AFR or EGT

[chrishew]

I'm going to be installing a full AAEN exhaust and a Boondocker Box on my 12 Pro 800 RMK this fall.
Been wondering whats the best feedback to go with to tune the fuel map.

I've used dual exhaust gas temps in the past on my old carbed machines but haven't tuned an EFI machine before.
There are so many different throttle position and rpm ranges to make fuel adjustment in I wasn't sure if the EGT's would respond quickly enough to see where lean or fat spots may be.

Been thinking a wideband Air Fuel Ratio gauge may be the way to go instead, since it should give you a more responsive indication.
But guys say the AFR sensors don't last that long and the C16 race gas for my BOSS NOSS kit definitely won't extend it's life.

I know you start by reading spark plugs or piston wash but that isn't easy to see for every throttle position and rpm range, mostly just for wide open under load indication.
Also I've only ever used my spark plug colour, how does a guy read piston wash?

My EGT's were mounted 6-8"s from the exhaust flanges but I can't seem to find anything about the best spot to locate an AFR oxygen sensor?

 

[Modman]

I'm going to be installing a full AAEN exhaust and a Boondocker Box on my 12 Pro 800 RMK this fall.
Been wondering whats the best feedback to go with to tune the fuel map.

I've used dual exhaust gas temps in the past on my old carbed machines but haven't tuned an EFI machine before.
There are so many different throttle position and rpm ranges to make fuel adjustment in I wasn't sure if the EGT's would respond quickly enough to see where lean or fat spots may be.

Been thinking a wideband Air Fuel Ratio gauge may be the way to go instead, since it should give you a more responsive indication.
But guys say the AFR sensors don't last that long and the C16 race gas for my BOSS NOSS kit definitely won't extend it's life.

I know you start by reading spark plugs or piston wash but that isn't easy to see for every throttle position and rpm range, mostly just for wide open under load indication.
Also I've only ever used my spark plug colour, how does a guy read piston wash?

My EGT's were mounted 6-8"s from the exhaust flanges but I can't seem to find anything about the best spot to locate an AFR oxygen sensor?

Personally having had many sets of both, I prefer the AFR. Its real time, its more accurate. EGT's can give false positives easily and are not always the best accuracy based on the placement. There is a lot of good info on plug reading on the internet, you really want to do a plug chop with a new set of plugs and read how far up the porcelain the fuel ring is. This requires cutting the threads off the plug to see it clearly. Also how the colour on the base ring and electrode look, electrode is more timing, the base ring is jetting. Piston wash takes a lot longer to develop (days and weeks), to get it accurate, its not instant like plugs.

You will not get the same life out of an AFR sensor, that is correct. They don't like lead either. That being said, if you are just setting it up and then don't intend to dick with it all the time, once its set up, the AFR becomes redundant basically, and could be removed, if the sensor messes up its not big deal if you aren't going to change anything in the fueling set up. My recommendation is to buy a generic gauge like an AEM for a car and silicone the piss out of it, even if you have to use a rectifier to convert the voltage (about $3) from AC to DC on your sled, its a super easy hook up. Most sleds are coming DC now though with rectifiers installed already, not sure what yours is but easy to figure out. Silicone will help keep moisture out, but it gets into them all, no matter what. The generic gauge will allow you to use a generic sensor from Napa, which down the road will save you a lot of $$$ if you want to use it all the time and are using C16.

Best spot for an AFR mount is the top 1/2 of the pipe so that the sensor angles down to some degree, this helps to drain any moisture/fuel out of the sensor, and in a straight place on the pipe (not on the inside or outside of a bend).

 

[chrishew]

Awesome Modman. Exactly the info I was looking for. Thanks a bunch.

 

[Stg2Suby]

Great input by Modman. FWIW the wideband AFR sensor on my M8T went close to 1000 miles on 100LL avgas before starting to show the odd error code.

 

[Chrisco]

So what a/f number would be considered lean or close to burn down at WOT on a 2 stroke? This has always been the unclear subject. Any info would be great.

 

[Modman]

So what a/f number would be considered lean or close to burn down at WOT on a 2 stroke? This has always been the unclear subject. Any info would be great.

My engineer buddy and I have discussed this on numerous long truck rides....he is a 4 stroke guy on av gas and me the 2 stroke guy on av gas. AFR is a reading of voltage between the CO and fuel levels in exhaust, and that voltage is converted into a theoretical calculation of how much oxygen would be required to complete the combustion process at stoichiometric ratio 14:1 (only theoretical based on the sine wave map).

Some of the thought/theory is because 2 strokes are inherently sending unburned air/fuel mixtures out the exhaust port (due to the port timing, exhaust pulses and pipe scavenging), in theory the readings should be showing a "leaner" condition as the theoretical math/conversion/calcs completed by the gauge and voltage are influenced by the the idea that the gases coming through would be completely combusted, and should/would be only giving you the AFR reading of the incoming mixture that was completely burned. The differential is the unburned mix that goes out the port, which will be different for all sleds. 4 strokers would never run this lean (12:1 is the ideal 4 stroke ratio I am told...). I don't know enough of the theory behind it to fully understand it, ultimately the value on the gauge should be correlated to a plug reading as too many factors can be influencing each individual sled (port timing, fuel type, probe placement, throttle position, ignition timing etc etc).

All that being said, I think the newer 2 strokes are far superior with the power valves/RAVEs, EFI, etc etc and I find that my new sled is pretty close, I run about 12.5 mid range and the plugs look good, and at WFO it hits as low as 10.5, and this year I intend to trim that a bit closer around 11 as you can tell by the plugs and how it runs that its got a little bit extra fuel there. Since more heat is generated as you move up the RPM range, as a safety margin I don't think i'd be shooting for 14 at 8000 rpm.

 

[Chrisco]

Right ..... the new sleds running up the trail get as high as 13.5 and some hit 14 on the air fuel. WOT I think you would like to hit 12.5 to 12.7 is what I have found. I have never had the pleasure of blowing up my sled with a A/F on it to find what the magic number is. 10.5 on a 2 or 4 stroke is extremely rich. I still like to run a EGT gauge it just seems to be more clear (to me) But I think If you stay at 12.1 to 12.5 WOT I think your on the money.

 

[chrishew]

I have also heard that 11.5-12.5 on a 2 stroke is a nice safe range to be in.