BritishV8 Forum

I am about to send my RV8 thru-the-wing headers for my MG off to be coated, but I want to weld a bung onto each of them for an O2 sensor first.

The all-knowing internet suggests that ideal placement is approximately 1m from the exhaust ports, and in a vertical or near-vertical position to avoid condensation drips.  I can't see how to do that on an LBC.  I see a few examples here where a sensor is just below the 4-to-1 collector, horizontally mounted, in the fender well before the header turns to the rear.  I'm wondering if a better spot is after the header turns horizontal, near the trans bellhousing?

Does anyone have some thoughts on where the best placement for 02 sensors should be, and hopefully a pic or two?

Many thanks,

Dave

What type of FI are you running? If Rover 14CUX follow the MG RV8 location which is after pipe turns horizontal.
If this is just an AFR gauge then it's less critical, mine is a single at the Y and function well.

IF using a wide band O2 with heater, it is not critical.  After the collector is fine with the bung pointing up.

I always put the bung on the side of the pipe so the sensor can be changed and that's the way the OEM's do it too. Under the car seems just fine. If you get up in the wheelwell with it you have to watch your tire clearance very carefully. The only way I could see condensation being a problem would be if you put it on the bottom of the pipe and then you'd be knocking it off on speed bumps.

Jim

Many thanks!  

I'll be running megasquirt FI with wideband sensors.  Looks like I'll go with a side mount on the horizontal portion of the header, after it exits the wheel well.  

Dave

QuoteI always put the bung on the side of the pipe so the sensor can be changed and that's the way the OEM's do it too.

Most probably do, but I found some that are up.

https://cdn4.pelicanparts.com/BMW/techarticles/BMW-3-Series-E46/26-FUEL-Oxygen_Sensor_Replacement/images_large/pic02.jpg

More info:

https://wbo2.com/lsu/position.htm

If you read the gauge manufacturer instructions you will find that they need to be at least 10deg inclined to prevent condensation fouling etc. Not too hard to do in a B. I have 3 sensors in.my car and all are on an angle.
Here is AEM's instructions.

http://aemelectronics.com/files/instructions/30-5130%20Analog%20Wideband%20UEGO%20Gauge%20Gasoline%20AFR.pdf

My second link says the same.

Ok, so here's my random ramblings on O2 sensors.
In general O2 sensors should be as close to the engine as possible.
This has nothing to do with response time and everything to do with heat.
Single wire (non heated ) O2 sensors won't operate until they get up to temp. And the only warmth that they have is the exhaust. So the closer they are the better.
Heated ( 3 wire or more) O2 sensors are not as sensitive to placement but will get up to temp faster the closer that they are to the engine.
Orientation matters.
When warming up the engine produces a tremendous amount of condensation and some of that collects on the O2 sensor.
If the sensor is oriented to allow for the collection of this condensate.That moisture stays inside the housing and increases warmup time. It also shortens the sensors lifespan dramatically.
Most sensors, with the exception of the later AFR sensors need a supply of clean air. They use that air as a comparison sample.
This sample is taken from a small filter on the side of the sensor housing or through the wiring harness sheath.
Clean, preferably cool air is required. Oil and coolant contamination is common and will cause all kinds of sensor reading flaws.
Exhaust leaks are clearly not allowed. Even a small crack or incomplete weld will make the sensor reading useless.
Heated sensors can be used anywhere in the system. With a couple of caveat's. They must be located before the Cat. if you have one. And while they could be mounted right on the tail pipe. They must be far enough up the pipe to avoid contamination of the sample from simple reversion. But closer to the engine is still best.
Lastly, the exhaust system needs to be grounded.
For one and three wire sensors in particular it's critical.
And also to reduce the electrical noise in the pipes for an AFR sensor as well.
You would think that this was a non issue but, rubber hangers, organic gaskets and a touch of rust can leave the entire exhaust system without grounding more often than not.

That's all I've got for now kids.
Fred

Pretty comprehensive.

Jim

If you have the option "to open your headers" how far should the sensor be away from the opening?