Easiest tuning tool..EGT or A/F guage

Van Epps

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Easiest is not the word I should have used. Going to start tuning a motor and am wondering which type of gauge is the more helpful / better tuning tool.

I'm running a single pipe and wondering if it's ok to use a single probe egt probe at end of y pipe? Can a guy even use a double probe gauge with a single pipe? Don't think so but not sure.

Thanks
 
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Summit8

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Don't know what is considered better between egt and a/f sensors, I've got 2 sleds with Digatron dt-33 gauge I believe it is and they work very well, you see both egt's and can switch the 3rd window between water temp and rpm w/ setable limits on all 3 windows, 2 egt probes in the y-pipe.
 

Mjunkie

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I haven't ever used the a/f system, but I would think it is a much more accurate way to tune. It will tell you the ratio, EGT's will only tell you how hot it is, not neccesarily what your mixture is. I think EGT's are more for reference than for straight up tuning, but that's my opinion.
 

4Z

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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.
 

snoboy

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Air/Fuel ratio. I've been told it's the way to go for tuning. I've had an Avenger I single window on the my last 2 sleds. It uses 2 probes, 1 in each leg of the Y pipe. I leave it set on max so it always displays the hottest cylinder. Just one more thing for me to dick with and keep my eye off the road. ha ha
 

4Z

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Air-fuel ratio (AFR) is the mass ratio of air to fuel present during combustion. If exactly enough air is provided to completely burn all of the fuel, the ratio is known as the stoichiometric mixture (often abbreviated to stoich). AFR is an important measure for anti-pollution and performance tuning reasons. Lambda (λ) is an alternative way to represent AFR.

A stoichiometric mixture is the working point that modern engine management systems employing fuel injection attempt to achieve in light load cruise situations. For gasoline fuel, the stoichiometric air/fuel mixture is approximately 14.7; i.e. the approximate mass of air is 14.7 mass of fuel. Any mixture less than 14.7 to 1 is considered to be a rich mixture, any more than 14.7 to 1 is a lean mixture - given perfect (ideal) "test" fuel (gasoline consisting of solely n-heptane and iso-octane). In reality, most fuels consist of a combination of heptane, octane, a handful of other alkanes, plus additives including detergents, and possibly oxygenators such as MTBE (methyl tert-butyl ether) or ethanol/methanol. These compounds all alter the stoichiometric ratio, with most of the additives pushing the ratio downward (oxygenators bring extra oxygen to the combustion event in liquid form that is released at time of combustions; for MTBE-laden fuel, a stoichiometric ratio can be as low as 14.1:1). Vehicles using an oxygen sensor(s) or other feedback-loop to control fuel to air ratios (usually by controlling fuel volume) will usually compensate automatically for this change in the fuel's stoichiometric rate by measuring the exhaust gas composition, while vehicles without such controls (such as most motorcycles until recently, and cars predating the mid-1980s) may have difficulties running certain boutique blends of fuels (esp. winter fuels used in some areas) and may need to be rejetted (or otherwise have the fueling ratios altered) to compensate for special boutique fuel mixes. Vehicles using oxygen sensors enable the air-fuel ratio to be monitored by means of an air fuel ratio meter.

I like 12:1
 

Van Epps

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Wow... Thanks..

Ok..so I take it that the afr gauge measures the PRE combustion air / fuel ratio. I take it that if the correct ratio is known prior to running (we'll use 12.1) with the afr gauge we can very quickly know where the actual ratio is and make appropriate changes?

Question 2..does the info these provide tell where your ratio is in multiple rpm ranges (low, mid, top end) or just one reading?
If it only provides one reading how would you isolate the afr in each of these ranges.. simply do constant throttle position runs, one in each range?
 
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Mjunkie

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Wow... Thanks..

Ok..so I take it that the afr gauge measures the PRE combustion air / fuel ratio. I take it that if the correct ratio is known prior to running (we'll use 12.1) with the afr gauge we can very quickly know where the actual ratio is and make appropriate changes?

Question 2..does the info these provide tell where your ratio is in multiple rpm ranges (low, mid, top end) or just one reading?
If it only provides one reading how would you isolate the afr in each of these ranges.. simple do constant throttle position runs, one in each range?
It doesn't measure pre-combustion air/fuel. It is an oxygen sensor (basically) like cars have in their exhaust pipes. On a car, the o2 sensor in the pipe tells the computer how much oxygen is in the exhaust and then the computer can either add fuel or subtract fuel (and does so constantly) to adjust the mixture. In a 2-stroke application, the oil in the exhaust will over time damage the o2 sensor and ruin it completely, also in snowmobiles they obviously don't normally have an o2 sensor to relay oxygen levels to the ecu to automatically adjust the mixture, so adjustments must be made manually. The way I understand it in a sled is the o2 sensor will give you a ratio of oxygen to fuel and I'm assuming it will be relatively easy to see the ratio at a given rpm and immediately know if you are too rich or too lean or just about right. With efi, and a fuel control box, you can simply take the time to adjust all of the rpm levels to where they need to be for your given air temp, and altitude (because these will change needed mixture as well), and basically be done. EGT's give you a temperature reading, but this reading will vary depending on where the probe is located, and a "good" reading is hard to know since different motors will run differently. My dad has a cutler 1150 and was told by cutler to not let your egt's go above about 1100, on my motor I was told not to go much above 1200, I read on his 1300 kit that you shouldn't go above 1050. A "good" temp is also subject to change if timing has been changed. To me there are a lot of variables when the o2 sensor just tells you flat out where you're at.
 

Rick!

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I like using both EGT and AFR. My experience is that the Bosch WB O2 will last about 1000 miles before fouling and reading to the lean side. Replacements are like $70 so it's not like it costs a bunch to keep it maintained. Going off of Polaris late model stuff, 12.5 to 12.75 works real well at WOT on the flat. Seems they run leaner at altitude, like 13.5-15.5:1 with EGT around 1200-1250 in the center of the mid section of the pipe and sometimes a little higher. Sounds like your mod engine guys are leaving some hp on the table if you are only running 1050-1150 for EGTs.
 

4Z

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Sounds like your mod engine guys are leaving some hp on the table if you are only running 1050-1150 for EGTs.
Very true, but like Mjunkie said, it depends upon the motor and set up. I had a 1200 watercraft that loved 1300-1350. I even saw 1400 on climbs. I was riddled on that one until I had my engine guru explain to me why that is possible.
Same motor, different pipes and location of probes would only run a 1150.

I wouldn't blame Cutler for keeping things on the cool side, it would keep average customer happy and warranty claims down?

Running a motor in the sweet spot takes some responsibility on the owners part. It is not 100% pull-n-go all the time. But, once a person accepts the added care and feeding. Life can be very good IMHO.
 

Mjunkie

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First off Rick, even though I may or my dad may be getting only 1050-1150 EGT readings that doesn't necessarily mean there is more hp left to gain. If those are the readings we get but when we look at the piston wash and we're on the ragged edge of being too lean, are you trying to tell us we should go leaner to get those hp's "left" on the table? One "good" EGT reading on one motor doesn't mean it will be the same on every motor. That was the point I was trying to make before!!! For example my motor has 4 degrees of advanced timing over stock. That lowers my EGT reading because more heat is being absorbed by the piston because of a longer burn time before the exhaust port opens. That in turn means there is less heat in the exhaust. What about different probe placements? That will also change temp readings. It isn't rocket science when you think about it. THERE ARE TOO MANY VARIABLES TO COMPARE THEM APPLES TO APPLES!!! That is another reason why I think the o2 thing is better. I THINK it will be a more universal number from engine to engine. IMO there is still nothing out there that is more accurate for tuning a 2-stroke than reading piston wash, no matter what your EGT or o2 reads.
 
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LRD

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I like using both EGT and AFR. My experience is that the Bosch WB O2 will last about 1000 miles before fouling and reading to the lean side. Replacements are like $70 so it's not like it costs a bunch to keep it maintained. Going off of Polaris late model stuff, 12.5 to 12.75 works real well at WOT on the flat. Seems they run leaner at altitude, like 13.5-15.5:1 with EGT around 1200-1250 in the center of the mid section of the pipe and sometimes a little higher. Sounds like your mod engine guys are leaving some hp on the table if you are only running 1050-1150 for EGTs.
With mod motors EGT's can be deceiving, the higher the compression the lower the EGT temps. More heat is absorbed into the cooling system and more is converted into torque. Few years back I ported up three 670 cylinders for a 1050 heavy mod drag motor, EGT's were in the mid 1000 range but it dynoed solid 245 HP. Two of those cylinders would have been around 160 HP, very very healthy for a 670. Nothing left on the table.

Good Luck
 

fredw

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i gotta agree here

i also have a mod sled that runs around the 950 to 1070f temps, it has ran like that for tow years now, and runs very well, this last weekend, my self and another 860 that was running very well 1290f ran a few hills, back to back, on the last pull we checked plugs at the top of a long pull to compare, yes his plugs looked a bit leaner, maybe a few jet sises, but not more than a few, really do not think there is much power left on the table, and a safety zone with nitrous can come in handy sometimes



First off Rick, even though I may or my dad may be getting only 1050-1150 EGT readings that doesn't necessarily mean there is more hp left to gain. If those are the readings we get but when we look at the piston wash and we're on the ragged edge of being too lean, are you trying to tell us we should go leaner to get those hp's "left" on the table? One "good" EGT reading on one motor doesn't mean it will be the same on every motor. That was the point I was trying to make before!!! For example my motor has 4 degrees of advanced timing over stock. That lowers my EGT reading because more heat is being absorbed by the piston because of a longer burn time before the exhaust port opens. That in turn means there is less heat in the exhaust. What about different probe placements? That will also change temp readings. It isn't rocket science when you think about it. THERE ARE TOO MANY VARIABLES TO COMPARE THEM APPLES TO APPLES!!! That is another reason why I think the o2 thing is better. I THINK it will be a more universal number from engine to engine. IMO there is still nothing out there that is more accurate for tuning a 2-stroke than reading piston wash, no matter what your EGT or o2 reads.