O2 Sensor / Exhaust Balance Pipe

[Lance]

A few queries for you knowledgeable chaps out there.
I note that, usually, in the GT40 exhaust systems I’ve seen the O2 sensor is connected into one branch of the exhaust, which means it’s reading only half of the motor. My thought is that it would be best for it to be reading all cylinders. There may be little difference, but what is the accepted practice on this? I’m looking at building a plate into the system to achieve this (as per the attached sketch). The internal gallery in the plate would also act as a balance pipe. Balance pipes are also supposed to help quieten and improve (?) the exhaust note. Has anyone used a balance pipe on their GT40 exhaust? Are they worth the effort? The trouble with my proposal is that the ‘balance pipe’ won’t be the ‘recommended’ 75% of the cross sectional area of the pipes it’s joining. Does anyone know how crucial this is?
I’d be interested to hear whether it’s all considered to be worth the effort. Thanks for any help.

 

[Bob Putnam]

I would be afraid of two things:

1. Not enough flow between the banks if you are using the "normal" 180 degree layout.
2. A block like that is going to slow the sensor's rise to working temperature (in conjunction with the low cross-flow).

I think you're better off to use a single sensor directly in one of the banks flow. Better response to what are very time-sensitive inputs. There's probably not going to be much variation between banks anyway, unless there is a mechanical problem. Then, your "averaged" signal is still going to be bogus, so you've gained nothing.

 

[Randy V]

Yep - Not enough flow... I don't even think it would work properly with a heated wideband.

Now if you were to come up with an "X" pipe and place the sensor in the centre of the union, you'd have something that should work pretty darned well I would think...

 

[Seymour Snerd]

...I note that, usually, in the GT40 exhaust systems I’ve seen the O2 sensor is connected into one branch of the exhaust, which means it’s reading only half of the motor. My thought is that it would be best for it to be reading all cylinders. There may be little difference, but what is the accepted practice on this?

Assuming we're talking about wideband sensors, it seems to me you could get the same effect using two mechanically separate sensors and electrically averaging their outputs.

 

[Julian]

Lance, I think you're sort of missing the point of balance pipes here. A crossover GT40 type of exhaust header arrangement negates the need for a balance pipe. The balance pipe is included in normal separate V8 headers to try and even out the exhaust pulses, whereas a crossover header system has already achieved this.

Regarding O2 sensors...it don't really matter unless you are super concerned with emissions. Not unusual for early unleaded cars to have an 02 sensor in just one bank (V6 VN Commodore as an example). Depends what the 02 sensor is being used for I guess. Wide band tuning aid, narrow band closed loop control of ecu, wide band closed loop ecu control (assuming your ecu can do this)...

 

[Randy V]

Lance, I think you're sort of missing the point of balance pipes here. A crossover GT40 type of exhaust header arrangement negates the need for a balance pipe. The balance pipe is included in normal separate V8 headers to try and even out the exhaust pulses, whereas a crossover header system has already achieved this.

The first production implementation of the Balance Pipe that I'm aware of was in the early 60's by Ford Motor Company. The implementation was not to change the performance but sound. The V8 engine will only fire one cylinder at a time. The pulse from each cylinder firing would be shared between 2 mufflers (which could be smaller in size, easier to fit/package within the chassis and produce less heat in the area of the muffler.
The side benefit was increased performance via the reduction in overall back-pressure.

The cross-over exhaust system of the GT40 does not share/split the pulses between both mufflers. Each pulse sees it's own muffler.

Regarding O2 sensors...it don't really matter unless you are super concerned with emissions. Not unusual for early unleaded cars to have an 02 sensor in just one bank (V6 VN Commodore as an example). Depends what the 02 sensor is being used for I guess. Wide band tuning aid, narrow band closed loop control of ecu, wide band closed loop ecu control (assuming your ecu can do this)...

Not so sure here... Many closed loop systems rely on accurate feedback from the o2 sensors to keep things close to stoich not just from an emissions perspective. Your example from the V6 Commodore is one that I've not seen before.. Quite interesting really...

 

[Jack Houpe]

Lance based on the fact that all your injectors are equal just having one O2 sensor should be just fine. If you feel you have a cylinder imbalance then I would prefer to use exhaust temp as a method of correct air fuel ratio. If it feeds a closed loop system you will have to make sure that your headers don't leak as the slightest air in the system will cause the computer to oscillate lean rich, lean rich. I prefer not to use closes loop.

 

[Lance]

OK, then.

Sampling all the cylinders not required. Check.
Plate mounted O2 sensor not a satisfactory format and no room for X pipe or similar. Check.
Limited, if any, side benefits of a balance pipe to be had anyway, in this configuration. Check.

Assuming monitoring all cylinders WAS an advantage, I was mainly hoping for a few ‘free’ dB noise reduction from the balance pipe. I note that my 850 Norton (one pipe per cylinder, so no phasing of exhaust pulses required) had a balance pipe, supposedly for improved power and noise reduction reasons. Anyway, this is obviously not on, so a single sensor on one side of the exhaust it is, then.

Thanks for the input, chaps. That’s saved me a bit of messing around for no gain.

Cheers,

Lance.

 

[Karen Brady]

I think it really depends on you but i think having to oxygen sensor is better than one because the goal of the sensor is to help the engine run as efficiently as possible and also to produce as few emissions as possible.

So what is the purpose of having it sold to us with only one oxygen sensor? But i think your a bit right if your thinking green then that is good. But i guess you will only add that if your really have lots of cash but i will just go with only one o2 sensor!