Source/Specs on Vacuum Cans

[Joel T.]

Hi Guys;

I'm looking for specifications and a good supplier for vacuum cans for C2 distributors... Based upon Duke's "two inch rule", I think one really needs to know the specs of the can prior to installation , particularly if you are running a camshaft which is more aggressive than stock... Just popping in the "standard" for a particular motor may not do the trick...

I recently tried to pick up a second B28 can for my 1963/340 distributor rebuild from Napa... with no luck... they are telling me that not even the manufacturer has them! I can find what I think is the equivalent in the LI Corvette catalog but would rather know the specs before I plunk down $40.00 a pop...

Can anyone provide the specs for the following along with a decent supplier....

201

236

360

355

373


Thanks!! Joel

[Larry M.]

Re: Source/Specs on Vacuum Cans

Joel:

I recently had the same problem looking for a B28 vacuum can. I finally found one through ACDELCO/GM. Purchased from the local Chevrolet Dealer parts department. They had to order it for me. Numbers are Delco #D1312C, or GM #88924985. List cost $11.

The D1312C is the same spec as the B28, and has B28 on the can mounting arm. That spec is 16 degrees at approx 8" Hg vac , with advance beginning at approx 5" Hg vac.

The #236 OEM factory can has the following specifications from the 1967 Chevrolet Service Manual: 0 degrees advance at 4" Hg vac and 16 degrees advance at 7" Hg vac.

Don't know about the others.

Larry

[Duke W.]

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

Vacuum advance control, VAC, specifications; how to select a VAC

The "B28" (NAPA VC1810), which is equivalent to the OE 236 is also available in other brands as are the other VACs. All are the same Standard Motor Products manufactured parts and should have the same ID. (Note: I'm not absolutely sure about the Delco numbers, but it's the best I can decipher from their online catalog, which is confusing given all the recent part number changes.) Idle vacuums listed are in neutral with manual trans and Drive with auto trans. If idle vacuum is on one of the borders, a slight increase in idle speed will increase vacuum.

"B28" 0@4" 16@8" (idle vacuum less than 14")
NAPA VC1820
BWD (Borg Warner) V329
Standard VC-177
Niehoff DR305
Delco D1312C

"B20" 0@6" 16@12" (idle vacuum 14-17")
NAPA VC1765
BWD V375
Standard VC-181
Niehoff DR320
Delco D1310C

"B22" 0@8" 16@15" (idle vacuum greater than 17")
NAPA VC1802
BWD V325
Standard VC-171
Niehoff DR315
Delco D1308C

The above advance specs are crankshaft degrees. Some specs list distributor degrees, which are one-half crankshaft degrees. Some published specs may vary. Production tolerance and specs can vary about +/- 1" Hg. and +/- 1-2 degs. crankshaft advance.

All these brands have online catalogs and cross references, so double check! Another brand is Wells, but I don't have any data. How about if you do an Interent search and give us the Wells numbers?

One of the above will meet the needs of virtually all OE '57 to '74 engines with VAC distributors or non-VAC distributors replaced with VAC distributors or ported vacuum advance converted to full time as follows. If an aftermarket cam is installed, use the "Two-Inch Rule". There are many OE VACs that are literally within production tolerance of each other, and many service VACs were not the same as OE, but relatively close. This is the reason we can boil down the replacements to only the following three. Many application catalogs list the number of the "B1" VAC for base and some other engines. This VAC takes as much as 18" to fully deploy. Do not use it. It's totally useless for any full time vacuum advance application.

B22: with manual trans, all base SB and optional SB with base engine camshaft (283-245/250/275, 327-300)

B20; All big block (exc. L-88, ZL-1), L-79, L-46, L-82 with manual trans, all SB with auto trans, exc L-82

B28: All SB with mechanical lifter camshafts, L-82 with auto trans, L-88, ZL-1

The following (from memory) are the specs for the OE VACs you mentioned - just the maximum advance @ vacuum. Starting specs are similar to the similar spec VAC listed above.

201 - 15@15.5"
236 - 16@8"
360 - 12@12"
355 - 16@12"
373 - don't know

Duke

[Joel T.]

Re: Source/Specs on Vacuum Cans

Thanks Duke;

Great information, which I suspected you had. I have it all copied to my "archive".

Just for my own edification, for proper performance, we should be looking at manifold vacuum at idle to confirm that we have the correct can installed, particularly if a non-stock cam is employed...

Thanks,

Joel

[Duke W.]

Re: Source/Specs on Vacuum Cans

I don't know how else to explain it. I've stated the "Two-Inch-Rule" many times.

Note that the VACs/observed manifold vacuums specified in my previous post all meet the "Two-inch-rule" - the VAC should provide full advance at no less than 2" less than typical idle vacuum, and for auto trans applications it's the idle vacuum in Drive that must be used.

That's why I recommend the next most "aggressive" VAC for the same engine equipped with an auto trans compared to a manual. With an auto trans, idling in Drive yields less vacuum than the same engine with a manual trans idling in neutral.

For example a typical idle condition for a 327/300 is 500@18" in neutral. With an auto it's about 450-475 in Drive and looses 2-3" of manifold vacuum, so a 12" VAC is typically needed on a 327/300/PG to comply with the "Two-Inch Rule", but the 15" VAC is okay with a manual transmission.

As the general rule, use the least aggressive VAC that meets the "Two-Inch Rule." More aggressive than necessary can cause part throttle or transient throttle detonation. For example the L-79 OE VAC is the 8-incher, but they typically idle at 750@14", so a 12" VAC meets the rule and mitigates detonation.

A "less aggressive" VAC can lead to idle instability due to loss of total idle advance. This is the case with the OE 327/340 VAC. It requires 15.5" to pull to the limit, but the Duntov cam only pulls about 12" at 900 - doesn't meet the rule - so at idle the variation in manifold vacuum from the high overlap will cause loss of advance, which further reduces idle speed/vacuum, which further reduces total idle advance, which futher reduces idle speed vacuum and so on until the engine stalls. This was the case with my 327/340 until I installed a "236" VAC circa 1966. It just would not idle with any stability and consistency until I installed a VAC that was properly matched to the idle vacuum characteristic.

Duke

[Stuart F.]

Re: Source/Specs on Vacuum Cans

What quality can one expect from the #236 offered by Paragon? I've heard horror stories about bad repros out there that cause more trouble than they are worth. I always test my cans with a vacuum pump and gauge to be certain they are in the ball park. Of course, you have to depend on your eye or feel to check movement of the diaphram/rod.

Stu Fox

[Duke W.]

Re: Source/Specs on Vacuum Cans

I have heard anecdotal evidence that some "repro" VACs with the "correct" stamped ID are no where near close to the original spec for the particular OE VAC.

I highly recommend that all new or used VACs be tested for conformance with specifications.

As far as any particular vendor is concerned - ask them, but I would be as willing to take it on faith as any statement made by a used car salesmen. To most of these guys all VACs are the same except the numbers. Most don't understand the specs or why a 300 HP engine needs a different spec VAC than a SHP engine.

Always check the actual performance of VACs against spec before installing.

Duke

[Patrick H.]

Re: Source/Specs on Vacuum Cans

Always check the actual performance of VACs against spec before installing.

Duke

True.

I bought an Echlin unit last year that was way off from published specs. Thankfully my distributor rebuilder sold me an original can that was "right on."

[Joe L.]

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

Vacuum advance control, VAC, specifications; how to select a VAC

The "B28" (NAPA VC1810), which is equivalent to the OE 236 is also available in other brands as are the other VACs. All are the same Standard Motor Products manufactured parts and should have the same ID. (Note: I'm not absolutely sure about the Delco numbers, but it's the best I can decipher from their online catalog, which is confusing given all the recent part number changes.) Idle vacuums listed are in neutral with manual trans and Drive with auto trans. If idle vacuum is on one of the borders, a slight increase in idle speed will increase vacuum.

"B28" 0@4" 16@8" (idle vacuum less than 14")
NAPA VC1820
BWD (Borg Warner) V329
Standard VC-177
Niehoff DR305
Delco D1312C

"B20" 0@6" 16@12" (idle vacuum 14-17")
NAPA VC1765
BWD V375
Standard VC-181
Niehoff DR320
Delco D1310C

"B22" 0@8" 16@15" (idle vacuum greater than 17")
NAPA VC1802
BWD V325
Standard VC-171
Niehoff DR315
Delco D1308C

The above advance specs are crankshaft degrees. Some specs list distributor degrees, which are one-half crankshaft degrees. Some published specs may vary. Production tolerance and specs can vary about +/- 1" Hg. and +/- 1-2 degs. crankshaft advance.

All these brands have online catalogs and cross references, so double check! Another brand is Wells, but I don't have any data. How about if you do an Interent search and give us the Wells numbers?

One of the above will meet the needs of virtually all OE '57 to '74 engines with VAC distributors or non-VAC distributors replaced with VAC distributors or ported vacuum advance converted to full time as follows. If an aftermarket cam is installed, use the "Two-Inch Rule". There are many OE VACs that are literally within production tolerance of each other, and many service VACs were not the same as OE, but relatively close. This is the reason we can boil down the replacements to only the following three. Many application catalogs list the number of the "B1" VAC for base and some other engines. This VAC takes as much as 18" to fully deploy. Do not use it. It's totally useless for any full time vacuum advance application.

B22: with manual trans, all base SB and optional SB with base engine camshaft (283-245/250/275, 327-300)

B20; All big block (exc. L-88, ZL-1), L-79, L-46, L-82 with manual trans, all SB with auto trans, exc L-82

B28: All SB with mechanical lifter camshafts, L-82 with auto trans, L-88, ZL-1

The following (from memory) are the specs for the OE VACs you mentioned - just the maximum advance @ vacuum. Starting specs are similar to the similar spec VAC listed above.

201 - 15@15.5"
236 - 16@8"
360 - 12@12"
355 - 16@12"
373 - don't know

Duke

Duke and Joel-----


A GM #1115373, aka Delco D1355A, had "no specs". It was a "vacuum control" with no provisions for vacuum and was used on L-88/ZL-1 engines which had no vacuum advance. I think it was more of an "adapter" to allow a vacuum control type distributor housing and base plate to be used for a non-vacuum advance application.

[Stuart F.]

Re: Source/Specs on Vacuum Cans

Duke;

The reason I posted the question about the 236 can from Paragon is I had gotten one recently, but did not use because it tested (in my unscientific method using a vacuum pump w/gauge) as 0 dgrees @ 7" (beginning @ 8"), all in @ 12". This, of course would not meet the 2" rule for my 63 340 hp. I have old 57 vintage cans laying around that do that well (hex cans).

I don't like to fault Paragon as I have gotten some good stuff from them and some not so good stuff. I bought one of their oil filter canisters awhile back and used it for a couple of oil changes until I deceided it was not as robust as the original (which has twice the thickness) and was not as safe. A few years back I had to drop my oil pan to pound out a good size dent from an off road excursion years back (in my youth) so I'm a little paranoid. They told me at the winter meet that their dies can't draw the thickness of the original any more.

Thanks to your spec info though, I am now more able to make a good judgement on the vacuum can issue.

Stu Fox

[William C.]

Re: Source/Specs on Vacuum Cans

I have seen considerable variation in reproduction vacuum cans on my machine when tested, from "as advertised" to "way off" I can only say if you buy one, test it on a machine or with a hand held vacuum pump and go from there. "Consistantly inconsistant" seems to describe the variation.

[Joel T.]

Re: Source/Specs on Vacuum Cans

Hi Guys;

One last comment...

Finding any one of the aforementioned (B28 type) Vacuum Cans is becoming a challenge. I know that places like of LI Corvette and Paragon list reproduction parts however checking with the local auto parts places turns up dry most of the time. The websites for BWD, Niehoff, etc.. don't even list them...

I think I bought the last B28 Napa had a while back and looking around today the only can I could find was the Delco part number and the guy had only one... needless to say I bought it.

Guess what will be on my Carlisle shopping list this year......

BTW thanks to all who weighed in here.... I think we shared some really valuable information.. I know that I learned a few things!

Joel

[Duke W.]

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

Duke and Joel-----


A GM #1115373, aka Delco D1355A, had "no specs". It was a "vacuum control" with no provisions for vacuum and was used on L-88/ZL-1 engines which had no vacuum advance. I think it was more of an "adapter" to allow a vacuum control type distributor housing and base plate to be used for a non-vacuum advance application.

Joe - back when I was involved with the new '67 "12-mile-L-88" it had a conventional VAC, but the nipple was cut off so a hose could not be attached. I don't recall the ID number.

My Cosworth Vega was built without a VAC (It has one now,), and had a plastic "plate" in place of the VAC to hold the radial position of the pickup coil. It didn't protrude beyond the edge of the housing.

Is the ...373 a similar piece? Was it used in later L-88/ZL-1 applications? Do you have one in The Collection? Is it still available from GM?

Duke

[Joe L.]

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

Joe - back when I was involved with the new '67 "12-mile-L-88" it had a conventional VAC, but the nipple was cut off so a hose could not be attached. I don't recall the ID number.

My Cosworth Vega was built without a VAC (It has one now,), and had a plastic "plate" in place of the VAC to hold the radial position of the pickup coil. It didn't protrude beyond the edge of the housing.

Is the ...373 a similar piece? Was it used in later L-88/ZL-1 applications? Do you have one in The Collection? Is it still available from GM?

Duke

Duke-----


Yes, the '373' vacuum controls had the "cut off" nipple. Actually, it looked more like a "hollow rivet" had been installed since it looked like "turned over" metal. Seems like I might have seen some that have a completely "blank" face. In other words, no hole or nipple, at all.

The GM #1115373 was used for all 1967-69 L-88 and ZL-1.

I do not have one. It was discontinued without supercession in December, 1987. They usually sell for Big $$$ these days on eBay.

[Christopher R.]

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.