I didn’t get to work yesterday and the room with my computer in it, at home, is way too cold to spend much time in – so I didn’t get back to you.
They make an official exhaust manifold plug (V-8’s) or cylinder head plug (/6), but basically all three engine types (/6, small block and big block) use the same two designs.
To recap, the Aspirator and/or A.I.R. pump allows fresh air to reach a point not far behind the exhaust valve. The reason is: you have the heat and what little unburnt fuel – but lacking oxygen to complete combustion of the (what little) unburnt fuel is remaining.
Some people say this system reduces engine power because it pulls fuel from combustion chamber.
I don't quite see it that way, but will say the power output of engines with Aspirator/A.I.R. system typically is a little less than engines without same systems. People still debate this and have been for 40-50 years now.
My opinion is if system works, keep using it. If not working, then look at the options.
The /6 head was redesigned to allow for this system. A hole (a little less than 1” wide) is drilled almost length wise in the head. Then small holes are drilled into each exhaust port (about ¼“, each). The Aspirator (or A.I.R.) pipe bolts to rear of cylinder head. The same cylinder head was used for all /6 engines made, even for export (ie: with or without Aspirator or A.I.R. pump).
On the cases without, the OEM plate/plug bolted to that port - looks like this:
/6 is at rear of head at same level as manifolds (if equipped).
There is an alternatives one can use – which I’ll get to later.
To bypass that system
OR to use a newer /6 in an older car (say a ’66 A-body), a person will need to block that port.
On small blocks. From (I think) ’74, until replaced by the Magnums, the system is different.
First the cylinder heads have a taller exhaust manifold flange. Below the exhaust port, there is a ¼“ hole drilled at an angle onto the exhaust port (on cylinder head).
The one bottom picture, I suspect the A.I.R. ports have been plugged and painted over.
On the exhaust manifold, there is a channel cast into it with ports on both ends. The front side of the manifolds have a pipe plug screwed into it (which I do not have its measurements with me at the moment).
The back side of both have a similar flange but no pipe plug. This one will have a bolt hole on top. Either the Aspirator tube or A.I.R. tube/pipe bolts to (like the plug picture, above).
The problem with small blocks is if you install an older engine into a newer car, the Aspirator/A.I.R. pipe is not doing anything and can thereby be removed.
If you install a newer engine into an older car OR install headers onto a ’74 (or whatever year it might be) up engine – those ¼” drilled holes will need to be plugged.
A person can get 8 (or more if you are prong on losing them) ¼” plugs (they will use an Allen wrench to install). Also get a ¼” tap for the pipe plugs. I might be wrong, but I think the pipe threads are different than what normal ¼” bolts use. Just make sure the plugs are screwed into head enough so they are recessed and will not touch the exhaust manifold (or header).
A person can also use this method on a small block FMJ vehicle and remove the Aspirator/A.I.R. pipe(s) and can leave the rear exhaust manifold ports unplugged.
However, I think plugging both (or single) rear exhaust manifold port(s) is fastest/least labor involved.
Big blocks are the easiest ones to convert. The cylinder heads are the same – only the exhaust manifolds are different. Just get a pair of older exhaust manifolds and you are done.
Even better, get a pair of late ‘60’s to early ‘70’s HiPo manifolds (or headers) for even more flow.
If plugging the small block manifold (or /6 head port), you have 3 options:
If your old Aspirator pipes are not “too rusty” and yon can make a cap, by cutting the tubing about 1-1/2” or so, out and then crimp off the end (a hammer or a vise does a nice job). I prefer to fold the crimp myself – but one has a few options. If not folded, then you will need to weld (or whatever) the seam - so there are no leaks.
Example:
Note: I didn't do this one. I would cut pipe a bit father out, for this short is "too short" to do things.
Note: If pipes are not rusted too badly, there are people looking for these in emission states - so think about others, before cutting!
OR, find a OEM plug/plate (not easy to do), or make your own plate.
I have purchased some metal stock to make some plates as well as gasket material to make gaskets with – but hadn’t done so yet. Also, my garage is WAY TOO COLD to be out in it making some, until spring time.
The last picture is "make your own header gasket" material
OR, purchase a suitable pipe plug and tap. Tap threads into your existing hole and insert pipe plug.
I have pictures, but can't find them, at the moment.
More thoughts on other systems, in a bit.
BudW
