Oxygen sensor

[cudabob496]

I have a 3 inch X pipe dual exhaust.
Where should I place the O2 sensor?
Thanks

[BS CUDA]

I have a 3 inch X pipe dual exhaust.
Where should I place the O2 sensor?
Thanks

 If you check TTI's website they show the O2 in the header collector tube - I installed mine directly behind the header to exhaust flange as I didn't want to drill the ceramic coated headers. Works fantastic - Innovate wideband with Bosch sensor.

[Chryco Psycho]

I agree , just past the header into the X pipe will work great

[Strawdawg]

remembering that a very small leak between the head and the sensor will cause it to read lean-particularly at lower rpms

[cudabob496]

remembering that a very small leak between the head and the sensor will cause it to read lean-particularly at lower rpms

could you elaborate "leak between head and sensor will cause to read lean"
Want to make sure I don't have that problem.
leak where specifically?

[cudabob496]

dang, Summit just dropped the price on the AEM sensor to $154.
A summit guy said he had one and it worked great.
also, the clamp and bung that goes on the exhaust pipe is down to $34.

[cudabob496]

Just put the AEM A/F meter in. Seems to work great!

Cruised around a little, and meter was steady at about 10.5, so that means
my 84/84 jet size selection for primary and secondaries in my 850 Holley is too high. I'll drop
the primary first to 80 to see what happens!

[Strawdawg]

could you elaborate "leak between head and sensor will cause to read lean"
Want to make sure I don't have that problem.
leak where specifically?

What I said...any leak between the engine and the O2 sensor will cause the sensor to read incorrectly as  the air/fuel mix will be contaminated by outside air instead of solely being what came out of the combustion chamber

[cudabob496]

What I said...any leak between the engine and the O2 sensor will cause the sensor to read incorrectly as  the air/fuel mix will be contaminated by outside air instead of solely being what came out of the combustion chamber

The Sensor line is pressurized to 50 psi to check for leaks, prior to being sold.
Are you saying the line is leaking, and the reading is inaccurate?
At this point, the sensor is saying my carb is jetted too rich.

[Strawdawg]

I am not saying anything about your system because I am not looking at your system.  I was trying to alert you to problems that arise if there is a leak in the exhaust before the sensor

What I have tried to say twice above is that any leak in the exhaust system between the exhaust port and the sensor location will allow external air to enter the exhaust flow and make the the A/F's displayed leaner that what they actually are.  Also, if the sensor is located too close to the exhaust outlet, then the displayed A/F's will also be too lean.

Various manufacturers quote different distances but it is not uncommon to see a suggestion of ten times the exhaust diameter to be the minimum distance for the sensor's location from the exhaust outlet.  This minimizes the risk of the readings being affected by the surrounding atmosphere.

In both cases, the problem is most significant at lower rpm...say below 3000 rpm

[cudabob496]

I am not saying anything about your system because I am not looking at your system.  I was trying to alert you to problems that arise if there is a leak in the exhaust before the sensor

What I have tried to say twice above is that any leak in the exhaust system between the exhaust port and the sensor location will allow external air to enter the exhaust flow and make the the A/F's displayed leaner that what they actually are.  Also, if the sensor is located too close to the exhaust outlet, then the displayed A/F's will also be too lean.

Various manufacturers quote different distances but it is not uncommon to see a suggestion of ten times the exhaust diameter to be the minimum distance for the sensor's location from the exhaust outlet.  This minimizes the risk of the readings being affected by the surrounding atmosphere.

In both cases, the problem is most significant at lower rpm...say below 3000 rpm

OK, well, thanks for the heads up. The exhaust system seems to be tight right now, with the header bolts secure and the exhaust pipes bolted tightly to the
header collector. Also, if there was a leak in the exhaust system, I would suspect the exhaust, due to positive exhaust pressure, would leak out, rather than air leaking in.  But, exhaust systems can also have a scavenging effect.  Also, my A/F meter is reading 10.5, not the ideal 14.7. If there was air in-leakage, the meter would be reading well above 14.7, most likely, showing an abnormally high Air to Fuel ratio.

[nqkjw]

I was told to put a bung in 12" to 16" past the X in my system.

[brads70]

I have mine in the top of the header collector. As per Autometers instructions.

[cudabob496]

Ya, I'm about 1 ft past the header collector, just before the X pipe. Important consideration
is the sensor getting too hot, per AEM instructions. Just drilled a hole (well ground out/filed a hole), and clamped
on the bung. Has a high temp gasket to prevent leakage around sensor. Once I warmed up, when cruising, the reading
was very stable, at 10.5. Just changed jets to 80/84, from 84/84. Will report how A/F ratio changed. Engine has great power,
so I thought my 84/84 was fine, but, not according to the meter!

[Strawdawg]

OK, well, thanks for the heads up. The exhaust system seems to be tight right now, with the header bolts secure and the exhaust pipes bolted tightly to the
header collector. Also, if there was a leak in the exhaust system, I would suspect the exhaust, due to positive exhaust pressure, would leak out, rather than air leaking in.  But, exhaust systems can also have a scavenging effect.  Also, my A/F meter is reading 10.5, not the ideal 14.7. If there was air in-leakage, the meter would be reading well above 14.7, most likely, showing an abnormally high Air to Fuel ratio.

We are dealing with a gas and not a liquid and we are dealing with exhaust pulses, not a constant supply.  Therefore, outside air is easily pulled into the system and often screws up tuning of a closed loop f.i. system as the actual a/f  in the combustion chamber ends up on the rich side because the tuner was fooled by the leaner than reality a/f's being displayed.  We are dealing with an open loop system so we make the car richer than it should be instead of the car's computer doing it. As I stated above, this problem is worse at lower rpm because the exhaust pulses are not emulating a steady stream with more constant pressure.

But never mind, it does not matter whether you understand how it works.  As long as you don't have exhaust leaks before the sensor and the sensor is not close to the end of the outlet, all is good. 

I will mention, however, that on a carbureted car that 14.7-1, which is the stochiometric ratio, is usually too lean due to poor atomization of the fuel into the air stream and that somewhere around 13.0 to 14.1-1 usually provides a much more stable idle (the bigger the cam, the richer the required idle a/f) whereas about 14.2 is usually pretty close at cruise.

On a sequential port injection set up, 14.7 is the stochiometric ratio for the most complete, cleanest burn, but many of us have found that something higher than 15 may give the best gas mileage.  Carbs simply do not mix the fuel and air as well and end up needing richer numbers

I guess it is obvious that all the numbers above apply to idle or cruise and not wide open throttle which will be closer to 12-1 depending on what makes the most power without detonation