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V8 - O2Bung in single tube vs collector

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I am running a Ford 427FE V8 with a Borla EightStack injector system(individual runner). My ECU is a Performance Electronics 8400. When I installed this system, I chose to put the O2 sensors, one each side, in the collector on the side pipe. About 25 inches from the exhaust valves and also about 30" from the end of the exhaust pipe. Haven't had issues with reversion but I know I am on thin ice. Because of the proximity of the collectors to the body and wishing to keep them out of view, it was very difficult to get them in.

I am working on a new build and a local highly respected tuner is touting the idea of just putting the O2 sensor in an individual tube rather than the collector. Since my system is capable of running in a timed/sync mode, I know it could be screwed up but as long as I was careful, is the averaging of lambda a dangerous or bad thing.

Curious what others may think. It sure would simplify the installation of the sensors. I'd still run one on each side - and could chose which pipes they would mount to so as to kind of balance the reading in the rpm cycle.

Thoughts or comments? Am I looking for issues?


Sounds like it is going to be a very cool build - not going into a replica Mk4 GT40 by any chance?

I think you already know the reason it is better to have it in the collector(s) - that way you will get the average for that bank of cylinders and be less likely to have the other cylinders out of tune. I mean if the one cylinder you chose happens to be a little richer, or leaner, than the average, by tuning to that the others will be further out - using the collector(s) doesn't mean they will all be 'right' but they may be expected to be closer.

However, as you 'should' have identical cylinders, with IR runners, if you have the same length exhausts as well, they should be very close to the same and so it 'should' work - if you were running a single plane plenum manifold air and fuel variations are common, so maybe not the best.

Oh, be careful with the filter choice, if used, as some of the individual mini filters that fit over the stacks can be VERY restrictive with some back to back testing showing around 20% power loss - that will badly screw up the ignition and fuelling, so if using them on the road and removing them for the track, you will need two maps.

If you're going to consider adding two bungs to the header primary pipes, adding bungs for all 8 would allow you to move the O2 sensors around and block off the 6 you're not using. I haven't seen as much per-cylinder lambda data as I'd like, but from what I recall the cylinders seemed to 'steal' air from each other... during one dyno pull the data from Cyl1 might be richer than Cyl2 at a certain RPM, then leaner at a different RPM, then richer again. In other words, the data from just one or two of the primary pipes might trick you into building odd shapes into a fuel map. Because of this, it might be nice to have at least one bung after the merge collector in order to avoid second-guessing yourself due to the new sensor location.

I'd personally be reluctant to use a single runner for tuning the entire bank of cylinders unless I already knew that the cylinder to cylinder balance was pretty much on point. I guess if it's from an aesthetics and packaging consideration then you need to decide where your want to focus your efforts and perhaps the accuracy of the tuning will take a back seat.

Thanks, guys - that kind of confirms what I was thinking but wanted to reach out to the experts. Now, I wish I could come up with an O2 sensor that was half the size of the current ones, and would work safely angled down.

Oh well, back to the drawing board.