSM guys i know do.

Previous DSM owner here and I used EGT. Most of the older DSM owners used them. Now that the wideband o2 sensors are more readily available, more people are using those. Either one of them are highly effective at maximizing your current setup.

Quote »i'm almost positive that i've touched on this subject before. if your trying to achieve your goal AFR based on your EGT, then your asking for trouble. your EGT and IAT relationship is just way off base.

stolen from this FAQ

-demetrius[/quote]Coming from a company that specializes in selling Wideband o2 sensors, I find this highly unreliable.

WDRacing wrote:If it's done as a fuel source then you need two seperate maps for tuning

As a fuel source you need to run it in it's own fuel setup, ie. pump, injectors (which have to be about 2-3 times as large as you need for pump gas), plugs, and ignition / timing maps.

Otherwise you are cheating yourself out of the many benefits of running a cold fuel.

Also bear in mind that methanol likes compression ratios above 15:1 and it's AFR's are extremely rich for accurate combustion. You should run the engine a little fat to get some expansion in the exhaust manifold to make up for the lack of post combustion EGT.

WDRacing wrote:but for detonation you can use a egt gauge to show the onset of heat removal and the extent of the removal, thus showing how much more boost you could run.

By the time your EGT gauge reads severe exhaust warming from detonation it's already too late. Not too mention methanol can act as a coolant and retard this signal further. I would suggest getting a knock meter rather than wasting money on the EGT setup.

jmauld wrote:Previous DSM owner here and I used EGT.

so you tuned your car just off your EGTs? no dyno tuning, no AFR meter/wideband o2.

-demetrius

demcj wrote:so you tuned your car just off your EGTs? no dyno tuning, no AFR meter/wideband o2.

-demetrius

It's not particularly easy to dyno tune an AWD car when the closest one was 500miles away, at the time.

I used EGT, monitoring Knock, track time and common sense. In the end, it ran a 13.2 in the 1/4 mile with no more then $800 in power mods. This was on a car with 120K miles and the original engine.

that's scary.

-demetrius

Explain why it's scary? I put over 30K miles on it, with basically the same setup, and I drove the piss out of the car. Sold the car, and the following owner never reported any problems with it.

* I should say I never had any engine problems. Transmission problems were a different story.

Also, you have to remember, 5-8yrs ago a Wideband O2 wasn't nearly as available as it is now. The same is true for Dyno time.

EGT was (and still is) a valid way to tune a car. Literally thousands of DSMers pushed their cars well past a 13second 1/4 mile with nothing more then a boost and EGT gauge.

I'm not arguing that a wideband o2 isn't a better optoin, just that EGT shouldn't be dismissed. Realize that there is a lot marketing hype that is being preached to get everyone to purchase a wideband.

jmauld wrote:Explain why it's scary?

for the simple fact that EGTs are not accurate. there are just too many variables that can come into play. i can understand doing what you did to get a setup up and running, but not to rely on it completely. but hey, you can't knock it if it worked .

-demetrius

an afr gauge.

-demetrius

jmauld wrote:EGT was (and still is) a valid way to tune a car. Literally thousands of DSMers pushed their cars well past a 13second 1/4 mile with nothing more then a boost and EGT gauge...

Yes....but they have an ECU tuned for boost from the factory - That can ACTIVELY pull timing based on knock.

Try tuning a Nissan (specifically an S13/S14) that has been turbo'd with just EGT.

Now, you cannot monitor knock, the ECU gives timing based on airflow and TPS...and does not "pull" timing if there is knock. And the motors are 9.5:1 with relatively fragile pistons...

DSM's can take a little abuse, some knock...and live to tell the story. Not the case with a KA.

And DSM motors are WAY less detonation prone due to lower static compression and active knock control...

Given the SAME EXACT setup for a KA-T and a DSM...you could get +300rwhp safely and reliably out of the DSM using only EGT to tune with an S-AFC...not so much with a KA.

...and what the EGT could tell you in the process will tell you too late for the KA.

- Brian

whoa.. still so much to learn... and thanks to all who freely share thier insight with the less kinowledgable (sp?)-g

EGT's are overrated. You can't tune well with them, and by the time they are too high the engine is already ****ed.

Get a wideband, or a real datalogger.

In my opinion EGT's are pretty useless. Bottom line, you can't reliably, accurately, and safely tune a car with them. Yeah you might try and it might work, but that doesnt mean that its a good idea and that its actually tuned well.

EGT's can help when involving other things, like methanol and propane

also when they are high there are different things for that. i always thought very advanced timing would make them very high, when i was figuring out my timing i found that very retarded timing would make them shoot up (combustion happening later) i never really look at mine much anymore but will be once i get my methanol kit hooked up

Only thing I know of that should be tuned with EGT is a diesel.

Yea WD, I love that http://www.sdsefi.com I go there once a day and just read stuff.lol Along with http://www.stealth316.com Both excellent tech sites.