Wideband and A/F bung location on X-pipe

elite130 · Apr 7, 2006

I was talking to a local speed/dyno shop near where I live about dyno runs w/ air/fuel ratio, they told me that the only way to get an accurate air/fuel reading was to install a threaded bung for a sensor before the cats. So, with that in mind...say I were to get a Magnaflow Catted X-pipe...before I were to install it, I want to get this threaded bung put on for future use. What is the best location for this sensor (driver or passenger side, before/after the X-over, just in front of a cat, or somewhere just after the exhaust manifold...)???

Also, what size should the hole/bung be?

Thanks for the help :SNSign:

myponyrocks · Apr 7, 2006

IMO the tail pipe sensor is good enough. Unless you're running a power adder then you may want the added protection of the most accurate A/F.

Mike97gt · Apr 7, 2006

if you have cats mount it before the cats it's recomended to keep them within 30" of the exhaust ports

personally I recomend to mount it just after one of the front 02 sensors ( the ones closest to the manifolds. it does not matter what side it's mounted on

myponyrocks said:
IMO the tail pipe sensor is good enough. Unless you're running a power adder then you may want the added protection of the most accurate A/F.

he has cats so the reading from the tail pipe sensor is inacurate.

Kilgore Trout · Apr 7, 2006

^^ did not know that...

myponyrocks · Apr 8, 2006

svttech76 said:
he has cats so the reading from the tail pipe sensor is inacurate.

Interesting... Are you a tuner? Here's what one of our local tuners told him

Mile High Dyno said:
Driver side, anywhere before the cats and you'll be fine......

I would agree, that using the bung is the most accurate way, but by no means is it a neccesity. If you keep up on the maintenance of a tailpipe sniffer they can be and are very accurate. I have tuned MANY 500+ hp cars on our dyno through the tailpipe with very little problems. Hell, I dont even have a bung in my car. A tailpipe sniffer always reads a little leaner than a bung would, so if you are safe through the tailpipe, you are really safe.

Take it for what it's worth......

DBMSTNG · Apr 8, 2006

i would use a O2 sensor at the tailpipe as reference only.

as for the location of a wideband O2 sensor on the mid-pipe, there is a nice opening on the drivers side near the header/mid-pipe connection before the exhaust bends under the car. that's where i added my bung and i haven't had any problems.

myponyrocks · Apr 8, 2006

Heres more info, from a widely known trustable source....

http://www.modularpowerhouse.com/forums/showthread.php?t=1767&highlight=dyno+bung+sniffer

The following is a qoute from the thread.

My original hypothesis was correct (I do have a degree related to this kind of thing, you know) - at low rpm, the tailpipe sniffer would be inaccurate (show lean) because of the lack of a sufficient exhaust gas flow. Large diameter exhaust pipes on small bore engines would be most susceptible to this problem. The exhaust flow would not be strong enough to displace all of the atmoshperic air. The graph proves this, as the reading below 3K is leaner than it should be. Once the engine flows enough gas, the tailpipe sniffer matches the pre-cat O2 sensor to within the normal variation found during most multi-run tests.

I thought there would be more of a time delay from the sniffer - maybe the Dynojet software takes that into account. Anyway, this should be useful information and save a lot of people from a lot of work (and worrying.)

Mike97gt · Apr 8, 2006

myponyrocks said:
Interesting... Are you a tuner? Here's what one of our local tuners told him

I don't own a dyno but I have tuned several cars.

having cats and sensing after them messes with readings, it's not much, but if your going to run a wideband setup and have cats you should put them before the cats, so you get a more accurate reading.

when tuning a friends z28 we used a pre cat wideband and the tail pipe sniffer and on his car the tailpipe sensor was reading a little lean and caused me to richen the mixture to much.

again the difference is very small and for 99 percent of the time it would not be a problem, but in this case I had to do some part throttle ajustments too and as your article stated at low rpm's the readings were off.

I still see some wide seperation at somepoints in that graph in the link you posted, at low rpm's and again at around 5500

myponyrocks · Apr 9, 2006

For a wide-band system I agree, but he was asking for a dyno. I don't think he's getting a wide band commander, he just made the thread wrong, but I could be wrong.... I'm good at it

elite130 · Apr 9, 2006

myponyrocks said:
For a wide-band system I agree, but he was asking for a dyno. I don't think he's getting a wide band commander, he just made the thread wrong, but I could be wrong.... I'm good at it

You are right and wrong...I'm not sure what the future will bring in regards to power adders, except I know I will probably get one one day. The main purpose of this thread was to find out best location for a bung on a catted x-pipe. I figure if I am getting the x-pipe, why not put the bung in while I have the x-pipe off the car, rather than dealing with it later when I am trying to get accurate A/F readings when doing a dyno pull or tuning the car. I guess it is all about future planning.

goshia · Apr 9, 2006

Does not matter what side you place the bung just make sure its in front of the CAT's. Are you doing your Dyno at Mathews? If so I would love to drop by and see your run.

myponyrocks · Apr 9, 2006

elite130 said:
I guess it is all about future planning.

I suck at that, I change parts left and right, I could have bought a S/C with all the money I've lost E-Baying parts

jstreet0204 · Apr 9, 2006

I does matter what side. The drivers side will tend to run leaner because it runs hotter. Place the bung before the cat on the drivers side.

Mike97gt · Apr 9, 2006

jstreet0204 said:
I does matter what side. The drivers side will tend to run leaner because it runs hotter. Place the bung before the cat on the drivers side.

yep the two back cylinders on the drivers side run hot.

elite130 · Apr 9, 2006

jstreet0204 said:
I does matter what side. The drivers side will tend to run leaner because it runs hotter. Place the bung before the cat on the drivers side.

Really??? I didn't know that. That is good info.

goshia said:
Are you doing your Dyno at Mathews? If so I would love to drop by and see your run.

I probably won't be running at Mathews since I just ran there March 4th..but our Mustang club will be having a dyno day up there May 15th. You should check it out. PM me if you want more info about our club and/or the event.

propellerhead · Apr 9, 2006

The forums at Innovate has some good info on sensor locations.

Wideband and A/F bung location on X-pipe

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