I've messed around a lot with different diameter and length exhaust pipes and mufflers on motorcycles and never had as good performance with a shorter than stock pipe (pipes)... After installing the KWSC 5PSI base kit I had been using a 2 1/2" axle back pipe with a 12" long glass pack muffler and switched to the stock muffler and pipe... The difference it made throughout the power band surprised the hell out of me and the top end speed was even 2 or 3 MPH higher... Lyons Night Road was messing around with an outlet pipe idea that was to exit before the B pipe using a electric solenoid to open it but I don't know what happened... He had also made up a turbocharger system from scratch.... I feel you will throw a number of codes by doing what you are suggesting.. There may be a power gain somewhere in the lower mid range of the power band but very little.. There will also be a loss of power early on at low revs and from the upper mid range on up... I have a tweaked exhaust system and it wouldn't work well at all on an engine that wasn't boosted.. I have an exhaust control valve to close of the pipe in front of the rear resonator and AeroTurbine muffler... The down pipe the replaces the cat also has a resonator and the B pipe has one that is larger than the stock one... Between 60 MPH and 80 MPH it is painful to sit in with out ear plugs, but from 85 on up or 55 and below it is okay unless the throttle pedal is down... A short pipe isn't going to scavenge and allow enough intake flow during the transition when the intake valve opens before the exhaust cycle is complete and the exhaust valve is completely closed.

 

Here is the stock converter next to the J's downpipe I am running. As you can see on the stock pipe, the sensor is before the actual converter. So going with a downpipe will not fail an OBD-II check, but it might possibly fail on a sniffer check.

 

Did you have to do any kind of trick fix on the J's pipe like using a couple of spark plug defoulers?? Your stock cat pipe looks very much like a Megan down pipe with a resonator.... I pass inspection with one.

 

TC that's the thing, no need to as the secondary sensor comes before the actual converter. The secondary sensor is reading from the primary converter. The secondary converter plays no part in the OBD-II and is just there to further clean up the exhaust and possibly for visual inspections as it is not very easy to see the primary close-coupled converter hanging off the block.

 

If you're just looking to save weight why not just run a straight pipe out the back?

If you're going to put a 90 degree bend in the pipe to run it out the side that's kind of counter-productive...