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Easiest tuning tool..EGT or A/F guage

V
Jan 3, 2008
786
105
43
Eastern Wshington
How likely is a burn down due to heat if the the air / fuel ratios are correct? Pretty much nil? Seems 2 me that EGT gauges are insurance against burning down while the afr is more of a tuning tool. I'm almost thinking that having both would be smart.
 
S

snoboy

Active member
Dec 4, 2007
516
38
28
Maple Valley Wa
How likely is a burn down due to heat if the the air / fuel ratios are correct? Pretty much nil? Seems 2 me that EGT gauges are insurance against burning down while the afr is more of a tuning tool. I'm almost thinking that having both would be smart.

Van Epps you just said it best. Like 4z said... To properly use an EGT gauge requires some baseline work per sled ie. plug readings and piston wash. Once you have the wash and plugs to a healthy point then you do a couple wfos and monitor peak EGTs and then you know what peak is for that setup. At that point you make sure you don't exceed it. My tuning method is pretty lame. My cabin is apx 2500' in the Teanaway, I have always done some WFOs in the big field by the North Fork and make sure sled can do it safely. Then I know I can ride anywhere from Teanaway up through the Esmarelda Basin including Lake Ann without a burndown. I always watch my mid throttle cruising temps on the roads because thats where 2 strokes can get real lean.
 
S
Dec 7, 2007
27
4
3
How likely is a burn down due to heat if the the air / fuel ratios are correct? Pretty much nil? Seems 2 me that EGT gauges are insurance against burning down while the afr is more of a tuning tool. I'm almost thinking that having both would be smart.

Absolutely. I have a race-only vehicle, and work things a bit differently. For starters, I use only the precise same fuel always, from a metal can, pre-mixed the morning of an event, drained (edit: and discarded) between events. Out of fuel? Push/tow vehicle to the trailer. If you run pump gas, even pump race gas, you have to jet richer, for safety, because each fillup will have a different mix in it.

EGT's really don't help you tune. At best, they do two things: First, they help you see if one cylinder is burning hotter than the other. Of course, swap the two probes to confirm this. Some folks need to jet their carbs differently for each cylinder. Second, it can be an indicator that something is going wrong. Record EGT's after each run, noting the values (paper, of course), and if the numbers start to change, figure out why. My EGT's are outrageous, but I know why.

An O2 sensor is, technically, an "oxygen ratio sensor." What percent of the gas that it is exposed to is oxygen. You're not measuring fuel, or air, so it doesn't really tell you A/F ratio, or Lamda. It outputs a value in millivolts. Most units on the market use math to approximate one of these more common values. That's fine, though not very precise. For example, I might be shooting for (a very wrong number) a value of 234 millivolts. What would 254 show as on an A/F readout? The same, I would guess.

Also, I have a separate switch to turn on the O2 sensor's heater, and warm it up for at least 60 seconds before I start the engine. This will dramatically increase the lifespan of the sensor. It would of course be a pain in the rear for a casual rider.

I tune for millivolts. The proper way to set this value is to put the engine on a dyno, then jet for max HP/widest torque. See what the O2 sensor is saying, and that is the value to tune for. You can approximate this with about 400 pounds of math and a dash of understanding, though. No, my number is classified, sorry.

And of course you need to know the weather conditions during this test. Temp, humidity, and barometric pressure. I use a small hand-held weather station for this, that makes barometric pressure predictions. You can enter these numbers (for the day you are about to drive) into a spreadsheet, and jet accordingly. This is complicated for snowmobiles that change elevations. . .

My O2 sensor spends most of its life on a shelf in the shop. I used it to find the perfect tune, and now jet according to my spreadsheet. I install it occasionally just to check state of tune.

Lots of spreadsheets available for free download. Most have a silly element, and ask for both altitude and barometric pressure. I don't understand why. Barometric pressure is all that you need to know. Though I suppose that it will change with altitude, and you could enter the altitudes you expect to see that day, and jet accordingly. . . Hmmm. I guess that these spreadsheets are useful for snowmobilers that change altitude during the day's ride.

And this is only TRULY useful if you have data acquisition, to tie throttle position to O2 level. To jet your carbs precisely. When I first bought my vehicle, anyone but an expert driver would likely burn the engine down. Poorly jetted in the mid-range. I suppose that you could run at 1/8, then 1/4, then 3/4, then full throttle for a period. And glance at the O2 readout, then re-jet and test again. Get close and usually only the main jet needs changing for the day. But again, I don't change altitudes much. My engine can idle for hours, and still have a crisp instant run up to full throttle - it's happy at any throttle position, because I have jetted my carbs correctly.

As you may have realized, I run near burn-down jetting. But then, 1 HP is important to me. Out for fun? Jet rich, be safe, and have fun!

Enjoy!
 
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rmkboxer

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Lifetime Membership
Nov 26, 2007
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Bonney lake WA
The wide band O2 sensor goes bad eventually. So, it is a maint. item, one would have to know when it was starting to fail. They do work well from my experience. The easiest to start off with.

I prefer the EGT probes. No maint and they either work or they don't. I have not had one fail. The down side is there is more baseline work to do before you know what the numbers mean. Sled to sled.

my af gaugae works when it wants too, makes me nervous on a the turbo sled I just bought. but they are cheap enough I am going to buy a new one, they are not water proof, at least the aem isn't. mine has a ton of mousture in it
 

skibreeze

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Dec 4, 2005
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Colorado Springs
my af gaugae works when it wants too, makes me nervous on a the turbo sled I just bought. but they are cheap enough I am going to buy a new one, they are not water proof, at least the aem isn't. mine has a ton of mousture in it

The KOSO is much better as far as no moisture inside goes.
 

Rick!

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Nov 26, 2007
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Ok, so I deserve the beat down on the "loose" EGT comment.

Anywho, lots of good info with the usual mix of experience and experts. In the big picture, a mix of EGT and AFR monitoring would probably give the broadest picture of fueling the engine without having to invest too much money. It seems that Avengers won't do AFR and AFR kit mfr's require higher end kits to multi-task AFR, EGT, RPM, TPS and injector pulsewidth. For carb guys, pulse width is not of interest but the other items are.

Once you get started, like mentioned above, data logging is really useful and reduces your time investment in tuning by easily identifying rich/lean and being able to see where it happens.

For a shameless plug, I use Dynojet stuff; PC V, Wideband Commander with their liquid crystal display (LC 2). Go to their website and see if that is what you want or need. It will log a lot of parameters from the ECU and has the capability to read coolant temp and and EGT - either from the stock sensor or a real thermocouple with a little added box to amplify its voltage. It's spendy, but if you want to play the performance game with new EFI systems, it's dang near mandatory.

For just monitoring and datalogging, it appears Innovate is all over it. I would just check to see if they use heated 02's (preferred).

Bakc in the old days before wideband and narrowband, reading volts on an 02 was mandatory. In general, 0.4-0.6 volt was good for everywhere except for accelerating and WOT. This equated about a 0.5-0.6% CO, exhaust gas and was in the neighborhood of 14-16:1 AFR. WOT wanted a bit more fuel as it keeps things cool enough to promote engine life. This is more in the range of 0.7 to 0.8 volts (1.5% CO to upwards of 4.5% CO, 12-13:1 AFR) on an old style 02 which is still inside the useful voltage output of the sensor. If the sensor says .98 and never varies, then you are too rich. If it says 0.2 or less, you're too lean. .2 to .3 at WOT on a car engine makes for white residue on the end of the tailpipe and for really clean plugs. On a two stroke, it probably means melted aluminum. I never really liked the "Lambda" computed numbers but the germans thought it worked good so they re-interpreted the 0 to 1 volt 02 output into a bigger range for better resolution of computed AFR.

For sure, using an engine dyno to calibrate WOT fueling is the way to go. I've chassis dynoed many engine dynoed combinations and the WOT fueling is pretty darn good from good engine builders.

Of course, there's over the top monitoring and the next level would be detonation sensing. A guy can find DET sensors and displays for about a grand in Japan so for carb guys, that is an option to reduce the sacrificing of a piston and cylinder while finding the EGT limit of your particular combination.

Here's a little chart I conjured up, I'm pretty sure speedytoes top secret voltage number is in here. :face-icon-small-hap
 

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milehighassassin

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Nov 16, 2005
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Tune with piston wash and plugs. After you get that dialed in you can use egt's to stay safe. Like others mentioned, not all motors will be the same. One sled will burn down at 1100 while another will run perfectly all day long.



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hivoltagesledhead

Well-known member
Premium Member
Nov 27, 2007
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Nakusp, BC
I have egts with two probes and an AEM afr gauge(that is always full of moisture) and I am still looking for that sweet spot. My sled likes to run hot and the afr is all over the place. My plan was to use the afr to tune and then see what temps the egts were at. Once that is known,the afr is redundant.
 
S
Dec 7, 2007
27
4
3
There are three or four sets of pictures for 2 stroke piston wash, shown on a couple of dozen sites. They show lean, perfect, and rich wash patterns. Seek and you shall find. If I didn't use a dyno to tune, I'd use piston wash. Remember, you have to do "chops." Run at 1/2 throttle, then kill the motor. Kill, as in turn the engine off while still at 1/2 throttle, and roll to a stop. Then stick a fiber optic flashlight ($6-$15) tube down the spark plug hole. Kinda hard to see in the bright snow, though, I suspect. . . Maybe bring a thick tarp to drape over you and the engine, to be able to see it.

If you run high quality race gas, reading plugs doesn't really help you any more. Still good for pump gas and (maybe) low quality race fuel.
 
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