merge collector on headers

[Boiler Ben]

I am building a street FE engine for a Cobra.  My Cobra kit came with SS long tube headers and I need to find a way to put an oxygen sensor on one side.  I've found some pieces meant for this and a shop that could probably do it.  My question is about how the engine would react to having this merge collector only on one side.  I'd prefer not to modify both.  The exhaust flow pattern would be different on each side but maybe not enough to notice?

[cjshaker]

Your post is a little confusing. Are these side pipes like you see on many Cobras? If so, I'd think a simple bung welded on the backside on one of the side pipes, after they merge, should work and not be visible. If it's a regular 'out the back' exhaust, each header already has a merge collector, so are you talking about an extension for the O2 sensor bung? An extension shouldn't be anything more than a piece of pipe; no different than the rest of the exhaust system, so shouldn't affect anything. If they're slip-on collectors, you may not get an accurate O2 reading. They're very sensitive to leaks, which would throw off the reading.

[Boiler Ben]

The side pipes look like the pic.  The headers are separate all the way to the flange, then remain separate until they go into the muffler section.  There is 1-2 inches where a sensor port could fit on the side pipes, but that is on the outside of the car and either pointed down and in or up and into the footbox area.  So my thought was to modify the headers 4 into 1 and back into 4.  But only do that on one side.

[pbf777]

So my thought was to modify the headers 4 into 1 and back into 4.  But only do that on one side.

       Boy . . . . . I'd have to pass on that idea.     That is if this were any kind of performance related intention. and where the headers 'were' suppose to provide any function toward that end. 

       One problem you'll probably suffer is that the O2 sensors are intended to be close enough to the exhaust exit of the cylinder to be heated, too far down line (or even possibly just "sticking out in the wind"  ) and they're running too cold and won't necessarily provide an accurate reading value; and even if so, then they might not be getting hot enough to cook-off the by-products of combustion that will likely tend to adhere to them, this also causing inaccurate values and a shorter useful service life span. 

       Is this need for an O2 sensor because your adopting an "E.F.I." system?  Or just for the purpose of utilizing a "lean-rich"/"air-fuel ratio" instrument?    Particularly if the latter, all I can say is:  It ain't worth it!  Better to just "read the plugs". 

       And then, as previously mentioned, the exhaust must be "sealed-up", no leaks; but even then, with the side pipes presenting a rather short distance length from the proposed O2 sensor and the open atmosphere, if with a sum of camshaft overlap, or any other reason causing significant reversion in the pipes, the functionality in the sensors is lost!   

       Scott.

[Barry_R]

You're over thinking it.  Just put the sensor in an inch or two forward of the point where it goes into the single tube/muffler area.  Get it as high as you can before hitting the footbox etc - just don't point it down to the ground (lowest spot would be vulnerable to removal by speed bumps...).  All the instruction want them "up to avoid moisture contamination and for longevity - but you really don't care if you need to buy another one in 30,000 miles.  If you're running EFI with it you obviously need it always installed.  But if it's for data gathering, you can put the bung pointing outside the car and plug it during normal use after tuning.  I have seem OEM test cars running around Detroit with tons of wires and boxes flapping around in the breeze...  No real car guy is ever going to object to the visuals of an O2 bung/plug - it gives you something to talk about for those that don't understand.

[My427stang]

Barry nailed it, find a spot and point it up toward the footbox, aim up as close as you can to 10:00 / 2:00 as you can. and make sure you give a little room for engine rock.  Nobody will likely even see it with a Cobra sitting low. 

As far as location, I like to see the location a bit farther back from the primary pipes, not sure if it matters, but the O2 can either see mostly one cylinder's output or a blend of the 4 on that bank.  I wouldn't go to the rear bumper, but all modern EFI kits use a heated sensor, not a big deal.   I shoot for a little bit further away, (think rear of collector or even in the front of an H-pipe on a traditional exhaust)  and depending on the EFI system you use, there may be an adjustment to O2 delay that corresponds to how far from the exhaust port it is, not all have those, but it allows a little offset if very close or very far away.  That calculation is generally done by measuring and using the EFI kit recommendation.