ranger725

What is the correct plug for a '66 BB exhaust manifold with A.I.R. holes? I've seen plugs with a square end for tightening as well as plugs with hex key indents that are more flush with the manifold. I'm not running an air pump so I need to plug the holes.

Nowhere Man

There is no such thing as correct plugs. Non CA cars just got manifolds with no fittings. If I was you I would save the old mainfolds and buy new repros without the holes.

Vet65te

This question came up about a year ago on the NCRS Tech Forum. It caught my attention because when I get around to adding the 427 to my 65 Smallblock Coupe, I'll probably buy the Dorman repro's and they are the types with the A.I.R. holes. Most guys have used the pipe thread plugs in the past but they only reach a couple of the threads. JohnZ replied with this...They're 1/4"-18 NPSF (National Straight Pipe Thread). At the time, some folks thought that Grainger might be able to supply them but I was unable to dig up a listing for the NSPF plugs. The pic used for the Dorman replacements shows plugs in place but not sure which ones they are.
Mike T - Prescott AZ

ranger725

My car has the original manifolds with holes (plugged) and and no a.i.r. It was sold to a dealer in Montana. It had the square pipe plugs which I removed when I was restoring them. Both LI Corvette and Paragon sell the plugs, but they are the hex set screw type. It would seem to me that there were non-California cars built with a.i.r. plugged hole manifolds.

ranger725

Thanks, I saw those. I just wonder why LI Corvette and Paragon are selling the hex set screw type plugs. I inquired but haven't been able to get an answer.

MikeM

If the engine was an A.I.R. model, the manifolds were machined to accept the air tubes. If it was non A.I.R., the same manifolds didn't have the embossments machined for the bore step and threads. Maybe not all cases but some/many cases.

So if you're implying the factory plugged the non A.I.R. engines, the answer is no.

Mike67nv

I agree.

In all my years at the Fremont plant, I don’t recall every seeing a K19 (Air Injection Reactor) Chevy engine (small block or big block) go out the door with plugs in the manifold.

Specific engines codes destined to have K19 installed were the only engines to get drilled manifolds – there were other engine differences like distributors, timing etc. The manifolds, plugs and small air tubes inside the manifold were installed at the engine plant. Assembly plants removed the manifold plugs before the manifold air pipes were installed.

All of the plugs I remember were hex head, but any one plugging a K19 exhaust manifold couldn’t be too concerned about originality.