Source/Specs on Vacuum Cans

[John M.]

Re: Source/Specs on Vacuum Cans

I have an original 236 15 and a 355 16 One's out of a 66 L79 and the other a 67 327-300. I tested them both and they come "close" to the specs in the 67 service manual. I may have mixed those nubers up here, memory problem, but I'm sure the actual numbers are correct for the two applications and will confirm if needed.
John McRae 30025

[John L.]

Re: Vacuum Advance Control, VAC, specifications; how to select a VAC

Is the vacuum hose off of a 67/68 427 tripower car the same size as the 66 427/425 choke cutoff line. It looks like it is to me. I want to use a Tee off the later engine to go to manifold vacuum with my VC1810. My local NAPA store does not have a clue as to what size Tee I actually need even though I brought them an actual piece of vacuum hose. They gave me a tee (3/32) from a modern car vacuum system which seems too small to me. The engine has been running fine with the VC1810 and the stock ported vacuum. I am just doing some experimenting. When I first heard that the VC1810 was being discontinued, I went to the same NAPA store that I bought the others from and they were able to order it and it arrived in two days.

[Duke W.]

Re: Source/Specs on Vacuum Cans

Anybody have any idea what the "B" number stamped on the cans means?

Reason I ask is that NAPA and Standard both show pictures of one of the cans on their respective websites. You can find pictures of the NAPA VC176 and the Standard VC-181 on their respective websites. However on both of the pictures, you can see that they are both stamped "B26", and not "B20" as Duke lists in his posting.

In the past there was a NAPA/Echlin VC1808, stamped "B26" that had the same specs as the VC1765 stamped "B20". My understanding is that the NAPA part numbers were consolidated to VC1765, and I expect the same was done with the other brands.

So a B26 should measure the same as a B20, but alway check! Tolerance of +/- 1" Hg, and 1-2 degrees advance is okay. You can measure the start and end points of the rod pull with a Mighty Vac, and if it's okay, check the actual advance after it's installed or on a distributor test machine. If the start and end pull points meet the vacuum specs, the advance is probably okay.

The B-number has been used by Standard Motor Products to ID the various VACs over the years. AFAIK the other brands manufactured their own parts in the distant past, and may have had their own ID schemes, but as they were bought by Standard, manufacturing was consolidated using the Standard ID system, but the various brand names remain and are used for different marketing channels.

Standard's most recent acquisition, a couple of years ago, was the Dana Controls Division, which included the Echlin brand.

Duke

[Duke W.]

Re: Vacuum Advance Control, VAC, specifications; how to select a VAC

Is the vacuum hose off of a 67/68 427 tripower car the same size as the 66 427/425 choke cutoff line. It looks like it is to me. I want to use a Tee off the later engine to go to manifold vacuum with my VC1810. My local NAPA store does not have a clue as to what size Tee I actually need even though I brought them an actual piece of vacuum hose. They gave me a tee (3/32) from a modern car vacuum system which seems too small to me. The engine has been running fine with the VC1810 and the stock ported vacuum. I am just doing some experimenting. When I first heard that the VC1810 was being discontinued, I went to the same NAPA store that I bought the others from and they were able to order it and it arrived in two days.

Most vintage VAC signal hoses are 1/8", and you should be able to find 1/8" tee. Try an auto parts store that carries the Help! product line of packaged small hardware.

If you have the OE cam a VC1765 should be the best fit since the engine should pull about 14" @ 900. If you have a cam with more overlap that pulls less than 14", then the VC1820 is the way to go.

If you're handy, you can make the change on a L-72 or L-71 that's undetectable. It requires moving the vacuum advance port to below the throttle plate by plugging an existing hole with a small piece of lead shot or epoxy and then drilling a small hole - tough to explain, but you should be able to figure it out by looking at how the vacuum advance signal port is configured on the carb. With this modification the OE vacuum hose routing is unchanged, but you have full time, not ported advance.

Using a 1/8" tee and a couple of feet of 1/8" hose to fabricate a new harness for the choke vacuum break and vacuum advance is a cheap way test the modification.

Duke

[Stuart F.]

Re: Source/Specs on Vacuum Cans

I don't know if this would be applicable with a Holley or a Carter, but I used to modify the vacuum port in old QJ's from inside the throttle bore. Typically, the vacuum slot at the butterfly was above the butterfly at idle and was exposed only as you opened the throttle. It was simple to notch the opening so it was fully or at least partially exposed below the butterfly at idle. Just a little file or dremel work was all that was required. Then, everything looks perfectly stock outside the carburetor.

Stu Fox

[Duke W.]

Re: Source/Specs on Vacuum Cans

I hope you didn't confuse the off-idle fuel transfer slots with the vacuum advance port. I'm not intimately familiar with Q-jets, but a "ported" vacuum advance port is usually a small hole just above the throttle valves when they are in the idle range of throttle stop adjustment.

Duke

[Stuart F.]

Re: Source/Specs on Vacuum Cans

Oh! No No Duke. I may not be the brightest bulb in the room, but I like to think that what I lack in mechanical engineering expertise, I make up with a little bit of good old American common sense. This was back in the early emission controls days when we were all out to beat the system, so to speak. My first test case was a 72 Nova SS w/ 350 Automatic.

The vacuum port in the throttle bore was a vertical slot, but w/i the casting there was a chamber of sorts behind it which opened up well below the butterfly position allowing one to slot or open up the port below the butterfly. It was easy to trace, which I probably did with a thin wire to be certain. I know I always checked the port for full vacuum afterwards.

In later years, when we had emissions testing to endure, I used the vacuum control solenoid from the 72 with a manual switch to control such things a vacuum signal to EGR valves, etc., and I still have that sucker laying around on my parts shelf today.

Again, I'm not sure if such a procedure would be possible on a Carter or Holley, but I want to check into it. I just rehabed an AFB in my garage that I will look at.

Thanks for all your advice and critique. I appreciate it. I'm sort of from the old "back yard" mechanic school some times.

Stu Fox