C2: 427 A.I.R. intake bypass fitting for '66

[Dan Pepper]

I have a '66 L36 with AC and AIR and am trying to find the right intake bypass hose fitting. These came from the factory with elbow-type bypass fittings (like 350hp 327's) and a "U" shaped bypass hose from intake to waterpump. The 427 uses the same set-up as to allow clearance for the smog pump to pivot so the belt can be adjusted.

I have been told that the intake used a pressed-in bypass elbow fitting, but my car (I believe original manifold) has a threaded hole. The car came with a straight threaded fitting, 13/16 OD on the threads. I suppose someone could have threaded the hole, but think is highly unlikely.

Question: Should this fitting be pressed in or threaded? And if threaded, is this the corrct dia?

Thanks in advance.

[Joe L.]

Re: C2: 427 A.I.R. intake bypass fitting for '66

Dan-----

It's my belief and observation that the GM #3866948 intake manifold used a pressed-in type bypass fitting. That was also the case for '284' waterpumps. However, I would not rule out the possibility that threaded type fitiings were used. I've never seen this on a '284' waterpump and I can't really say that I've ever seen it on a '948' manifold, either. However, I have not looked at a huge number of these manifolds.

In any event, you mention that your manifold has a STRAIGHT threaded fitting. I believe that the fittings for cars with AIR were both 90 degree bends. So, I don't understand how the striagt fitting could have been original to an AIR application even if the threads are original.

Your 13/16" OD dimension for the fitting is approximately the size of 1/2" National Pipe Thread (NPT) which is the size that these manifold fittings are when threaded. However, it's also likely the size that would be used if a pressed-in fitting were converted to threaded. I'm not even 100% sure if this can be done on these manifolds, though, as I've never done it.

[Mike M.]

Re: C2: 427 A.I.R. intake bypass fitting for '66

the elboe presses into the intake on our 67 n435 K-19. did a good bit of research on the smog systems when i restored the coupe in the mid-90's. the 90 degreee elboe isn't radiused but rather is a sharp 90 degree angle, soldered two piece elboe as i recall. check out the 67 judging manual(which i don't have handy) and i believe there is a good description therein. mike

[Dan Pepper]

Re: C2: 427 A.I.R. intake bypass fitting for '66

Regardless, the manifold is now tapped for threads - it must be the 1/2 NPT thread as you mentioned, Joe. Do you guys suspect this is the same size and config as the 327 bypass elbow? I had Art Gould rebuild the H20 pump with the correct press-type fitting, and would like the fittings to be the same if not look similar. I suppose any threaded unit will have an octagon shoulder so it can be threaded into place.