O2 sensor in side pipe headers' collector
Thread Starter
Drifting
Joined: Apr 2001
Posts: 1,919
Likes: 272
From: Portugal
O2 sensor in side pipe headers' collector
I am planning to swap out my dual quads for a good EFI setup. One of the issues is the O2 sensor. I have side pipes. I plan to put it in the passenger side collector, and use a heated O2 sensor because it's so far from the engine there. I know I need to try to get it at a 10 o'clock position on the collector to minimize condensation in it inside the collector.
My question: How important is the header-to-side pipe flange? They are notoriously difficult to get fully sealed. Do you think oxygen from there will get "sucked back" forward the ~6" from that flange to where the O2 sensor will be located in the collector?
If yes, I am considering basically soldering that flange and planning to destroy the header/sidepipe if/when I need to remove it. I don't like that idea...
My question: How important is the header-to-side pipe flange? They are notoriously difficult to get fully sealed. Do you think oxygen from there will get "sucked back" forward the ~6" from that flange to where the O2 sensor will be located in the collector?
If yes, I am considering basically soldering that flange and planning to destroy the header/sidepipe if/when I need to remove it. I don't like that idea...
Race Director
Joined: Apr 2007
Posts: 11,150
Likes: 890
From: South Western Ontario
You can cut the bung on an angle and put the O2 sensor horizontally just below the frame. It'll be sticking out the side of the collector towards the bottom, but it'll be fine as long as the sensor is at least level.
You could use a little high temperature RTV on the joint to help with leaks.
You could use a little high temperature RTV on the joint to help with leaks.
Last edited by lionelhutz; Jan 11, 2017 at 12:36 PM.
Thread Starter
Drifting
Joined: Apr 2001
Posts: 1,919
Likes: 272
From: Portugal
You say you have not had any issues with apparent bad readings. Do you think your header-sidepipe flange does / does not have a leak?
Thread Starter
Drifting
Joined: Apr 2001
Posts: 1,919
Likes: 272
From: Portugal
Just to be clear, I know an exhaust leak in general will let oxygen into the exhaust flow. I am specifically asking if folks have experienced that oxygen flowing "upstream" (between pulses) from a leak "downstream" of the O2 sensor.
Are you saying you know that it will?
Thanks,
DD
Thread Starter
Drifting
Joined: Apr 2001
Posts: 1,919
Likes: 272
From: Portugal
You can cut the bung on an angle and put the O2 sensor horizontally just below the frame. It'll be sticking out the side of the collector towards the bottom, but it'll be fine as long as the sensor is at least level.
You could use a little high temperature RTV on the joint to help with leaks.
You could use a little high temperature RTV on the joint to help with leaks.
I did put high temp RTV on the joint when I first installed the sidepipes. I think they leaked from day one anyhow. That's why I'm saying I might solder the joint to ensure no leak (if I believe the oxygen will flow upstream). Do you have any other special techniques or practices you have used that work to get the sidepipe-header joint sealed completely reliably?
Instructor
Joined: Sep 2015
Posts: 249
Likes: 32
From: Cypress TX
Yes. it only takes the tinyest little bit of air to seriously skew the O2 measure, and if you're within 4x diameter, and anywhere near the collector it can swirl upstream.
One patch if only for tuning and not trying to long term run closed loop is wrap a wet rag around tip to keep a little back pressure and make the leak one way.
One patch if only for tuning and not trying to long term run closed loop is wrap a wet rag around tip to keep a little back pressure and make the leak one way.
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Melting Slicks
Joined: Feb 2001
Posts: 3,330
Likes: 13
From: Europe , Luxembourg
Hi
So why measuring in the collector bit and not further up the engine in a single pipe ?
Ok, this will read only 1 cylinder, but on a sound engine, that should be similar to the others ( except very outbd may be )
Rgds Günther
So why measuring in the collector bit and not further up the engine in a single pipe ?
Ok, this will read only 1 cylinder, but on a sound engine, that should be similar to the others ( except very outbd may be )
Rgds Günther
Thread Starter
Drifting
Joined: Apr 2001
Posts: 1,919
Likes: 272
From: Portugal
I think you answered your own question. The O2 sensor is there to detect "problems" along with optimizing the fuel mixture. So, as you say, if there is a problem and you're only measuring the one cylinder, then you won't know. You don't want the sensor to be in a location where it only monitors one cylinder. Ideally, (some new cars) have an O2 sensor for both banks of cylinders.
Racer
Joined: Nov 2010
Posts: 331
Likes: 108
I have not observed any unusual A/F readings. I think there is probably some positive backpressure in the system so leaks would be from inside out. The soot pattern at the joint in my old Hooker system seems to show that direction. I don't know if there is a net negative pressure at the joint between pulses but the pulse reflection should be from the step area change entering the collector and the O2 sensor is down steam 6-8 inches from the merge. If you're not sure there are some exhaust seal pastes on the market.
Grampy
Grampy