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 Post subject: O2 sensor placement
PostPosted: November 27, 2022, 3:42 pm 
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Joined: August 28, 2010, 7:53 am
Posts: 343
I just built a custom header for my supercharged chevy 2.4 Ecotec. The header is a 4-2-1. Primaries are about 10" long.

Is it best to put the O2 sensor close to the head, but only working on one cylinder, or should I put it at the collector between 2 cylinders?

The final merge from 2-1 is pretty far from the engine, as the secondaries are quite long.

FWIW - I am running a custom wiring harness and reprogrammed ECU from CBM motorsports.


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 Post subject: Re: O2 sensor placement
PostPosted: November 27, 2022, 8:06 pm 
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Joined: July 17, 2008, 9:11 am
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Location: West Chicago,IL
I would put the sensor after the last merge. That way it is averaging all 4 cylinders. If you are using a heated O2 sensor it shouldn't make a difference where it is located. Even using a single wire, non-heated sensor it should still work.

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 Post subject: Re: O2 sensor placement
PostPosted: December 1, 2022, 7:07 pm 
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After the last collector and on the top half of the pipe.

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 Post subject: Re: O2 sensor placement
PostPosted: December 2, 2022, 7:34 am 
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Joined: August 28, 2010, 7:53 am
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Thanks Guys - I just ordered a weld in bung that it angled 45* for extra clearance, since there is only about 1-1/2" between the collector and the body

FYI Verocious Motorsports has them, as well as all the tubing etc I used for my exhaust. Very good products and service
The flex bellows they sell are made by vibrant which have pretty bad reviews online (FWIW)

I bought mine from GBE Mandrel in Oregon. These guys make their own - Products and service are A+++++


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 Post subject: Re: O2 sensor placement
PostPosted: December 2, 2022, 9:44 am 
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Joined: December 18, 2010, 3:29 pm
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So I had a very similar setup and got different advice and put it in a primary 18" from the head. I was told by AEM that the heated sensor would still run too cold at idle if it was more than 18" from the head on a non-catalyzed setup. Even though you only get one cylinder it's outweighed by the proper gas timing (has to line up with the delay you have in your engine control software) and temperature range.

On the last car I had it was in the collector (but closer) and both have worked similarly. I check plugs on this one to make sure the cylinders are basically balanced. Got a bit sticky because I had planned to weld it in the collector which was super accessible but then had to get creative with the welder since I didn't want to pull the whole thing off again.

Alex

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Last edited by ajmacdon on December 2, 2022, 4:50 pm, edited 1 time in total.

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 Post subject: Re: O2 sensor placement
PostPosted: December 2, 2022, 4:11 pm 
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Joined: April 23, 2019, 4:30 am
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I have never had to weld looking in a mirror, will put that one away in the memory banks as a get out of jail free card, beautiful work.


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 Post subject: Re: O2 sensor placement
PostPosted: December 2, 2022, 4:48 pm 
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Joined: December 18, 2010, 3:29 pm
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Kinetic Research wrote:
I have never had to weld looking in a mirror, will put that one away in the memory banks as a get out of jail free card, beautiful work.


90% of the time the weld ends up "reinforced" with plenty of tungsten but the welding gods were smiling that day :D

Alex


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 Post subject: Re: O2 sensor placement
PostPosted: December 2, 2022, 8:04 pm 
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Joined: August 28, 2010, 7:53 am
Posts: 343
Thanks Alex -

The collector for the 2 rear cylinders is about 14" from the head, which was my original Idea for the location.

Are you saying that the ECU has to be programmed differently if reading off of 1 or 2 cylinders, rather than all 4?

I attached a pic of the primaries coming off the head.

BTW, your build is really awesome!


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 Post subject: Re: O2 sensor placement
PostPosted: December 4, 2022, 2:56 pm 
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Joined: December 18, 2010, 3:29 pm
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Sean in CT wrote:
Thanks Alex -

The collector for the 2 rear cylinders is about 14" from the head, which was my original Idea for the location.

Are you saying that the ECU has to be programmed differently if reading off of 1 or 2 cylinders, rather than all 4?


No, I'm not talking about a calibration for the number of cylinders being measured, I mean that there's a calibration in most aftermarket ECU's for delay from combustion event to O2 sensor reading. It depends on how long it takes the gas to get from the chamber to the O2 sensor (and, I assume, the characteristics of the sensor itself?). In a factory system or a tuned factory controller I imagine you want it to be somewhat close to the factory distance. It's a tiny number, 200ms or something, but I worry that pushing the sensor 30+" from the head will probably come into play. I didn't want to have to worry about it which was part of my decision to keep it close.

In your case I personally would put it in/just after one of the first 4-2 collectors 14" from the head. You get info from 2cyl and you keep under the AEM recommended 18" number. I'm no expert, though, just sharing what I decided based on advice from one source!

Alex


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 Post subject: Re: O2 sensor placement
PostPosted: December 4, 2022, 8:08 pm 
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Joined: August 28, 2010, 7:53 am
Posts: 343
Good answer :D I welded in the collector for cyl 3/4 this am Thanks for clarifying


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