That dosen't make sence. The point of the 02 sensor is to show the engine what the air/fuel mixture coming out the exhaust is and have the engine adjust to keep it correct. It reads the gas before the cat interacts with it. Removing the cat would be like putting on a slip on exhaust, it hardly changes the flow at all and not enough to change the mixture. Heck a full slip on not only removes the cat but also reduces backpressure from the muffler itself and you still don't need to re-map.

 

You should always re-map with a slip on... with loss of backpressure, you can toast valves. it makes perfect sense. the O2 sensors sometimes tell the motor to compensate for the higher flow of air, sometimes flooding the motor, and running rich. what doesn't make sense?

 

What dosen't make sence is the o2 sensor dosen't measure the volume of air going past it, only the oxygen content of the air. Besides that you aren't moving an extra volume of air with exhaust mods. The engine can only take in and fill the cylinders with X volume of air. Exhaust mods help with power because the engine dosen't have to push as hard to expell X volume of air, they don't change X.
As for toasting the valves, that has nothing to do with backpressure. You could run strait headers and not burn the valves. Backpressure just makes up for poor exhaust scavenging in a poorly designed system which is why some people equate backpressure to low end torque. Yes its always a good idea to re-map with mods but its been well proven that the F4i does not need it with just a slip on.

 

maybe I can clear this up....

your o2 and cat. Work like this...

your cat chanes your air to fuel ratio making your bike run at a normal level

after flowing through ur cat it hits the o2 sensor which detects the air/fuel ratio...

when you remove the cat. It no longer can regulate the a/f ratio so the o2 sensor picks up more air flowing in the exhaust mixture than noral and boosts up ur fuel flow this creating a bike that runs richer than it should....

a common symptom of this is fouling plugs

 

In a car kinda, but in a F4i the 02 sensor is before the cat, not after. The sensor has no idea what the cat is doing.

Normally with cars you have one o2 sensor before the cat to tell the computer how the engine is running and how to adjust for optimum engine performance. The second o2 which is behind the cat tells the computer when the cat has warmed up to operatiing temp along with if the cat is doing its job correctly. The 2nd o2 normally does not have an influence on engine metering.

If you can change the exhaust to both reduce backpressure and improve scanvenging you can create a natural ram air situation in the engine which will increase cylinder filling and therefore exhaust volume. That will affect the a/f but its not going to happen with the stock header and length restrictions of the exhaust [among other things] which is why I didn't point it out in my last post.

 

Advice has been bril so far guys! think i'll start shopping for an after market system then!

Thanks guys!

 

Not sure if this will help clear things up but I had an '01 f4i ; no o2 sensor or cat converter. Traded that in on an '06 f4i and it has both o2 sensor and cat converter. Stock exhaust system on both bikes.

 

get you a ecm off a early 49 states bike and eliminate the 02 sensor all together. I have to disagree that there wont be any difference. the 02 sensor is a narrowband and there will be a slight difference in how much o2 passes that sensor due to the restrictions in that cat. remove it and its going to change. now you could get a cali ecm and one of those non cat pipes and it should be mapped right, but id bet you that the ones with the cats have different maps. otherwise just get a pc3 and tune it however you want it. Could even buy a Innovate LC1 off ebay and tune for AFR.