Rather than just buying a bunch of after market parts and slapping them on, I want to be able to tune for best performance and reliability.

In order to do so, which method should I select, EGT or Air/Fuel Ratio?

Would certainly like to hear opinions and pro's/con's for both methods.

no replys? come on guys some one has to have some input on this. i would say egt because its more acurate to engine causing damage,but i dont have a lot of experience with either

yea dual egt's is the way to go... gotta keep an eye on em tho, if not you will be a sad lil panda for sure!

best method is looking at piston wash and tuning on a dyno...

egt's and piston wash more importantly.

I love my wideband A/F gauge. It is the way to go if running a single pipe and a muffler. If running multiple pipes and individual silencers, then I would go with egt's, as one pipe could be leaner than the other(s).

AF Ratio is the most accurate for sure. If your fuel injected it's the cats ass, No pun intended. EGT's can be low and burn your sled up because of to much fuel wuth the AF ratio it's dead nut's. Good luck!

HUH? I'd like to see a burndown from too much fuel...lol

Tell me how exactly an A/F ratio on a 2 stroke engine is most accurate(over egts and piston wash) and then tell me how if you were running optimium fuel to air ratio how does that equate to a engine not being in burn down territory? 2 and 4 strokes are different especially when talking about exhaust because #1, 2 stroke exhausts pulse back and forth(flame travel) as well as they inherintly always dump raw fuel into the exhaust due to the basic 2 stroke design. So how can you accurately tune an A/F ratio when you have unburnt raw fuel in a 2 stroke exhaust constantly? I dont see how that can be considered accurate or most accurate.

If we were talking 4 stroke then yes A/F ratio can be used to propely tune a engines fuel/air ratio.

im with gpxsrxracer... with a good egt gauge and fast response leads... theres no way your gonna get that accurate of a reading through an A/F gauge.. your better off doin plug readings in my book

Don't waste the money on EGT's they don't tell you what you are actually looking to find out. You'll be much farther ahead with the O2 Sensor. Reading plugs is a crap shoot. They don't respond fast enough to changes made in fuel delivery.

please explain...how are you further ahead on a 2 stroke engine?

gpxsrxracer,

I was a true believer in EGT’s until this winter. I ran them on previous sleds and they were a good tuning tool but they don’t take into consideration many of the other factors that affect fuel delivery. Sleds these days have the ability to adjust the timing curve of the motor on the fly. With changes in ignition timing come changes in exhaust gas temps. If you back the timing down you will throw more heat out the pipe and think you are leaner when in reality that is not the case. Fuel types can also affect EGT readings. Engine compression, ETC. ETC. Heck you can actually get to a point of having low EGT readings because you are too lean. Scary to think! There are other factors as well that can affect what your readings are but it all comes down to one simple thing. A wideband air/fuel ratio meter tells you directly what you need to know to tune your fuel delivery. It tells you the amount of oxygen and fuel left over from combustion. This is what you need to know.


I hope this helps


Regards,

MNF1000

MNF1000, re-read this post. Untill you can explain to me how this can be accurate when you inherintly have raw fuel dumped into the exhaust on a 2 stroke(dam near impossible to get around this) how can you say you can most accurately tune on A/F ratio alone on a 2 stroke? Were not talking 4 stroke here.

I understand how they work, but I strongly disagree with them being most accurate when your talking 2 strokes...unless you were running a HPDI engine(injectors in the cylinder head) which isnt in any production snowmobile I know of to date, there is no way around getting unburnt fuel in the exhaust and getting an accurate reading.

Gpxsrxracer,

I re-read the post that you quoted and I’m not 100% sure what your actual question is. You stated that raw (Atomized) fuel does enter into the exhaust system and I would certainly agree with that. But this unspent fuel and oxygen is what is measured by the O2 meter and is then put in terms of a ratio with oxygen. This gives you the measurement of air/fuel which is ultimately what you are trying to achieve. I’m actually running EGT’s and an O2 meter on my sled right now and the only thing that I use the EGT’s for now is to trim the cylinders so both are running at nearly identical temps.

I apologize if I misunderstood your question and would be happy to try and elaborate on this more but I’m not sure what you’re asking. Were both referring to “Wideband” O2 sensors right?

I reference a simple dyno sheet for example. BSFC- Brake Specific Fuel Consumption as well as air/fuel ratios are commonly shown to communicate how lean or rich a motor is running at a given RPM. It has been quite some time since I have seen EGT’s shown on a sheet to aid in the analysis of tuning. (This is mostly in part to the fact that people don’t run EGT’s into the Dyno interface for comparison.)

Why is it that you feel EGT’s are more beneficial to tuning as apposed to an O2 sensor? Have you had the chance to tune with an O2 sensor and compared your findings to that of EGT’s. Not trying to start an argument here but rather find out what your thoughts on this are.

Thank you,

MNF1000

I have EGT's on my sled and I do like them. Once again they are a tool that is to be used to help you get your engine to the right place it should be. I have seen low readings when there is not enough fuel, lean condition and I have seen hot readings when there is to much fuel, rich and burning in the exhaust. I also have seen a A/F guage that was reading perfect on the guage, but when we pulled the plugs we found it ready to burn down. Both EGT's and A/F have their place, they are a tool, to be used to help once you get a baseline reading on plugs and piston wash.

A/F. EGT's are a thing of the past.

how is it a thing of the past?

If you are trying to improve your engine then they are a important tool in you doing that.
My sled the stock settings were rinch on the bottom and top but lean in the middle. You find
tune your settings and you pick up some power.

for those running the wideband, where do you mount the sensor? in the silencer or near it?? i'd think it would be best for it to be past the expansion chamber...

i've been thinking about adding a wideband o2 setup, who's setup does everyone use? i'd actually prefer a small digital readout instead of an analog.

That Girl, I know how well your sleds run so please dont take this reply as disrespect by any means...

Do you tune with A/F ratio only? No piston wash or plug readings?

I disagree with saying A/F ratio is best on a 2 stroke, best being the word here. If we were talking 4 strokes, thats a different ballgame and I would have to agree A/F ratio all the way on a 4 stroke.

I posted this earlier, but as most know, on every 2 stroke unless its direct injected they inherintly dump some raw fuel into the exhaust, dam near impossible to get around. So when exhaust exits into the pipe its mixed with raw fuel and not the true A/F ratio the engine puts out, so its the A/F ratio of the engines exhaust plus the inherant raw dumping of fuel also at the same time. For those who dont understand there are many 2 stroke engine simulators on the web that will show how there is wasted unburnt fuel.

Link to one basic example http://www.keveney.com/twostroke.html

So how does one get a true accurate A/F ratio when you have the exhaust of the engine plus the raw fuel that also gets dumped into the exhaust on every exhaust downstroke? I personally cannot call what comes out the pipe an accurate description of the true A/F ratio form the exhaust of the engine knowing this.

bingo!, bikes (4 strokers are a good example here), too little fuel, they'll run, but like shit, cooler pipes (confirmed with both gloved hands and temp guns), but,,,, on a 2 stroker, keep it lean (but close to being perfect, BUT STILL ON LEAN SIDE) and it'll smoke the domes quicker tha Monica smoked Billy's dome in office < fact

If there is "raw" fuel coming from the engine I should be able to go out right now and take my pipe off and dump out this "raw" fuel. Here's the thing... Yes there is going to be more unspent fuel coming from a two stroke but that is the nature of a two stroke. You just tune with that in mind. Simple as that. You aim for a number that is richer (12 - 13) instead of a 14.7 that a four stoke might see. (Keeping an eye on piston wash and plugs too.)


The long and short of why O2 sensors have not previously seen use on two stoke engines is due to the fact that two stokes carry the oil with the fuel and the oil can have a tendency of shortening the life of the sensor. If you’re running a wideband O2 sensor it is critical that you monitor your oil ratio to extend the sensors life. How does something new get introduced to an industry anyway? Does it just magically appear? People try it and experiment to see what works. These just work.

Both systems have merit it just boils down to what you prefer to run. I've run EGT's for the past six years and an O2 sensor for about one season. I won't be installing the EGT's on any sled in the future. Especially something that is EFI.

gpxsrxracer - have you ever run an O2 sesnor on your sled?

MNF1000, no I havent used them on any 2 stroke. I cant say I never will, but no. What you did post strengthens exactly what I have been saying all along. If you cannot shoot for 14.7 and you have to compensate to 12 or 13, I wouldn't consider that most accurate. So what true number is most accurate? What would be the most accurate number for a 2 stroke? I can tell you O2's werent developed initially for a 2 stroke engine. Its something that was developed for a 4 stroke engine and then recently applied to 2 strokes.

Can you make it work, yes I think so, but not as accurately as if you were useing it on a 4 stroke. I would still have to say piston wash is #1 along with plug readings.

I know what your saying with EGTS, one engine can live happily at 1250 degrees where as another can live in the 1300's and its not accurate or the same with every engine as some burn down at higher temps and some lower due to squish, timing, fuel, pipe, ect ect. Believe me I know the faults that egts have as well. Plus proper placement of egt probes is critical, which also changes accuracy.

Would I try a A/F setup, yes but I still cant accept this to be most accurate. I guess it can be used in cunjunction with piston and plug readings then see what your running A/F ratio wise with good plug and piston readings, same as I would do with EGTS, see what my plugs and pistons look like and then see what I'm running for egts.

You’re not compensating to a 12 or 13 as apposed to 14.7. 14.7 is where a typical four stroke would run and that is what everyone thinks about when they think 02 meters. This doesn’t mean a thing when using it on a two stroke. Two totally different induction principles. I know you understand that and that is why we are having this discussion. So that doesn’t strengthen anything it just goes to show you that the different types of motors require different Air/Fuel mixture values. You’re comparing apples and oranges. As for the comparison of the E-Tec and how that is closer to 14.7 that is only because of the different induction method. The motor can run leaner because of how the induction and lubrication method works.

I’m getting off topic here but the question that was first asked was “EGT’s or Air/Fuel Ratio and which is better for tuning?” In my opinion and personal field tuning experience the Wideband Air/Fuel meter is better for the following reasons.

1. Air/Fuel ratio has fewer variables that can change its value as apposed to EGT’s. Air/Fuel values are not going to significantly change with differing fuel types or ignition timing changes like they do with EGT’s. Resulting in inaccurate readings.
2. Air Fuel meters have a better ability to show a pipes scavenging ability on different types of terrain when located in the muffler. For example. On a lake surface with 4-6” of grainy loose snow I have seen meter readings of 12.6-12.8. in 2000 feet. Take that exact same sled and run on a hard packed road at the same distance and I saw 12.8 to 13.1. This is a direct result of increased pipe center section temps and the load placed on the motor in a given distance. Bare in mind my EGT’s were reading 1180-1220 on both runs with no noticeable change based on load to the motor.
3. Personally I find it easier to look at a three digit number on the 02 meter when running at high speeds as apposed to four digits like commonly found on EGT’s. When you are riding and trying to concentrate on what is going on in front of you and look down to see what the motor is doing I would rather glance at the 02 meter than stare at the EGT ‘s.
4. An O2 meter it is much easier to correlate Dyno sheets and Brake Specific Fuel Consumption numbers as where as EGT’s are rarely used on dyno’s.
5. Finally when comparing the two tuning tools I like the O2 meter better because it is a direct method of measuring what you are trying to tune. The fuel and air mixture. Be it an O2 meter or EGT the ultimate goal is to determine the correct amount of fuel and air to be delivered for optimum combustion. That is what the 02 meter tells you. Not an indirect reading that can be affected by many other variable like EGT’s.

Good discussion.

Regards,

MNF1000

Is there a good reference for reading piston wash (detailed - preferably with photos)? I'm going asphalt racing for the first time this year, and I have no idea where to start for a baseline. I know how to read a plug, but at a dragway where you HAVE to run the machine at less than WOT after a pass, I think that plug readings will be useless.

Does this A/F vs EGT discussion apply to older iron as well? My machine is a 97.

Thanks!
Scott

One thing to realize with Wideband Oxygen sensor use, is that it is only reading the average of all cylinders unless you have a sensor and meter for each cyl/pipe. Imagine trying to find which carburetor has water/ice/dirt in it with a wideband reading or with EFI, which injector is not working well. Worse yet, imagine a misfiring spark plug in an EFI auto causing the sensor to see a rich condition and leaning the air/fuel ratio down on all cylinders when in closed loop mode. At least EGTs can be used inexpensively/easily in all pipes to help see this and can facilitate any necessary stagger jetting. Even EFI has an ability to be stagger jetted on a sled if using a Boondocker (or equivalent) tuning box.

Oil or Leaded racing fuel also can damage the sensor rather quickly.

EGTs are valuable for other reasons such as avoiding too much exhaust heat at the entry to a turbo turbine inlet.

Another concern is the effect that any exhaust airleaks cause with misinterpretation of air/fuel readings.

Bottom line: Neither system is foolproof. Both systems are useful and beneficial if limitations are considered.
I'd use both systems myself.

go to John Hoopers Web site... He states on there to not even ask him about EGT's. Hooper builds some really good stuff.

I am getting both for my sled this year. Running in the stock class this year and i need all the little power i can get.

Why not run both???????

In my understanding EGT's are really meant to monitor a known set up. You have to find the right number for your particular set up by reading piston wash and plugs and then look at the EGT readout to get the number. This could lead to different numbers in each cylinder, because the piston wash and plugs tell you when the set up is spot on. You could fine tune a known set up, but you wouldn't want to install some probes and jet to a number that somebody gave you because every engine and probe placement is unique, so every correct EGT reading is unique to that particular sled and set up.

I'll chime in here for a second.

A wide band sensor reads the amount of O2(oxygen) in the exhaust and not the fuel, it's the amount of O2 thats present in the combuston chamber(fuel mixture) that causes a lean condition and causes burn downs.so there kinda related

When we are dynoing a engine, we use many methods,wide band,EGT's,air hat,BSFC,plug reading,piston wash, the list goes on.

It also depends on what the goal is of the dyno runs, if it's a new combo then we run the whole setup, if it's a known setup with small changes then we'll run the O2 with egt's and BSFC,
So why EGT's???well they will show if there's a embalance between cylinders,Like if there's a plug going down or a carb balance problem.

But even with all those toys we still will go back to plug reading and piston wash, plugs can show you many things about a engine that sensors can'tl.

The point is, if a person relys on only one thing to tune a engine, then you'd better buy more pistons

Use a combination of methods, egt's, piston wash and plug reading or Wideband,piston wash and plug reading, in the end it's your ability to understand what your looking at and how to correct the problem not the methods your using.

Cliff Yeatman
Advanced Dyno

ski doo di 600 tnt,yes direct injection so now you no

Ill bet you I can burn down your engine with an EGT guage that show that you are in safe territory. And on the other hand I can get you to jet an already pig rich engine, according to the EGT guage, even richer........

Here is a question for you EGT users, change your timing and what happens to the EGT? If you have an EGT reading of 1800 degrees are you too lean? Go from stock pipe to aftermarket what happens? The correct stochiometric ratio for a carberated sled is 12-13, carberated 4 stroke 14.7, fuel injected 4 stroke 15.7.

EGT's are good for seeing what is happening in the motor for timing changes, not jetting. What are you trying to accomplish by jetting your carbs, the correct air to fuel ratio, right. So why would you use an EGT. Example, engine is pig rig and dumping fuel out of the port, hot return gases hit that unburned fuel and ignite it, what are your EGT's going to say.....WOW HOT, so what are you going to do, jet an already pig rich motor even richer. If you are even going to attempt to use EGT's to jet an engine you should A: do it on the dyno, B: have 1 in the head pipe, 1 in the convergent cone, 1 in the divergent cone, and one in the stinger section. So that is 4 EGT's in each pipe and you will have to know what temps are optimum at each section. EGT's are a tool, just not for correctly jetting an engine, just like an A/F sensor is a tool. I wouldnt use an A/F sensor to tell me what is my peak rpm. So, if you are looking for correct jetting (A/F ratio) use an O2 sensor

so how were people building mod engines and sled motors dirtbike, and better yet drag cars before 1990 came around and someone decided to invent an o2 sensor... they looked at the spark plugs piston wash and used there nose and ass!!! just takes much more skill that way then looking at a gauge ive seen more shit blow up with both methods of monitoring the gauge and sensor is only as smart as the operator... you can go ahead and trust some 9 dollar sensor or gauge that was built over in f*in honduras by some 9 year old but good luck to you! both of these methods have their ups and downs it is prefrence an AF gauge is more "fool proof" in my mind its a number readout and your correct saying you can get cold readings on an egt from being too lean but if you look at your piston wash you would know that your top end was about to liquify into the pipe... both methods are effective