O2 sensor location with Holley Sniper ll

[Sixflyer]

Getting ready for first engine start soon and I’m trying to decide where to install the o2 sensor. Using a 4.6 32 valve with Sniper ll on a Sullivan manifold with tube headers. Holley wants the sensor past the collector but it’s impracticable with the required mounting angle. I’m considering mounting just before the coupling in number three cylinder exhaust pipe. Do you think using that one cylinders mixture would be sufficient, not looking to track it, just cruising.

[burchfieldb]

Getting ready for first engine start soon and I’m trying to decide where to install the o2 sensor. Using a 4.6 32 valve with Sniper ll on a Sullivan manifold with tube headers. Holley wants the sensor past the collector but it’s impracticable with the required mounting angle. I’m considering mounting just before the coupling in number three cylinder exhaust pipe. Do you think using that one cylinders mixture would be sufficient, not looking to track it, just cruising.

You could call Holley and ask them, they have been super helpful for me, but not likley a good idea. Since you would only be reading one cylinder and could cause the others to run lean or rich.

[CraigS]

I think it can work fine but I would do some research first. Depending on intake manifold design (dual plane, single plane,etc) and carb type there has been some fairly standardized info on which cylinders are likely to run a little lean. So it would be good to choose one of those for your sensor. By carb type I mean do all 4 barrels in the Sniper open at the same time or are they progressive like most 4bl carbs where you are running on just 2 most of the time?

[Norm B]

I called Holley on this and they were pretty adamant that the O2 sensor went after the collector. The angle was less important to them. I put mine in the passenger side pipe just after the collector at a slight upwards angle. Chose the passenger pipe because it moves down under hard acceleration and thus the O2 sensor can be much closer to the body rocker panel area than it could on the driver side. Lots of heat there after shutdown so, very little chance of moisture issues which is the primary concern with the sensor angle.

[John Ibele]

I might be missing something, but if you have 4 into 4 headers and your collector is in the side pipe, I don't know why you wouldn't do what has been done many times successfully with this setup: mount the bung for the sensor in the side pipe just past the collector, with the sensor pointing slight up to avoid the body. This is counter to Holley instructions but has been done many times with roadster builds, as one of those compromises required to fit the roadster body. I had my bung welded as described in GasN pipes and have had no issues.

Here's the best photo I could find showing location from my build photos, looking forward on DS side.

Edit: Norm beat me to it while I was writing my post. To his point, I think the cable was plenty long to go to the PS side if desired. The compromise (if it even is one) is worth it in order to get information on 1/2 your cylinders vs. 1/8th.

https://live.staticflickr.com/65535/53097387447_5b1038d1d6_b.jpg (https://flic.kr/p/2oU2Zpn)
Untitled (https://flic.kr/p/2oU2Zpn) by John Ibele (https://www.flickr.com/photos/familycobra/), on Flickr

[phileas_fogg]

I mounted my O2 sensor in the collector at a slightly upward angle, same as Norm and John but on the driver side. No issues in 6 years.

Anecdotally, I haven't read about very many O2 sensor failures. My sense is that they are more robust than we think.


John

[MPTech]

Don't the new headers have a collector before the side-pipes? I thought this was the reason for this design.

[John Ibele]

Don't the new headers have a collector before the side-pipes? I thought this was the reason for this design.

They do. But I believe they are made to fit the Coyote engine, not the modular 4.6. So I’m expecting the OPs collector is in the side pipe.

[john42]

Don't the new headers have a collector before the side-pipes? I thought this was the reason for this design.

That's exactly where I put my O2 sensor for my Sniper2. Works perfectly fine.