Correct vacuum advance for '65 396 cars

[Tony S.]

There has been some discussion in the past regarding the correct vacuum advance used on '65 L78 (396/425) cars. The discussion seemed to go away from the 201 (called out as correct in the '65 JG) and in favor of either the 355 or 360 can. I'm in the process of troubleshooting some vacuum issues with my car. Is it the feeling that the 355 is the correct one?

Would it matter what options came with the L78 car in '65? Power brakes takes vacuum. I just wonder if there might have been more than one vacuum advance used in 1965 production depending on the car's options?

Thanks.
Tony

[Wayne M.]

Re: Correct vacuum advance for '65 396 cars

There has been some discussion in the past regarding the correct vacuum advance used on '65 L78 (396/425) cars. The discussion seemed to go away from the 201 (called out as correct in the '65 JG) and in favor of either the 355 or 360 can. I'm in the process of troubleshooting some vacuum issues with my car. Is it the feeling that the 355 is the correct one?

Would it matter what options came with the L78 car in '65? Power brakes takes vacuum. I just wonder if there might have been more than one vacuum advance used in 1965 production depending on the car's options?

Thanks.
Tony

Tony -- here's a pic of the page in the Delco 1964-66 DR-324S supplement; distrib 1111093 is on the bottom line. Far right column is the distr's vac advance. I have two more of these supplements ('64-68; '64-76) and they all show same for the '093'.

PB was not a constant consumer of engine vacuum, so I don't think that would affect the distrib. installed. (still used an IF suffix 396 block). But in '66 and up, with A.I.R., etc. the map changed per some equipment, and the Delco/GM solution was to design / specify a different distributor.

[Duke W.]

Re: Correct vacuum advance for '65 396 cars

According to the L-78 specs published in Corvette News, the VAC matches the 201, but the Delco data presented by Wayne shows otherwise.

In any event, you need a VAC that provides full advance at 12" since your engine generates about 14"@900. This is not sufficient to pull the 201 to the limit which requires nominally 15.5", so it does not comply with the "Two-Inch Rule"

The VAC I recommend for all SHP big blocks is the Echlin VC-1765 or equivalent in any other brand, all of which should be stamped "B20", and its specs are 0@6", 16@12".

The 355 was used on base engines beginning in '66, and it is a good match for that engine with a manual trans. The aftermarket equivalent is Echlin VC-1802 or equivalent, stamped "B22" This is a 15" VAC and the 327/300s 18"@500 in neutral makes it a good match, but I recommend the B20 for 300 HP with Powerglide.

Corvette News lists L-72 max. vacuum advance as 12@12", and I believe this is the 360, which is okay to use. There is no aftermarket exact equivalent to the 12* advance, so if one doesn't have a properly functioning 360, I recommend the B20, which has 4 more degrees at the same 12".

At least L-78 has full time vacuum advance

What's the ID of the currently installed VAC?

[Tony S.]

Re: Correct vacuum advance for '65 396 cars

Wayne and Duke. Thanks for the info. When I restored my car, I followed the JG and installed a 201 can. At chapter judging, one of the judges told me that the JG was wrong and that I needed to install the 355, so that's what I bought. After judging (when I'm more concerned with "go" than "show"), I may go with one of the well built modern cans as you have suggested. In the meantime, I'm getting ready for Waco.

Thanks guys!
Tony

[Howard P.]

Re: Correct vacuum advance for '65 396 cars

This response is directed to Duke Williams

Duke

I have been following your advice regarding the VC1765 vacuum can and purchased one today from my local NAPA store. The box is marked VC1765 however the pot inside is marked B26 not B20 as per your notes. I cannot find any notations for the specs on the B26. Do you think it may be that the B20 are now being replaced by the B26 unit ?

My application is a 67 L89

Thanks

Howie

[Duke W.]

Re: Correct vacuum advance for '65 396 cars

Going from memory, a few years back there was another NAPA VAC part number that had the same specs as the VC-1765/B20. I don't remember the part number, but IIRC the ID was B26.

Apparently both B20 and B26 were consolidated under the one VC-1765 part number.

What you need to do before you install the B26 is check it with a Mighty Vac that it meets the recommended spec. Within plus/minus 2" Hg. the pull rod should start to move at 6" and stop at 12".

If it passes the above test, install it on the engine and check that it starts advancing at nominally 6" and provides within one degree of 16 deg. max. total advance at near 12".

Let us know what you find. Knowing that this is a slow moving part, I guess I'm not surprised that there are still some B26 VACs in VC-1765 boxes several years after the consolidation.

Make sure you convert the L-89 from ported to full time vacuum advance to go with the new "functionally correct" VAC.

Duke

[Howard P.]

Re: Correct vacuum advance for '65 396 cars

Duke

Thanks for your advice and information. I will try this nxt weekend when I can get at the car again. Will let you my findings

Howie

[Duke W.]

Re: Correct vacuum advance for '65 396 cars

I found the discontinued Echlin part number for "B26". It was VC-1808, and verified that the nominal published specs are the same as VC-1765/B20.

But I always recommend checking new VACs as I stated above - the "precheck" prior to installation and a final check on the car.

It's been so long since I heard of someone running across a B26, I had forgotten the details.

Duke

[Stuart F.]

Re: Correct vacuum advance for '65 396 cars

Duke;

The B26 seems to have become the "generic" VAC that NAPA (anyway) consolidated a number of units into, including the VC176 and VC181. I took a chance some time back and ordered what was listed as a B20 replacement through a store here which tapped the Atlanta warehouse and it came in stamped as a B26.

Stu Fox

[David C.]

Re: Correct vacuum advance for '65 396 cars

Whatever unit you get, be sure test it for accuracy per Duke's instructions. I have yet to find a correctly stamped can for judging that operates within specs and have opted for a correctly operating Elkin unit for go.

[Stuart F.]

Re: Correct vacuum advance for '65 396 cars

Right you are David. I ordered two #236 VAC's from two different sources, neither of which was anywhere near spec. They both looked nice, that's all. Without a Mityvac I'd be lost. Such a simple device can save you a whole lot of grief.

Stu Fox

[Duke W.]

Re: Correct vacuum advance for '65 396 cars

Duke;

The B26 seems to have become the "generic" VAC that NAPA (anyway) consolidated a number of units into, including the VC176 and VC181. I took a chance some time back and ordered what was listed as a B20 replacement through a store here which tapped the Atlanta warehouse and it came in stamped as a B26.

Stu Fox

I have no listing for Echlin VC-176 or VC-181 VACs applicable to Delco single point/TI distributors.

[Stuart F.]

Re: Correct vacuum advance for '65 396 cars

Duke;

Sorry, I stand corrected. I was looking at the wrong notes on the subject. It should be the NAPA VC1820 (B28) and their VC1765 (B20) have been consolidated under VC1675 (B26). It tested with the Mityvac at;

begins; @ 6.0 to 6.5" Hg.
All In; @ 12.5 to 13.0" Hg.

I never ran it on the distributor machine to quantify it's advance degrees, but it looks like a 15.5 to 16.0.

Sorry for the error. I've had one eye on the TV weather all day to decide whether to prep for "Hanna" or not. Right now I'm leaning toward not as I'd rather work on some Vette projects in the garage.

Stu Fox

[Duke W.]

Re: Correct vacuum advance for '65 396 cars

You're still not making any sense - VC-1675 is a 17" VAC, ID B13, and VC-1810 (B28) is apparently discontinued other than whatever stock may remain.

B26 (formerly VC-1808) and B20 have been consolidated under the same VC-1765 part number, and they both have the same nominal specs of 0@6" 16@12".

Duke

[Stuart F.]

Re: Correct vacuum advance for '65 396 cars

Duke;

You got my head spinning on this one. The VAC I ordered and received from NAPA is designated in my paper work (order and receipt) as a VC1675. The item I received is stamped as a B26.

I originally wanted to get a B28 from them, but they looked up that part which cross referenced to their #VC1820, and the computer noted that the VC1820 and the VC1765 (B20) in turn were consolidated under their VC1675. Not knowing what the performance specs would be on their VC1675, nor that it was stamped as a B26, I ordered it sight unseen on the chance it might have the specs of a B28 (I was desparate at the time). I know this sounds confusing and may conflict with your data (and my track record today is not so good), but I have confirmed this is the data I was shown from a NAPA computer.

Perhaps you or someone who has easy access to the NAPA data can check this out to be certain.

Stu Fox