locating an O2 sensor in a side pipe

[bobcowan]

Originally Posted by eschaider

One of the fixes for the problem is to take the flange on the headers (between the engine and side pipes) and move the flange back an inch. After you have moved the flange back make a stainless square block that will fit between the headers and the side pipes. Mill out the center of the block leaving a large square opening. Weld an O2 sensor bung in a horizontal position.

Assemble the headers and side pipes with the stainless block and gaskets between them. Tighten everything up, screw in your sensor of choice and go for it! Your sensorial be where the calibration engineers wanted it, in terms of distance from the exhaust port so warm up and signal delay will be "normal" in calibration engineer terms.

Ed

I can't imagine this would be good for header performance. I'm guessing that you'd loose all or most of your pulse vacuum.

Originally Posted by eschaider

Most of the sensor manufacturers will caution us about sensor placement that allows moisture to collect in the sensor. They will encourage either a 3 o'clock or 9 o'clock sensor positioning. A 2 o'clock or a 10 o'clock sensor positioning will also work but a 4 o'clock or 8 o'clock sensor positioning is not recommended because of the potential to collect water.
Ed

I have read this before. I think I've even said this before. And it makes logical and engineering sense. The sensor pictured above has been there more than 6K miles. No codes, so I'm guessing they're working OK.

My FFR had the sensors in the same place for about 12 years without any problems.

I suspect it's not as big of an issue as we think it is.

The advantage to placing the sensor in the collector is that it samples four tubes/cylinders. Yes, it's kind of a long way from the chamber. But the computer can easily compensate for that and give a good accurate signal.

[olddog]

Originally Posted by bobcowan

I have read this before. I think I've even said this before. And it makes logical and engineering sense. The sensor pictured above has been there more than 6K miles. No codes, so I'm guessing they're working OK.

My FFR had the sensors in the same place for about 12 years without any problems.

I suspect it's not as big of an issue as we think it is.

It's not a big deal in a Cobra that is almost never driven in the rain and even less likely to sit outside overnight in the winter. Try it in a daily driver when you can watch water spewing out of the exhaust pipes and you will get a different result.

Originally Posted by bobcowan

The advantage to placing the sensor in the collector is that it samples four tubes/cylinders. Yes, it's kind of a long way from the chamber. But the computer can easily compensate for that and give a good accurate signal.

If you have a good intake and header design, all four cylinders will be the same. If this were not the case the leanest cylinder would get toasted. So the one pipe verses four pipes, although not ideal, is not nearly as big of a deal as too great of a distance. Exactly how far is too far, depends on what criteria you are using.

Let me talk process control in general. The computer can only control the process it is connected to. You cannot make it respond any faster than the process is designed. When tuning a PI control loop the gains can be calculated by: proportional gain Pg = Pk / (Tc * To) where Pk is the process gain (ratio of measurement change / output change); Tc is the time constant, and To is the dead time (time it takes the measurement to see an output bump). The absolute worst thing you can design into any process is a long dead time. With a one minute dead time the control variable is changing for a minute, but the computer cannot see it and react to it until that minute is up. As the controller makes the correction to come back to set point, there is the same dead time issue causing overshoot. This forces you to use a smaller gain to keep the loop from going into an ever increasing osculation that spirals out of control. Thus you have massively increased the response time of the control loop.

Now EFI does not use traditional P or PI or PID controllers, but the concept still applies. EFI control is brilliantly different, and it responds better in some ways. It rapidly makes ballpark corrections and very slowly dials in to spot on. It also handles an extremely noisy measurement from the O2 sensor.

[eschaider]

Originally Posted by bobcowan

I can't imagine this would be good for header performance. I'm guessing that you'd loose all or most of your pulse vacuum.

Bob,

The arrival of the negative pressure wave at the exhaust port, what you identify as pulse vacuum, will still occur, it's timing will just be too early to provide any improved midrange scavenging. The early arrival is exclusively due to the short length of the header pipe and the reduced time to travel the distance between the valve and the newly created O2 sensor chamber between the header and the side pipe. While that sounds bad, and in fairness it is not good, the length of our side pipes tunes that pulse to a very low rpm because of their extraordinary primary length.

That low rpm tuning will enhance low speed engine torque at the expense of mid range and higher rpm torque. That said, it is possible our side pipes may produce no more power than a good low restriction under car exhaust. The reason that they may not, primary length not withstanding, is that the original side pipe mufflers that came with our cars tend to be fairly restrictive.

There are several aftermarket side pipe alternatives that look less restrictive than most original mufflers. As good as our side pipes look, a good, large diameter undercar exhaust with more traditional muffler geometry may produce a net power increase.

Bottom line I suspect, but don't have data to support the suspicion, that the chamber for the O2 sensor (between the header and the side pipe) will not materially, effect engine power enough that the driver can feel it.

Originally Posted by bobcowan

I have read this before. I think I've even said this before. And it makes logical and engineering sense. The sensor pictured above has been there more than 6K miles. No codes, so I'm guessing they're working OK.

My FFR had the sensors in the same place for about 12 years without any problems.

I suspect it's not as big of an issue as we think it is.

It is in all likeliness because of what Rick (olddog) was suggesting about usage frequency. The more frequently we operate the car the more frequently the sensor gets exposed to water condensation from a cold engine start.

At first glance, this does not seem to be a big deal however most O2 sensors do not just fail they tend to fade or drift with age getting increasingly less accurate until they finally give up the ghost and we need to replace them.

Along the way to giving up the ghost the AFR or lambda reading they communicate to the ECU results in a progressively incorrect AFR/lambda performance compared to the commanded target in the tune. On a high horsepower engine this mis-communication can bring on incipient detonation which the driver cannot hear but the pistons can feel.

The pic below is of a piston from an engine with 30K+ miles on it's tune that did not smoke but had become lazy. I am not trying to be cute, the engine still made significant power but it was becoming tless responsive to small changes in throttle position — it wasn't as much fun to drive.



When it was torn down all eight pistons looked the same. All pistons had all three rings still in place although the top rings were pretty beat up. The top has been removed in the photo above. Notice how nice the skirt still looks, not withstanding the damages to the ring lands.

Although they are bit pricier, the NGK sensors have an interesting attribute that depending on your perspective is either good or bad. That attribute is that the NGK sensor will not drift. There is more to this story than what it appears to be. As the NGK sensor begins to deteriorate instead of drifting it totally fails sending you a clear signal it is time for replacement.

One of the nice attributes of the 14 Point 7 wide band sensors, other than their stunning speed, is that they continually compensate for the sensor drift attributable to age, water, over heating etc. Eventually they will also need replacement but your AFR/lambda readings will be accurate all the way to the end of the line — sort of a poor man's NGK.

Originally Posted by bobcowan

The advantage to placing the sensor in the collector is that it samples four tubes/cylinders. Yes, it's kind of a long way from the chamber. But the computer can easily compensate for that and give a good accurate signal.

You're right about the newer ECU's being able to offer some drift compensation, Bob. However, as Rick has already pointed out this delayed reporting of the presence of oxygen in the exhaust (associated with a sensor that is far from the exhaust port) will produce a less desirable driving experience because the engine is not being properly fueled in real time.

Virtually all EFI systems today use some variation of fuel trim tables that over time essentially "learn" what the engine wants for fueling and eventually produce a pretty good driving experience. This is true until something like the O2 sensor begins to drift and the fuel trim tables are off because the O2 sensor is mis-reporting the actual oxygen content in the exhaust. This is further aggravated by a tardy sensor that is late in reporting how rich or lean the exhaust is. Both whoopses affect proper injector pulse width calculations and the ECU's ability to properly fuel the engine becomes progressively worse.

One of the really nice attributes of the 14 Point 7 sensors is their stunning speed. Properly placed in the exhaust system they produce the best real time reporting of oxygen in the exhaust allowing the EFI system to track the commanded AFR / lambda the tuner has programmed into the EFI system at the highest fidelity level the EFI system is capable of.

In general EFI does some pretty amazing things operationally, compared to carbs and distributors — even when we hobble it by not optimizing the installation. When we do optimize the installation the engine performance is for all intents and purposes, untouchable.


Ed

[MKS427]

One option, I have not seen mentioned, is a double collector at the side pipe flange. This does require new headers, but you are sampling 4 cylinders within 18" of the heads.
Mine came from GP Headers. The sensor is positioned a 6 o'clock, but it is on a downhill run. I believe FFR Coyote headers have the double collector.

[Gaz64]

Originally Posted by eschaider

Bob,

The arrival of the negative pressure wave at the exhaust port, what you identify as pulse vacuum, will still occur, it's timing will just be too early to provide any improved midrange scavenging. The early arrival is exclusively due to the short length of the header pipe and the reduced time to travel the distance between the valve and the newly created O2 sensor chamber between the header and the side pipe. While that sounds bad, and in fairness it is not good, the length of our side pipes tunes that pulse to a very low rpm because of their extraordinary primary length.

That low rpm tuning will enhance low speed engine torque at the expense of mid range and higher rpm torque. That said, it is possible our side pipes may produce no more power than a good low restriction under car exhaust. The reason that they may not, primary length not withstanding, is that the original side pipe mufflers that came with our cars tend to be fairly restrictive.

There are several aftermarket side pipe alternatives that look less restrictive than most original mufflers. As good as our side pipes look, a good, large diameter undercar exhaust with more traditional muffler geometry may produce a net power increase.

Bottom line I suspect, but don't have data to support the suspicion, that the chamber for the O2 sensor (between the header and the side pipe) will not materially, effect engine power enough that the driver can feel it.




It is in all likeliness because of what Rick (olddog) was suggesting about usage frequency. The more frequently we operate the car the more frequently the sensor gets exposed to water condensation from a cold engine start.

At first glance, this does not seem to be a big deal however most O2 sensors do not just fail they tend to fade or drift with age getting increasingly less accurate until they finally give up the ghost and we need to replace them.

Along the way to giving up the ghost the AFR or lambda reading they communicate to the ECU results in a progressively incorrect AFR/lambda performance compared to the commanded target in the tune. On a high horsepower engine this mis-communication can bring on incipient detonation which the driver cannot hear but the pistons can feel.

The pic below is of a piston from an engine with 30K+ miles on it's tune that did not smoke but had become lazy. I am not trying to be cute, the engine still made significant power but it was becoming tless responsive to small changes in throttle position — it wasn't as much fun to drive.



When it was torn down all eight pistons looked the same. All pistons had all three rings still in place although the top rings were pretty beat up. The top ring looks like it is missing in the photo above. It is not, it is actually still there! Notice how nice the skirt still looks, not withstanding the damages to the ring lands.

Although they are bit pricier, the NGK sensors have an interesting attribute that depending on your perspective is either good or bad. That attribute is that the NGK sensor will not drift. There is more to this story than what it appears to be. As the NGK sensor begins to deteriorate instead of drifting it totally fails sending you a clear signal it is time for replacement.

One of the nice attributes of the 14 Point 7 wide band sensors, other than their stunning speed, is that they continually compensate for the sensor drift attributable to age, water, over heating etc. Eventually they will also need replacement but your AFR/lambda readings will be accurate all the way to the end of the line — sort of a poor man's NGK.



You're right about the newer ECU's being able to offer some drift compensation, Bob. However, as Rick has already pointed out this delayed reporting of the presence of oxygen in the exhaust (associated with a sensor that is far from the exhaust port) will produce a less desirable driving experience because the engine is not being properly fueled in real time.

Virtually all EFI systems today use some variation of fuel trim tables that over time essentially "learn" what the engine wants for fueling and eventually produce a pretty good driving experience. This is true until something like the O2 sensor begins to drift and the fuel trim tables are off because the O2 sensor is mis-reporting the actual oxygen content in the exhaust. This is further aggravated by a tardy sensor that is late in reporting how rich or lean the exhaust is. Both whoopses affect proper injector pulse width calculations and the ECU's ability to properly fuel the engine becomes progressively worse.

One of the really nice attributes of the 14 Point 7 sensors is their stunning speed. Properly placed in the exhaust system they produce the best real time reporting of oxygen in the exhaust allowing the EFI system to track the commanded AFR / lambda the tuner has programmed into the EFI system at the highest fidelity level the EFI system is capable of.

In general EFI does some pretty amazing things operationally, compared to carbs and distributors — even when we hobble it by not optimizing the installation. When we do optimize the installation the engine performance is for all intents and purposes, untouchable.


Ed

Any more pics of those pistons Ed?
I find it hard to believe the top ring is fitted to that piston, I can't see it.
The engine must have pinging a lot, intermittently.

[eschaider]

Originally Posted by Gaz64

Any more pics of those pistons Ed?
I find it hard to believe the top ring is fitted to that piston, I can't see it.
The engine must have pinging a lot, intermittently.

That was the only one I kept, Gary. They all looked about the same. The top ring is no longer in the land in that pic. I know, the visual is stunning. Amazingly this engine did not smoke and still had significant power. The second ring was apparently doing the majority of the heavy lifting — not something it was designed for.

Unbelievably the detonation was undetectable to the ear while driving the car, windows up or windows down. It was however, just enough to overheat the crown and top land but not enough to push out a chunk of piston or burn through a ring. The other thing worthy of noting was the engine literally ran 30K+ miles with this condition after being tuned by a big name shop.

The tune was reportedly done for max power. The engine did not have any knock detection or correction protections / capabilities because it was an OEM ECU. The car was a supercharged 03 Cobra which made the engine more detonation prone. I believe it would be difficult but not impossible to do the same thing with an n/a engine — but who wants to test those sorts of waters.

The old lean is mean quip sounds good but does not play well in the real world. I always like to shoot for a whisker on the fat side just for good measure. That does not produce any meaningful decrease in power but it does produce a significant improvement in engine service life.


Ed

p.s. Almost forgot to mention, the second and oil lands were both tightened up a bit . The second ring was quite tight essentially keeping it from freely rotating on the piston. The oil land was also slightly pinched but not enough to limit ring rotation or compromise oil control yet.