Correct number 67 L79 vacuum advance can?

[Mike E.]

The JG is rather non-specific on this. What are the original stamped numbers/code on a 67 L79 vacuum advance unit. Or at least, what is on your car if you believe it is original?

[Richard M.]

Re: Correct number 67 L79 vacuum advance can?

Mike, The AMA spec has a chart on page 41 of the PDF with specs for all HP ratings. I coincidentally just had to verify which vacuum advance was stock for a 435hp.

Spec is at:
gmheritagecenter.com and go to Archive....Vehicle Information kits.....download the 1967 kit.

The chart does not give part numbers, but from the specs it can be devised with some help from some of the part number references I recall.

I see the L79 spec shows it begins at 4"/Hg, all in at 7", with a max of 16* advance. IIRC that's a MS 236 16 on top of the mount tab on the can. Pt# 1116236, Delco D1316A in Gr 2.410.

[Duke W.]

Re: Correct number 67 L79 vacuum advance can?

MS 236 16 is correct, however, it's not a good match for the L-79 idle manifold vacuum. The L-79 spark advance map is rather strange. I combines the long, lazy centrifugal curve of the 300 HP engine with the very aggressive VAC from the 30-30 cam engine. It should have a shorter (say about 26-27 degrees), quicker centrifugal and a less aggressive 12" VAC (B26 current replacement).

Details are in a thread I started in Dec. 2012 - L-79 distributor blueprint overhaul.

The VAC is only worth 3 points - two for originality and one for condition. If the engine has the "wrong" VAC as far as the number is concerned, I take one originality point, which is not much of a price to pay for an optimized spark advance map that will improve performance, especially low end torque.

Duke

[Mike E.]

Re: Correct number 67 L79 vacuum advance can?

Thanks to both of you for you input!

[William F.]

Re: Correct number 67 L79 vacuum advance can?

Surely original vac advance wasn't all in at 7" when these L79

Surely factory L79 vac wasn't all in at 7" Hg when these engines usually give at least 14" manifold vac at idle???

[Richard M.]

Re: Correct number 67 L79 vacuum advance can?

Surely original vac advance wasn't all in at 7" when these L79

Surely factory L79 vac wasn't all in at 7" Hg when these engines usually give at least 14" manifold vac at idle???

Here you go......Why? I do not know.

P1170061.jpgP1170062.jpg

[Richard M.]

Re: Correct number 67 L79 vacuum advance can?

While I had the vac pump out, I tested 2 MS 201 15's. Should be all in at 15"/Hg. First one came off a running driving L71, other is a new reproduction I just got in.

Old unit from L71... 1st pic "starts@", 2nd pic 1/2 in, 3rd pic, all in. Nice isn't it?
P1170057.jpgP1170058.jpgP1170059.jpg

Repro.....2nd pic "starts@"...almost 14, 3rd pic all in...at 21". I think they got their "strts@" and their all-in specs wrong.
P1170060.jpgP1170061.jpgP1170062.jpg

Both junk.