Aftermarket Headers

[dyeager535]

I need to get one of those for when I do my exhaust system. I want to install it into the Y-pipe, so the O2 sensor will read both sides of the exhaust system. There is a possibility I may have to move the Y-pipe back further away from the headers than the stock position, and it will need a 3-wire heated O2 sensor.

I'd rather have a bung in both pipes, and if I was having a problem be able to swap O2 from one to the other, if I was going to worry about it. But since you can pull a plug wire and do the same thing, I wouldn't second guess GM too much on it.

Since one injector does not feed one side of the engine, unless you have a mechanical problem on one side of the engine, an O2 sensor mounted in one bank, upstream, will be fine. A bad valve, plug, whatever would get some help with diagnosis (potentially) when both banks are monitored, but you'd know there was a problem without needing the O2 sensor to tell you. IMO.

I suspect GM went the way they did with mounting the O2, because a problem is more likely to be electronic than mechanical, thus it doesn't matter so much whether all 8 cylinders are monitored or 4.

FWIW, in stock tune, my O2 sensor mounted 3+ feet from the cylinder head (past the header collector) would go open loop only at idle, and the instant I touched the throttle, would close. It ran absolutely no different with a heated O2. I got lazy with my open loop tune and simply changed it to go closed loop almost instantly after start, which the heated O2 helped with. I'm guessing GM went heated for a different reason, but with the same method...clean up startup/cold engine emissions by going closed loop faster.

 

[1-ton]

I'd rather have a bung in both pipes, and if I was having a problem be able to swap O2 from one to the other, if I was going to worry about it. But since you can pull a plug wire and do the same thing, I wouldn't second guess GM too much on it.

Since one injector does not feed one side of the engine, unless you have a mechanical problem on one side of the engine, an O2 sensor mounted in one bank, upstream, will be fine. A bad valve, plug, whatever would get some help with diagnosis (potentially) when both banks are monitored, but you'd know there was a problem without needing the O2 sensor to tell you. IMO.

I suspect GM went the way they did with mounting the O2, because a problem is more likely to be electronic than mechanical, thus it doesn't matter so much whether all 8 cylinders are monitored or 4.

FWIW, in stock tune, my O2 sensor mounted 3+ feet from the cylinder head (past the header collector) would go open loop only at idle, and the instant I touched the throttle, would close. It ran absolutely no different with a heated O2. I got lazy with my open loop tune and simply changed it to go closed loop almost instantly after start, which the heated O2 helped with. I'm guessing GM went heated for a different reason, but with the same method...clean up startup/cold engine emissions by going closed loop faster.

I would have to agree. If one bank cylinders can not get it right, then the engine has more problems than O2 precise placement can cure.

 

[1-ton]

I was at an exhaust shop the other day, and there was an old square body Chevy there that was had a set of Flowtech PN# 11508 headers on it. I am glad I got to see how those headers fit before I installed mine. The Left side is collector flange is very very close to the frame, and the Right side is very very close to the trans bell housing. Other than that they seem to fit just fine. After I got a look at this truck, I told the guy at the muffler shop that I had the same headers as the ones he was working on. He suggested cutting off the header collector flanges, and going with a V-Clamp set up instead, in order to get more clearance.

 

[dyeager535]

I looked at those clamps, but they are fairly pricey and look to be a bit of a bear to install under less than ideal working conditions. But I think they'd work better than any other "removable" exhaust clamp I've seen so far.

Eventually I plan to use a section of flex pipe to further isolate the headers/engine side of the exhaust, and the rear portion of the exhaust. Hasn't been too much of a problem, but I also weld the collector nuts to the bolts as habit. While the exhaust is pretty solid, I'd rather do everything possible to keep from working the header to head flange, and collector bolts. Doing a very good job of making sure the collector mateup is square would also probably help, but I think that is one reason GM used the springs on the exhaust bolts...the y-pipe seems to "grow" as it heats a bit, in addition to being able to better soak up some of the movement of the frame/exhaust hangers in relation to the engine.