Drilling A.I.R. Holes? y/n

[Brandon Metzger]

I have a '72 BB. From my understanding all BB came with A.I.R. I have two correct casting numbered exhaust manifolds, dated '70--date codes not judged on manifolds. Now the Rt exaust manifolt has the correct casting number but is a GM1T not a GM2T. I believe the 1 is without AIR and the 2 is with AIR. I am trying to get a correct GM2T with correct casting numbers.

Now for the question, on the right, did this manifold come in a GM2T version or not? From reading a thread titled C3--Big Block exhaust manifold, Joe Lucia on oct. 30 posted that the left had two part number one for AIR one without and the Rt was just 3888028. If the Rt side numbers did not change is it advisable or not to drill the AIR holes into the manifold I have now? I don't know if this is possible or if it would be obvious that I did it instead of the factory.

I made a number of statements that if they are wrong please correct me.

Thank you,
Brandon

[Joe L.]

Re: Drilling A.I.R. Holes? y/n

Brandon-----

The "GM1" and "GM2" represent pattern numbers. They have nothing to do, whatsoever, with the presence or absence of AIR fittings in the manifolds. They are just the "luck of the draw" and have no real meaning from a restoration or originality standpoint. The only way you could know what the pattern numbers were for the manifolds originally installed on your car would be to have those original manifolds. The pattern number does not necessarily "match" from side-to-side. In the first place, the manifolds are different and in the second place the pattern number is independent of anything else.

All 1972 with LS-5 did use AIR. If you have a manifold that is not drilled and tapped for AIR, then it's a replacement manifold and not the original used on the car.

I don't consider it practical for a hobbyist to attempt to drill and tap the manifolds for AIR. Some machine shops might attempt it, but I doubt that you'd find too many that would take the job. Of those that might take it, how many would get it right could be a small number.

[Brandon Metzger]

Re: Drilling A.I.R. Holes? y/n

Wonderful Joe. Thank you much. I was hoping you would catch this post.

On the your earlier post on manifolds you metioned that the GM #3969869 "was also manufactured into TWO finished PART number for AIR and non-AIR applications". What do you mean by two finished part numbers? Should I be looking for something other than the 3969869 number, since I obviously need the AIR manifolds.

I am looking at this item on EBay and believe it to be correct for my application. Item number 8011502716.

Regards,
Brandon

[Harmon C.]

Re: Drilling A.I.R. Holes? y/n

Brandon

To add to what Joe said the holes had a step in the bottom to keep the metal tube in position. The four tubes never line up that great and would be very hard to do one at a time.
Lyle

[Harmon C.]

Re: Drilling A.I.R. Holes? y/n

Brandon
I see no AIR holes in that manifold on EBay.
Lyle.

[Brandon Metzger]

Re: Drilling A.I.R. Holes? y/n

Great point. I would not have thought of that till after the attempt. Thank God for this board, it has saved me many a time.

Great to hear from you Lyle, this is Brandon in Ypsilanti, MI. You did my belts...Oh about a year and a half ago. Hope all is well. I tell everyone the "upgrade" to show quality belts was the most expencive $150 I ever spent because everything else that has followed has needed to be "correct". Your results were great and I can't wait till they are being used, my project has turned into a frame off not just an interior make over.

Regards,
Brandon

[Brandon Metzger]

Re: Drilling A.I.R. Holes? y/n

The item number is 8011502716. In the item I am looking at it does look like it has the holes and states it in the discription. Should be a Sep. 27, 1971 dated manifold.

Brandon

[Joe L.]

Re: Drilling A.I.R. Holes? y/n

Brandon-----

The manifold in the eBay auction item is the type with drilled and tapped AIR fittings. The fittings have been "plugged", however. Usually, these plugs can be relatively easily removed, although, sometimes, the application of heat to the surrounding area may be required.

The original 70-74 left side manifold, casting GM #3969869, was manufactured into 2 finished manifolds. One was GM #3969869 (same as the casting number). This manifold did not have drilled and tapped AIR fittings. It was used for 70-71 LS-5. The other was GM #3969923. This manifold had drilled and tapped AIR fittings. The finished part number DOES NOT appear anywhere on the manifold (except, of course, in those cases in which the casting number and finished part number for the piece are the same).

[Brandon Metzger]

Re: Drilling A.I.R. Holes? y/n

Joe,
I take it the drilled and tapped air fittings is done by GM not some shop on the street. I am also understanding that the manifold on the eBay auction would be "correct for my car and would fit the AIR system once the "plugs" were removed.

Thank you again,
Brandon

Your patients and willingness to teach is appreciated

[Joe L.]

Re: Drilling A.I.R. Holes? y/n

Brandon------

Yes, the AIR fittings were drilled and tapped by GM at the plant that did the finish machining of the manifolds. Most likely, this was the Tonawanda engine plant. As I mentioned, I think that most machine shops would have difficulty doing this and it might cost more than just buying the correct manifold in the first place.

This manifold in the eBay auction would be correct for your car with respect to configuration, casting number, and AIR fittings.

[Brandon Metzger]

Thank you Joe, much appriciated! *NM*

[Terry F.]

Re: Thank you Joe, much appriciated!

I believe the threads are totally not standard threads. I remember looking at them closely and they had a steep pitch to them and were unusually coarse. Unless a machine shop ordered special tooling (expensive) the job would probably turn out incorrect. Just my words of caution, Terry

[John L.]

Re: Drilling A.I.R. Holes? y/n.....No Need To

Brandon,
I have a set of BB Exhaust Manifolds W/ Air (Plugged) off of my 71. They are not original to my 71. It had a set of Hooker headers on it when I got it in 1999 and I could only find manifolds w/air at that time. I have run them about 1500 miles since installing them. If you are interested in a swap or something send me a e-mail at jliner@dovecommuication.com. They are in great shape, I'm getting ready to pull them off in a month or so to do some head work so they would be available then. Send me a e-mail and we can talk. Best Regards,
John Liner NCRS 28230