#201 Vacuum Advance Can

[Peter S.]

Is there any difference between the vacuum advance can on a non-TI '69 350/350 and a TI 350/350? I ask because Zip and Paragon both list the #201 for the '69 350/350, but Zip also lists a #355 for the '69 350hp model, and Paragon list a #360 for a '69 350hp and also a "B" unit for 1969 350 w/T.I.

Naturally the first one I clicked was the #201 model, purchased and installed this afternoon. I am comforted that the old can is a #201 with "MS" above it and a "15" beside it.

Also, I see no mention in the TIM&JG about judging the vacuum advance cans and their numbers. Any way to decipher them?

[Duke W.]

Re: #201 Vacuum Advance Can

I'm not aware that any engine configurations had a different spark advance map setup depending on whether they were TI or single point.

Chances are what you bought is just a stamped generic VAC that does not meet the 201 spec, however, according to the AMA specs that you can download from the GM Heritage Web site, the '69 L-46 VAC specs correspond to a 360 12. The specs are also listed in the CSM

Many of these "reproduction" VACs that have proper numbers stamped are not even close to the correct spec for the stamped number, so measure the start and end points for what you have and post.


Duke

[Joe L.]

Re: #201 Vacuum Advance Can

Is there any difference between the vacuum advance can on a non-TI '69 350/350 and a TI 350/350? I ask because Zip and Paragon both list the #201 for the '69 350/350, but Zip also lists a #355 for the '69 350hp model, and Paragon list a #360 for a '69 350hp and also a "B" unit for 1969 350 w/T.I.

Naturally the first one I clicked was the #201 model, purchased and installed this afternoon. I am comforted that the old can is a #201 with "MS" above it and a "15" beside it.

Also, I see no mention in the TIM&JG about judging the vacuum advance cans and their numbers. Any way to decipher them?

Peter-----


Well, there is conflicting information on this. However, I feel pretty sure that the 1969 with L-46 and standard ignition used the GM #1115360 while the L-46 with TI used the GM #1116201.

Deciphering the code on these vacuum controls is easy. The 3 digit series represents the last 3 digits of the GM part number. The two digit series represents the maximum number of degrees advance the control will produce.

[Richard M.]

Re: #201 Vacuum Advance Can

Just some words of caution.....a few years ago I bought a repro MS201 and when I tested it using my MityVac and 2 different vacuum gauges, the specs were far off from the original specs. It was all in at 19", not 15"!

It looked pretty with all the right numbers but they missed the functionality! I returned that POS. Whatever you buy, best to test it before installation.

Even if something isn't in the JG, that doesn't mean it is not checked. It can't have everything. However, IMHO, I'd prefer a passing OPs test and better running engine over a few micropoints taken off for wrong numbers on a vacuum advance.

More info,

Here...
https://www.forums.ncrs.org/showthre...024#post537024

And here....
https://www.forums.ncrs.org/showthre...050#post537050

full thread....here

Rich

[Peter S.]

Re: #201 Vacuum Advance Can

I appreciate the responses. Corvette night is one night a week, so I will test next week and post the results. I am a bit discouraged hearing about Rich's experiences, and the fact that I already installed the new unit.

Joe, thank you for confirming the part numbers. My old unit appears fairly original and confirms that the L46 w/ TI had the 1116201 unit.

Peter

[William C.]

Re: #201 Vacuum Advance Can

If you have a mityvac, you can test it in the garage. The spec not stamped into the flange is the inches of vacuum to achieve full advance, VERY important if you have a high perf engine. I've got the specs for all GM vacuum advance distributors from 1959-1969, if you need a particular Number specs drop me an email, too many pages to post here, as all GM distributors are batched in one list.

[Timothy B.]

Re: #201 Vacuum Advance Can

Peter,

Why can't you clean the old #210 control and reuse, if it's the original and in working order it's you best bet.

[Duke W.]

Re: #201 Vacuum Advance Can

Just some words of caution.....a few years ago I bought a repro MS201 and when I tested it using my MityVac and 2 different vacuum gauges, the specs were far off from the original specs. It was all in at 19", not 15"!It looked pretty with all the right numbers but they missed the functionality! I returned that POS. Whatever you buy, best to test it before installation.Even if something isn't in the JG, that doesn't mean it is not checked. It can't have everything. However, IMHO, I'd prefer a passing OPs test and better running engine over a few micropoints taken off for wrong numbers on a vacuum advance.

The VAC is worth a total of three points - two for originality and one for condition. Some of the JGs specify the stamped number, some don't.If the OE VAC is really knarly looking with surface rust you lose the condition point.

If it has a B-number instead correct OE number you lose (maybe) one originality point for "OE replacement". You can't always see the number with the dist. cap installed, and removal is not required.It's certainly worth one point to have a functioning VAC that is matched to your engine, i.e. meets the Two-Inch Rule.

Some OE non-emission engines don't - like '63 L-76 and L-78, and most ported advance application will require a different VAC if they are converted to full time, and there are only three that will meet the requirements of any OE engine. This simple ten-dollar part is absolutely critical to good engine performance and fuel economy in normal road driving.It's all explained in the San Diego presentation.

http://www.metroli.org/pdf/2012 Nationals tuningseminar.pdf

Duke

[Michael H.]

Re: #201 Vacuum Advance Can

I'm not aware that any engine configurations had a different spark advance map setup depending on whether they were TI or single point.



Duke

Duke,

I think some engines with TI do have a different advance map than the same engine without TI. I sent you a chart of all TI distributors a few years ago. Compare some of the data to distributors for the same engine without TI.

I don't know why TI would be different but but is, at least for some applications.

[Duke W.]

Re: #201 Vacuum Advance Can

I don't remember the chart, but can you list any specific examples?

I have the AMA specs for all years on my computer, and I refer to them when I need to know the OE spark advance map, and I don't recall ever seeing any difference between single point and TI on the same engine.

I am aware that the TI system results in a couple of degrees less advance at high revs than a single point with the same centrifugal curve and initial timing.

Duke

[Michael H.]

Re: #201 Vacuum Advance Can

I don't remember the chart, but can you list any specific examples?


Duke

I'll try to dig it out later today or this evening.

The 66 and 67 service manuals show the distributor specs too.

[Peter S.]

Re: #201 Vacuum Advance Can

Hi Tim,

Unfortunately I did not have a mityvac (now in hand) to test and figured there would be no issues with a replacement. Detonation symptoms point to my vacuum advance can. I now see that a mityvac is $10-20 more than the unit, I could have potentially saved myself money if I find out the old unit is just fine.

Peter

[Duke W.]

Re: #201 Vacuum Advance Can

Hi Tim,

Detonation symptoms point to my vacuum advance can.
Peter

I strongly disagree, and once you read and understand the San Diego presentation, you should too.

ANY new VAC should be tested with a MityVac for conformance to the specified start and stop points prior to installatinon, regardless of the source. After installation total advance should also be checked with a dial-back timing light.

You can never be too good looking, have too much money, or do too much testing.

Duke

[Peter S.]

Re: #201 Vacuum Advance Can

I strongly disagree, and once you read and understand the San Diego presentation, you should too.

ANY new VAC should be tested with a MityVac for conformance to the specified start and stop points prior to installatinon, regardless of the source. After installation total advance should also be checked with a dial-back timing light.

You can never be too good looking, have too much money, or do too much testing.

Duke

With all due respect Duke, what do you strongly disagree with?

Peter

[Duke W.]

Re: #201 Vacuum Advance Can

With your statement that I quoted in my post. That's why I quoted it.

Duke