Exhaust cutouts?

[88Racing]

Maybe this will help?
http://forum.gopowerhungry.com/lates...ss-3-15-a.html

[UNITY]

That would be cool! Thanks for the heads up!

[UNITY]

I am stuck on this again.. I am trying to figure out how to design the new exhaust so that I can have a tune with cats for on the road and a tune with out cats for off road.

My problem is where do I put the O2 sensors and do I do any thing to them?

It seems that if I have the cut outs before the cats that I should have the O2 sensors before them both right? If so, do I do that O2 sensor modification in the thread posted ^?

[88Racing]

Give me a couple of days to think about what your asking?

[Longshot270]

Bypass maybe? If it would fit you could weld a bypass with a similar machenism to the throttle body. With that closed the exhaust will be forced to go through the cat and o2 sensor. When it is open the majority of the gas will take the bypass because of it having the least amount of resistance. You would probably have to have 2 different tunes though. One for when the plate is closed and another when it is open because the second one will have to not only take care of the better flow but also the lack of your o2 sensor's input to adjust A/F ratios. You could also set up the bypass like some chevy exhaust that has the two pipes welded to 2 plates and the plates are bolted together. Just stick a piece of flat metal next to the seal to keep the exhaust from taking the bypass.

[UNITY]

Originally Posted by Longshot270

Bypass maybe? If it would fit you could weld a bypass with a similar machenism to the throttle body. With that closed the exhaust will be forced to go through the cat and o2 sensor. When it is open the majority of the gas will take the bypass because of it having the least amount of resistance. You would probably have to have 2 different tunes though. One for when the plate is closed and another when it is open because the second one will have to not only take care of the better flow but also the lack of your o2 sensor's input to adjust A/F ratios. You could also set up the bypass like some chevy exhaust that has the two pipes welded to 2 plates and the plates are bolted together. Just stick a piece of flat metal next to the seal to keep the exhaust from taking the bypass.

That is basically what I am going to try and do except my new question was what do I do with the O2 sensors. There will be 2 different tunes but you cant really tune one with O2 sensors and the other with out. Now what I am trying to figure out is if you relocate the O2 sensors before the exhaust cutouts will I need to modify the O2s or can I just leave them. 2 different exhaust set ups are not really a common thing for a tuner to have to tune for. At least 2 "quick" exhaust changes. Not just an "unbolt this one and put on a completely new one". I guess it really just depends on how sensitive the O2 sensors are and how effected they will be.

[Longshot270]

Originally Posted by UNITY

That is basically what I am going to try and do except my new question was what do I do with the O2 sensors. There will be 2 different tunes but you cant really tune one with O2 sensors and the other with out. Now what I am trying to figure out is if you relocate the O2 sensors before the exhaust cutouts will I need to modify the O2s or can I just leave them. 2 different exhaust set ups are not really a common thing for a tuner to have to tune for. At least 2 "quick" exhaust changes. Not just an "unbolt this one and put on a completely new one". I guess it really just depends on how sensitive the O2 sensors are and how effected they will be.

If he is making 2 different tunes, the first will be as if the truck had a regular exhaust system and the second would be if the truck was straight piped from the headers. If you straight pipe the exhaust the O2 sensor is going to go crazy anyway if you were to leave it in there. You could probably relocate the sensor to be after the bypass. Whenever you open or close the bypass you switch tunes.

[907DAVE]

Originally Posted by UNITY

My problem is where do I put the O2 sensors and do I do any thing to them?

It seems that if I have the cut outs before the cats that I should have the O2 sensors before them both right? If so, do I do that O2 sensor modification in the thread posted ^?

Yes, you must have your O2 sensors before your cutouts. I would place them around 8-12'' before the cutouts to eliminate any false reading caused by the negative exhaust pulses. Do not use the anti-fouler's on them either, they need to be in direct exhaust flow to be accurate and responsive.

As for the rear O2's, I would just leave them alone, no anti-fouler's.

Then all you would need is a "no cat" program designed to ignore the rear sensors to eliminate and P0420 codes, and a "cat" program that will watch the sensors.

Should be no sweat for Bill to handle.

[UNITY]

Originally Posted by 907dave

Yes, you must have your O2 sensors before your cutouts. I would place them around 8-12'' before the cutouts to eliminate any false reading caused by the negative exhaust pulses. Do not use the anti-fouler's on them either, they need to be in direct exhaust flow to be accurate and responsive.

As for the rear O2's, I would just leave them alone, no anti-fouler's.

Then all you would need is a "no cat" program designed to ignore the rear sensors to eliminate and P0420 codes, and a "cat" program that will watch the sensors.

Should be no sweat for Bill to handle.

That is what I was hoping for. So it is doable to "turn off" the rear O2 sensors? Was not sure how that worked on the OBD2 systems. That would be amazing! The power...the sound

[907DAVE]

Yeah buddy.........sounds like a cool project!

Regardless of what tuner you go with can you let us know how everything works out?