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2008 YZF-R125 (180cc)
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Most likely not an issue since it will certainly have an O2 sensor so however the breathign characteristics change it ought to just adapt back to stoichometric/14.4:1
 

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Super Moderator
2008 YZF-R125 (180cc)
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a Narrowband O2 (NBO2) sensor only really knows 3 states, lean, stoich and rich. This is the type of sensor fitted to almost all modern vehicles, cars as well as bikes. For the vast majority of cases this is fine since most people aren't that conccerned with performance so stoich (14.4:1) is a reasonable balance between power and efficiency. However the ECU expects a reading from the NB02 so if you change the breathing characteristics of your bike (e.g. exhaust, intake tuning), then whilst tthere will be better airflow and accordingly potential for better performance, the ecu will be like "huh, ok" and just adjust till it gets back to stoich. Better, but still not optimal. So you would prob see an improvement but not as much of an improvement as it could be if it was mapped for power, which is more like 12.6-13 AFR (lower is richer)

Slope Rectangle Font Line Parallel


A wideband will give you a full range of readings from very rich (e.g. 8 AFR) up tto very lean (e.g. 20+) so lets you map for (e.g.) power or efficiency or whatever in between, and that's where you see quite a lot of improvement, not just intop speed but overall response throughout the range.

Unfrotunately you can't just whack a wideband in place of the NBO2 since they work a bit differently and ECU expects the input from the NB02 and will throw a wobbly if you mess with the fuelling (e.g. by trying to fit a piggyback fuel controller like a PCV) - Search on here - there's a thread by Hildero who tried to tune his Gen2 this way and every time the workshop adjusted the fuelling to be richer the ECU was like "nah bruv" and adjusted it back.

Some aftermarket fuelling systems (e.g. Rapidbikes EVO/Race) do a thing where they send a fake NBO2 signal to the ECU so it doesn't freak out and throw a code, but then take the real input from a wideband and then you can tune how you like. I would have thought something like this would be the best option to tune a modern bike, though my newest bike is a gen1 so doesn't have an O2 sensor as stock, so adding one + wideband + autotune module works, whereas you just can't do that on a gen2+.

There is actually a tiny bit of room for "hacking" an NBO2 sensor since there is a very small part of the range where it'll read a little bit either side of stoich, and you can quite easily make a little device which sits inline with the NBO2 sensor and makes it read everso slightly (e.g. 0.01-0.02volts) under (lean), andthat fools the ecu into thinking it's running a bit below stoich and hey better send a bit more fuel so we're good, the net result being a bit richer. It's never gonna be as good as a proper remap + wideband but it'll let you squeeze a bit more power out of it and it's extremely cheap and easy to do. The device just goes inline with the O2 sensor.

Below is a graph showing voltage vs AFR for a NBO2. See the bit in the middle where the lines meet up... as far as I understand it that's basically the area where it works. It's not much but it's something, and would apply universally across the range/map.. so it would be "a little richer" across the whole range.. which may or may not be a good thing. You might find it idles a bit rougher or bogs a little on takeoff but maybe that's worth putting up with because it's more fun when you're giving it some.

(Image taken from the url at the bottom)
Rectangle Slope Font Parallel Pattern


I built such a device for someone on a lexmoto which had zero tuning options, but then they dropped off the map so I never got to test it and I don't have a vehicle with an NBO2 myself so it's just sitting in my electronics project box. It's based on this person's work (url below), and seems to be something harley owners do, but there's a trademark on it which means they don't print specifics/values of the components involved and also commercial production of such a device would be a trademark infringement (because yay capitalism) - otherwise I would be selling them haha. It is however based on a very simple principle of a voltage divider which is easily googleable and the values for the components are not difficult to fathom with a bit of testign and a multimeter. The one i built had a little potentiometer so you could dial in the amount of "fudge value" and it was actually surprisingly accurate.

Whilst I don't have an NBO2-equipped vehicle I do have a NBO2 sensor for testing stuff and I was able to use the device to demonstrate adjusting the readings quite accurately (by ~0.01v) so as far as I could tell without having an NBO2-equipped vehicle - it seemed to work (plus the harley boys do it so it's def not rocket science ;) ).

(Unlisted) video of me demoing the proof-of-concept circuit here which I then later wrapped up into a PCB in a sealed box:

based on the work of Knight rider here (who i think holds the patent):
 

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Discussion Starter · #5 ·
a Narrowband O2 (NBO2) sensor only really knows 3 states, lean, stoich and rich. This is the type of sensor fitted to almost all modern vehicles, cars as well as bikes. For the vast majority of cases this is fine since most people aren't that conccerned with performance so stoich (14.4:1) is a reasonable balance between power and efficiency. However the ECU expects a reading from the NB02 so if you change the breathing characteristics of your bike (e.g. exhaust, intake tuning), then whilst tthere will be better airflow and accordingly potential for better performance, the ecu will be like "huh, ok" and just adjust till it gets back to stoich. Better, but still not optimal. So you would prob see an improvement but not as much of an improvement as it could be if it was mapped for power, which is more like 12.6-13 AFR (lower is richer)

View attachment 34168

A wideband will give you a full range of readings from very rich (e.g. 8 AFR) up tto very lean (e.g. 20+) so lets you map for (e.g.) power or efficiency or whatever in between, and that's where you see quite a lot of improvement, not just intop speed but overall response throughout the range.

Unfrotunately you can't just whack a wideband in place of the NBO2 since they work a bit differently and ECU expects the input from the NB02 and will throw a wobbly if you mess with the fuelling (e.g. by trying to fit a piggyback fuel controller like a PCV) - Search on here - there's a thread by Hildero who tried to tune his Gen2 this way and every time the workshop adjusted the fuelling to be richer the ECU was like "nah bruv" and adjusted it back.

Some aftermarket fuelling systems (e.g. Rapidbikes EVO/Race) do a thing where they send a fake NBO2 signal to the ECU so it doesn't freak out and throw a code, but then take the real input from a wideband and then you can tune how you like. I would have thought something like this would be the best option to tune a modern bike, though my newest bike is a gen1 so doesn't have an O2 sensor as stock, so adding one + wideband + autotune module works, whereas you just can't do that on a gen2+.

There is actually a tiny bit of room for "hacking" an NBO2 sensor since there is a very small part of the range where it'll read a little bit either side of stoich, and you can quite easily make a little device which sits inline with the NBO2 sensor and makes it read everso slightly (e.g. 0.01-0.02volts) under (lean), andthat fools the ecu into thinking it's running a bit below stoich and hey better send a bit more fuel so we're good, the net result being a bit richer. It's never gonna be as good as a proper remap + wideband but it'll let you squeeze a bit more power out of it and it's extremely cheap and easy to do. The device just goes inline with the O2 sensor.

Below is a graph showing voltage vs AFR for a NBO2. See the bit in the middle where the lines meet up... as far as I understand it that's basically the area where it works. It's not much but it's something, and would apply universally across the range/map.. so it would be "a little richer" across the whole range.. which may or may not be a good thing. You might find it idles a bit rougher or bogs a little on takeoff but maybe that's worth putting up with because it's more fun when you're giving it some.

(Image taken from the url at the bottom)
View attachment 34169

I built such a device for someone on a lexmoto which had zero tuning options, but then they dropped off the map so I never got to test it and I don't have a vehicle with an NBO2 myself so it's just sitting in my electronics project box. It's based on this person's work (url below), and seems to be something harley owners do, but there's a trademark on it which means they don't print specifics/values of the components involved and also commercial production of such a device would be a trademark infringement (because yay capitalism) - otherwise I would be selling them haha. It is however based on a very simple principle of a voltage divider which is easily googleable and the values for the components are not difficult to fathom with a bit of testign and a multimeter. The one i built had a little potentiometer so you could dial in the amount of "fudge value" and it was actually surprisingly accurate.

Whilst I don't have an NBO2-equipped vehicle I do have a NBO2 sensor for testing stuff and I was able to use the device to demonstrate adjusting the readings quite accurately (by ~0.01v) so as far as I could tell without having an NBO2-equipped vehicle - it seemed to work (plus the harley boys do it so it's def not rocket science ;) ).

(Unlisted) video of me demoing the proof-of-concept circuit here which I then later wrapped up into a PCB in a sealed box:

based on the work of Knight rider here (who i think holds the patent):
Good Lord that was a lot of information. Credit to you sir !

So long story short, the exhaust and filter will require a tune for maximum gains. But without the tune, the bike will still run perfectly fine without risking any long term damage ?
 

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Super Moderator
2008 YZF-R125 (180cc)
Joined
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707 Posts
no worries :) It's a subject I've been digging into for a while (clearly lol)

> So long story short, the exhaust and filter will require a tune for maximum gains. But without the tune, the bike will still run perfectly fine without risking any long term damage ?
exactly. Tbh I write the full explanation not just for you but for whoever googles it in future and ends up on this page and so that the next person who asks it can just be referred here. It's taken a LOT of time and effort to piece this info together and test it etc over the last couple of years since presumably mechanics don't really wanna tell folks too much bc it's their income and there's a lot of just garbage/misinformation info out there too.
 
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