I have this /6 exhaust manifold with a big hole in the side, plugged with a nut. Never seen one like it before. It looks to be a factory machining operation.

I'm guessing it has to do with some kind of emissions setup that somebody didn't want and just plugged it?

What is it off of? I have never seen one like that. O2 sensor maybe?

I can't remember what it came off of; it was in my stash from years of going to the 'yards.

I can't find a Chrysler part # on it anywhere like all the others I've seen. It might be aftermarket.

I would guess it's a later manifold and the hole is for air injection (think car), the plug means that the donor didn't have air injection (think truck).

Pretty sure the /6 went away before O2 sensors.

A couple more pics. The machining on the outlet looks different from any other one of these I've seen. The mystery hole looks like it was machined at a factory - not some backyard hack job.

Ive had some 81-88 cop cars and they had what looked like o2 sensors on drivers side

Can you show a pic of the entire manifold?

Yup.

EGR port?

That looks like an A.I R. port. Air Injection Reactor. The "smog pump" forced fresh air into the exhaust stream to aid in the reduction of unburned gases in the exhaust stream. Many mid 70s and later 318 and 360 manifolds had this, certainly the slant six employed similar tactics.

Slants ran the air pipe into a port beside the rear exhaust port.

It's not for AIR. That is most likely in the exhaust port, same as a 318.

I started out thinking it was for O2 sensor as Slants had to have O2 sensors before going away, probably from 1980 or 1981. Emissions standards were too strict and required the use of 3-way catalysts which only work with an O2 sensor.

The threads are right for an O2 sensor, same as a spark plug. The factory plug says it was a factory hole, as does the boss on the manifold.

It could also be a source for exhaust gas for EGR.

Whichever it is, it would be a really handy manifold to have if one was considering using an O2 sensor either for carb tuning or to run a fuel injection system.

Probably about this time some old Chrysler mechanic will tell us what it really did.

R.

I have an '83 Parts Catalog - it shows two /6 exhaust manifolds

4100445 - w/N95 - emission controls testing & label (California emission controls)

4186239 - w/N93 - Canadian & Export emission package ,N98 - without Lean Burn (ESA - electronic spark advance)

I couldn't identify any wire harness/switch/sensor/air pump/EGR/O2 that clearly identified the difference

That would make sense since it came out of a California yard.

But, no Mopar casting number anywhere, but I did find what looks like "China" and probably a date of 12079.

So, I'm assuming an aftermarket piece for an early 80's California vehicle.

here's a NOS #4100445 N95 emission manifold that was on eBay advertised as '79-'82 - can almost make out the machined hole's location?

83 diplomat on rockauto is showing an o2 sensor for slant six. Im with the o2 crowd

From what I remember its for the 02 sensor. I remember working on an 87 Dodge van with the slant six in it. They had 02 sensors in the slants even whith a carburetor as they used feedback electric carbs and leanburn used electronic controlled carbs. Ron

I found this over on the Slantsix.org board:

"We will review the different exhaust manifolds available for the SL6 and discuss manifold preparation / installation
All SL6 exhaust manifolds are basically the same and will interchange with all SL6 engines 1960-86. There were some minor changes made to the exhaust manifolds over the years which added more reinforcement ribs and changed the choke stove pocket design. The first SL6 exhaust manifolds had no external ribbing and as a result, these crack and break easily. From these first manifold castings, this long cast iron exhaust manifold would prove to be a challenge to keep in one piece, as a result, the engineers added reinforcement ribs in an attempt to prevent cracking. Two external ribs were added in 63 to stiffen the body of the manifold. 1970 saw another bottom rib and ribs running up each runner "leg" added, along with a revised (round) heat riser valve counterweight. By 1980 a thick section was added to the heat riser area's rear wall and this "boss" was drilled and tapped for an O2 sensor."