O2 sensor position/placement

[laserbeamasaur]

Hello errbody,

I'm rebuilding the engine in my 85 4runner and I'm at the point where I'm thinking about headers.

I noticed that a lot of different headers have significantly different O2 sensor placements. Does this matter at all?

Just an example of this:

OBX has the O2 right before the cat
Product Name - OBX Racing Sports

Hedman has it on a single exaust tube
Hedman 39498 Hedman Hedders Elite Headers

Thanks

 

[WarDamnEagle]

I think it's better after all the exhaust tubes have come back together, ie after the header. Otherwise you're only measuring the O2 content of one cyclinder. Of course theoretically that should suffice but if I had the choice I would go downstream.

 

[pappy]

I think it's better after all the exhaust tubes have come back together, ie after the header. Otherwise you're only measuring the O2 content of one cyclinder. Of course theoretically that should suffice but if I had the choice I would go downstream.

EXACTLY!

I have an old Doug Thorley header on my 85 4Runner. The OX sensor was mounted on one tube. I had issues passing smog at idle. The theory was since only one cylinder was feeding the tube the sensor was going cold. After a lot of thought I had a muffler shop install a standard screw in sensor bung between the header and the cat. Because this was a long way down stream I installed a heated sensor. I have had no issues since.

Install the fitting in the collector tube on the header and you might get away without needing a heated sensor. I have seen unheated sensors quite a way downstream on other cars that seem to work. Maybe someday I'll unplug the heater wire on mine and see what happens.

 

[laserbeamasaur]

Okay, sweet. Thanks for the help.

I was planning on getting the OBX setup anyway. I'll just use the stock sensor and see if that works otherwise I guess I'll go with a heated one too. I'll let you know how it goes.

 

[WarDamnEagle]

Before you buy, have you looked at the LC Engineering stainless header? I'm pretty happy with mine.

 

[jynx]

Not to throw a wrench, but the stock manifold is about all you need for these motors unless yours is shot and a replacement is a no go. Read some info on 4x4wire several years ago posted buy what I would consider to be a 22RE guru that made a very compelling argument for a stock manifold, 2" to and thru cat and then 2.5" cat back.

Just some food for thought.

 

[KLF]

My first LC Engineering header had the O2 sensor on one of the collectors, right below the brake master cylinder. Occasionally I would get a Check Engine flash, but the code was never being stored in the ECU, so I just ignored it.

When that header rotted apart (after many many miles), I bought another one, ceramic coated this time. The one had the O2 sensor bung way down on the connector between the end of the header and the cat, they included a length of special wire and crimps to extend the wiring. Once that one was installed, no more MIL flashes.

 

[KLF]

Not to throw a wrench, but the stock manifold is about all you need for these motors unless yours is shot and a replacement is a no go. Read some info on 4x4wire several years ago posted buy what I would consider to be a 22RE guru that made a very compelling argument for a stock manifold, 2" to and thru cat and then 2.5" cat back.

I don't really care what some "guru" wrote, I can attest that when I installed my LC Engineering header, I could tell the difference. Maybe part of it was from the change in sound and the $350 lighter wallet, but the engine ran better.

 

[pappy]

Not to throw a wrench, but the stock manifold is about all you need for these motors unless yours is shot and a replacement is a no go. Read some info on 4x4wire several years ago posted buy what I would consider to be a 22RE guru that made a very compelling argument for a stock manifold, 2" to and thru cat and then 2.5" cat back.

Just some food for thought.

Strongly disagree. When I installed my DOA engine over a decade ago I used the stock manifolds. Later, I installed the Thorley header into the factory exhaust. There was a very significant difference and the header really brought that engine alive. I later installed the 2.25" exhaust behind it and noticed another significant difference.

Your source of information is very suspect. A 2.5" exhaust is way overkill for a small 22RE. I've even considered dropping my exhaust size down to 2" from the muffler to the tailpipe to try and improve the low end torque. Huge pipe works great when you are pushing lots of exhaust, like from a V8. You significantly impact scavenging, and hence low end torque, when there is turbulence in the pipe due to low velocity.

 

[snobdds]

Not to throw a wrench, but the stock manifold is about all you need for these motors unless yours is shot and a replacement is a no go. Read some info on 4x4wire several years ago posted buy what I would consider to be a 22RE guru that made a very compelling argument for a stock manifold, 2" to and thru cat and then 2.5" cat back.

Just some food for thought.

I remember hearing this too, so I had to search the interwebs to find out where I heard it. Turns out, Ted from engnbldr is the one who said this...

>>>*This is one I saw tested many times, even to a series of dyno tests on an older carbed 22R. The same results were seen on the EFI versions.

The factory manifold is excellent and holds the correct back pressure at the port exit to control crossflow at the valves. The stock exhaust pipe is a bit too small, a sacrifice the factory made for noise.

We found a 2" primary pipe size all the way to the muffler entrance, then 2 1/4" on exit all the way back is the best all around. Smaller restricts and some power/economy is lost. Larger frees her up a bit too much and tends to soften the lower end response. It's easy to do since a lot of mufflers are available this way right out of the box, directional flow gains are well known in the industry.

The small increase in pipe size at the muffler encourages directional flow since any restrictions or reversions in the pipe itself are always a detriment.

The drawback is the engine will make more sound, that depends of course on the muffler design, also.....*EB

4x4Wire's TrailTalk Forums: 2" or 1 3/4" exhaust on 84 22r carbed=

So who knows, I do trust Ted and his long knowledge on this topic. I have always stuck with the stock manifold and it has been good to me. I have always been told that a header only works if there is a free flowing intake and larger throttle body, and larger and higer spring rate valves.