1966 L36 Vacuum advance Mechanism

[Ronald L.]

The 1966 427/390 HP uses Vac Can with 355 stamped in it.

Is there an accurate reproduction - that "functions" as intended???

[Wayne M.]

Re: 1966 L36 Vacuum advance Mechanism

The 1966 427/390 HP uses Vac Can with 355 stamped in it.

Is there an accurate reproduction - that "functions" as intended???

Ron here's the Delco spec's; this might help in selecting a 'B' series can.

1115355: "Hg to start advance 5 to 7; "Hg for max advance 11.2 to 12.7; maximum distributor advance = 8 distr. degrees (ie. 16 @ crank).

I'm guessing that your original can is stamped MS 355_16 (or 15).

[Terry D.]

Re: 1966 L36 Vacuum advance Mechanism

Ron
Google "Lars Grimsrud or chevy vacuum advance and you will find specs on all chevy advance cans as well as cross references to part numbers.
Terry

[John D.]

Re: 1966 L36 Vacuum advance Mechanism

Is there an accurate repro you ask. Highly unlikely.
NOS box reads D1382 and as mentioned 1115355. Can is stamped MS
355 15.
Don't know if NAPA sells a Standard with specs that will work.
Now the B28-replacement for 236-16 (hard to find except maybe thru GM) for the 30-30 may work. Duke knows all this stuff but is probably tired repeating it.

[Joe R.]

Re: 1966 L36 Vacuum advance Mechanism

Ron,

Here's a good thread on vacuum advance cans:

https://www.forums.ncrs.org/showthre...=2667&uid=9299

Joe

[Duke W.]

Re: 1966 L36 Vacuum advance Mechanism

The 1966 427/390 HP uses Vac Can with 355 stamped in it.

Is there an accurate reproduction - that "functions" as intended???

I gave the answer in the last thread on this subject a day to two ago.

Duke

[Ronald L.]

Re: 1966 L36 Vacuum advance Mechanism

Duke - that was probaly between the time I put this same info to a Vac can thread - that had no reply since the weekend and today, sorry, since you did not see that one, a blown vac can and pwer valve seem to be clearly implicated in the "breaking down" troubles I've noted.

The simple vac can test - is suck on the hose, if you pull air, the can is blown.

Without verifying the vac can the engine RPM responds like you just left the vac port uncapped, idle speed jumps up, so does timing - but you never get the full effect.

I have seen the basic vac can threads.

They don't discuss the currently available 'exact reproduction' parts available from Michigan based Big Box Corvette Stores and owners experience, performance, testing etc.

That was the basic input I was looking for - are these exact reproductions - any good???

[Duke W.]

Re: 1966 L36 Vacuum advance Mechanism

There have been mixed reports on "reproduction" VACs. Some may have a "correct" number, but may not meet the specs for that number.

The VAC is worth two originality points and one condition point, so just buying a proper B-number VAC is a one point deduction for originality.

Pulling a vacuum on the VAC alone is not a complete test. One failure mode is seizing. The VAC holds vacuum, but does not move.

With a Mighty Vac and timing light you can verify that the VAC is both functional and meets spec, and I highly recommend testing new VACs regardless of the purchase source.

The VAC is a simple and inexpensive device, but having one that is functional and correctly matched to the engine's manifold vacuum characteristics is critical to good engine operation.

Duke

[Stuart F.]

Re: 1966 L36 Vacuum advance Mechanism

Why not give it a shot and then "test and verify". That's what I had to do some time back. I ordered from several sources only to find they did not meet spec - except for how they were stamped. If you only want the correct stamp and not the correct performance, you're good to go.

Stu Fox

[Ronald L.]

Re: 1966 L36 Vacuum advance Mechanism

Stu, I had the same problem with thermostats stamped 180 that opened at 200 degrees.

In this regard, installation to test is a bit more complicated.

One question though on the comment on judging appearance - if it was an exact reproduction - how can you tell that it is, if it is exact?

[Stuart F.]

Re: 1966 L36 Vacuum advance Mechanism

Ron;

I hope Duke's latest post answers your question as he said it best. Make sure that, whatever you buy from whatever source, they have a good return policy. Most of the parts houses buy from another source and do not test themselves, so if you get one out of spec you'll want to be able to return it for a refund or credit as any replacements they may offer are just as bad. If you don't call it to their attention emphatically, they won't take the matter up with their supplier to correct their quality. But then you already know all this I'm sure.

Stu Fox

[Ronald L.]

Re: 1966 L36 Vacuum advance Mechanism

I found the Duke-Lar's PDF and this gets to the basics and resinforced where my concern was - it should be OK with the stated engine.

Now - on parts supply. As Duke indicates with the history of DANA, Standard Products...you can pretty much bet that the "entry-point of these parts into the Corvette world" has asked SP to make these correct reproductions.

And yes, that return guarantee is important to have in hand. That in part is why I will get the part from a supplier that has been very good with my business, had parts in stock (novel concept) and is good where there is a problem - parts that do not meet intended specs. Vac and temp are both key and easily measured, aren't they?

[Joe L.]

Re: 1966 L36 Vacuum advance Mechanism

The 1966 427/390 HP uses Vac Can with 355 stamped in it.

Is there an accurate reproduction - that "functions" as intended???

Ronald-----

As far as the "reproductions" go, I don't know how well they perform. The '355' is one of the few that are "reproduced" per original configuration and stampings. I would be concerned about original performance, though. Many reproduction parts focus much more on configuration than "original quality" and "original performance". I don't know who makes these reproductions.

As far as REPLACEMENT vacuum controls go, any with a stamping of "B20" or "B26" are equivalent to the original GM #1115355. These can be purchased under NAPA/Echlin #VC1765, Standard Motor Parts VC-181, GM #88924983, or Delco # D1310C. All are EXACTLY the same piece as manufactured by Standard Motor Products.

So, how do these perform? Well, I expect that Standard Motor Products knows something about making these things. They've been making them for about as long as Delco-Remy did. In fact, longer, since Delco-Remy quit making them about 1990 whereas Standard has continued right up to the present. Might some of these be off-spec as to performance? Yes, but so might some of the original GM #1115355's when Delco-Remy was still making them.

[Ronald L.]

Re: 1966 L36 Vacuum advance Mechanism

Duke & Joe,

New part on the car, I have vac advance! Worked like a charm.
24* mechanical and what this vac adv adds we end up with about 38 - 40* total at the crank.

Ran better than I can remember on the outbound, but after a short hot soak and up to its favorite 210* it showed some of its sputtering, but nothing like before.

I tested the original unit, zero pull on the vac machine.

[Duke W.]

Re: 1966 L36 Vacuum advance Mechanism

...glad it worked out, but I don't thing you understand the spark advance "map".

It's controlled by two independent variables - engine revs and manifold vacuum.

If you plot it on a XYZ scale you get a surface, and the entire surface can be moved up and down by changing the initial advance.

There are essentially an infinite number of spark advance values depending on speed and load as represented by manifold vacuum, but to simplify things a bit, we can discuss THREE total timing figures.

1. Total WOT advance, which is the sum of initial and full centrifugal, which is (OE) 30@ 5000 for you engine, so if initial is set at 8, total WOT achieves 38 at 5000.

2. Total idle advance, which is usually the sum of initial and full vacuum advance, but might add a few degrees of centrifugal if it's a SHP engine that idles higher than the start of the centrifugal curve.

3. Total cruise advance, which is the sum of initial, centrigual based on the cruise RPM, and vacuum advance based on manifold vacuum. Some SHP engines that have aggressive centrifugal curves that max out early can cruise at the sum of initial, full centrifugal, and full vacuum advance, which can be as high as low to mid 50s degrees.

Duke