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Old 01-22-2015, 11:01 PM   #1
brianwheelies OP
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EFI with O2 sensor w/aftermarket exhaust

If my bike is EFI with an O2 sensor, will adding a full exhaust and reusable high flow filter cause running issues?

TIA
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Old 01-23-2015, 07:15 AM   #2
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Originally Posted by brianwheelies View Post
If my bike is EFI with an O2 sensor, will adding a full exhaust and reusable high flow filter cause running issues?

TIA

does the new exhaust have sensor bungs? I would imagine most efi bikes are on the lean side and should be programmed after a change like that. The filter probably won't make a bit of difference.
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Old 01-23-2015, 07:19 AM   #3
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o2 sensor is usually for closed-loop operation, meaning, the ecu will adjust/trim fuel based on o2 output, to re-match programmed condition.

what bike? are you eliminating the o2 sensor completely?
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Old 01-23-2015, 07:34 AM   #4
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Yamaha Smax 155cc. New exhaust has the O2 bung. This will drop a lot of weight and remove the cat.
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Old 01-23-2015, 07:38 AM   #5
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Yamaha Smax 155cc. New exhaust has the O2 bung. This will drop a lot of weight and remove the cat.
If you're removing the cat I would get it remapped.
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Old 01-23-2015, 11:52 AM   #6
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Don't automatically assume that it's running lean from the factory. There are lots of bikes and even many cars that run leanish in normal engine speeds/ load positions but turn pig rich with load or rpm. The only way to truly know is to test it with an O2. IMO, just putting a slip on muffler is probably not going to be damaging.
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Old 01-23-2015, 11:57 AM   #7
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Don't automatically assume that it's running lean from the factory. There are lots of bikes and even many cars that run leanish in normal engine speeds/ load positions but turn pig rich with load or rpm. The only way to truly know is to test it with an O2. IMO, just putting a slip on muffler is probably not going to be damaging.

you're correct, but he said full exhaust without a cat, not just a slip on.
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Old 01-23-2015, 01:05 PM   #8
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If the O2 sensor is before the cat, then the bike won't know if the cat is missing or not.
After the cat, then you run into problems, as it's checking for the existents of the cat and how well it's operating. But I have not seen many bike with that system. Mostly BMWs.

Now adding a free flow exhaust system may increase the air flow enough to cause it to run lean. If you leave the pre-cat O2 sensor in, the ECU will attempt to compensate for the exhaust at idle and cruising. Maybe it can do it, maybe not.

At WOT, all EFI systems ignore the O2 sensors and dump fuel into the motor. My pickup gets down in the 11:1 ratio at WOT when cold.
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Old 01-23-2015, 01:08 PM   #9
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O2 sensor is just outside of the exhaust port and has a ways to go until reaching the cat'ed muffler.

It is a full exhaust system

The bike is so new that there are few to no parts available stateside.
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Old 01-23-2015, 01:36 PM   #10
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Originally Posted by brianwheelies View Post
If my bike is EFI with an O2 sensor, will adding a full exhaust and reusable high flow filter cause running issues?

TIA
Ask the lean minded people to explain "lean" bet they don't even know what lean is.
14.7 is stoichiometric you can drop below that by a few points (a narrowband O2 will cycle between 13.6 rich and 15.3 lean which is normal) and still be fine. I run my truck at cruise @16.1 for fuel savings, have read of 17.2 @cruise, no load. If to lean it will pop on throttle, and believe it or not but to rich will rob more power than to lean.
I have a FZ6R and CAT is removed and reusable filter with no Power Commander or any other injector pulse width modulator adjustments (what most add-on boxes do), and no problems, checked with remote wideband sensor (more precise than a narrowband O2, used to dial in correct AFR) and was still 10.3 at idle [rich] (no O2)
I tune GM products for a living, while a automotive PCM, ECU is more complicated than the little motorcycle ones they work much the same, all PCMs, ECUs have a window of adjustments, meaning small changes such as air filter, open exhaust are perfectly fine and the PCM ECU will adjust to them (narrowband O2 in exhaust will adjust easily all it does is keep stoich at idle and cruise), now adding a larger profile cam, boost in the way of a turbocharger, that changes the game some and will need tuning for that.
In the old days when you would do an exhaust and air filter the old carburetors would need some rejetting so I guess most people assume and wrongly so, so does a EFI system. Just remember this -- an engine unless something changes it drastically is still the same engine, you have to add hard parts to make an engine a lot more powerful, tuning can't do it. There is a lot more but you get the gist of it.

Hoaruptop screwed with this post 01-23-2015 at 01:47 PM
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Old 01-23-2015, 03:57 PM   #11
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Originally Posted by brianwheelies View Post
O2 sensor is just outside of the exhaust port and has a ways to go until reaching the cat'ed muffler.

It is a full exhaust system

The bike is so new that there are few to no parts available stateside.
If there's no O2 sensor aft of the cat on the stock exhaust there shouldn't be any problem.

The single O2 sensor just outside the exhaust port tells the ecu how rich or lean the engine is running. This input, along with inputs from temperature and throttle position sensors are used by the ecu to regulate injector duration to achieve ideal engine performance, lowest possible emissions and best fuel economy. This "closed loop" mode is usually bypassed below normal operating temperatures and when running WOT. Systems with a second sensor aft of the catalyst use that second sensor solely to monitor the the effectiveness of the cat, illuminating the MIL (Malfunction Indicator Lamp) if the converter efficiency drops out of spec.

Most systems have enough leeway in injector duration to compensate for the somewhat more free flowing exhaust. I would not expect any significant improvement in power from the new exhaust, but if all you want is lighter weight or a different sound or look then go for it.
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Old 01-23-2015, 04:50 PM   #12
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Normal cruise it should be fine. O2 closed loop correction.
Under load I don't know if that bike will stay in closed loop. Many times it will default to an open loop pre-programmed mapping. Full throttle closed loop tuning is fairly new in the car world (past 10 years or so it started to occur). I strongly suspect that the bike will go open loop under load. I would at least have it tested and tuned if needed. But a gentle ride to get it checked will be fine.
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Old 01-23-2015, 05:23 PM   #13
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The jury is still out on the exhaust. I would be going with a brand I am not familiar with for the experiment(Over Racing or Beams) as nobody has gotten much tuning info since the bike is so new.

I do thank you guys for your input.
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Old 01-23-2015, 05:56 PM   #14
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I run my truck at cruise @16.1 for fuel savings, have read of 17.2 @cruise, no load.
You may want to reconsider running at ~16 AFRs... It's been a while since i've been in the tuning game, but IIRC, ratios around 16.1-16.2 typically produce the highest egts... in the burning valve temp range!! (Unless you're running Ti valves)
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Old 01-23-2015, 08:04 PM   #15
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I also run between 16:1 and 17:1 at cruise (as shown by the little meter that goes beep) wherever possible.

Including on my old ACVW Beetle, everyone knows they never get hot or overheat exhaust valves.
My last one tuned the same way for cruise stayed lucky for 200000km............
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