Distributor Vacuum Advance Part #

[Frank D.]

Can anyone tell me the correct original GM part number for the distributor advance vacuum for a 1965 327/300 hp? The car has automatic and air conditioning. Can't seem to find a page with the part listed in the '65 AIM.
Thanks in advance.

Frank

[Wayne M.]

Re: Distributor Vacuum Advance Part #

Can anyone tell me the correct original GM part number for the distributor advance vacuum for a 1965 327/300 hp? The car has automatic and air conditioning. Can't seem to find a page with the part listed in the '65 AIM.
Thanks in advance.

Frank

Frank -- this info wouldn't be found in the AIM, as the engine (including distributor) arrived at St.Louis as an assembly.

The '65 TIM&JG calls for 1116236 vac cans for all 327's. The base engine and your L75 version use the 1111076 distributor. Hard to believe that same can would be factory-installed on mild thru wild motors.

But, the Delco Remy says the 076 distrib. was built with the 1116238 vacuum advance (stamped MS_238_24). So I'm tempted to suggest the Tech manual is possibly in error, or at least the 236 is a typo for this distrib.

Wish some members would report what's on known ORIGINAL (not restored, thanks) base and 300hp distributors.

[Duke W.]

Re: Distributor Vacuum Advance Part #

The JG is definately wrong on this issue. Only SHP/FI small blocks used the 236 VAC.

The '65 300 HP VAC was a one year only oddball. I don't know the OE part number, but the specs are 0 @ 6", 24 @ 13".

For '66 and '67 the 300 HP VAC specs are 0 @ 6", 16 @ 12". I think this VAC's last three p/n digits are "360", and this is what I recommend to replace all 300 HP/Powerglide VACs. It is stamped "B20", and is available from in all the normal aftermarket brands. The NAPA number is VC-1765.

For 300 HP/manual trans I recommend the VC-1802 "B22" 16" VAC, but PG needs a 12" VAC due to lower idle speed/vacuum in Drive.

Duke

[Joe L.]

Re: Distributor Vacuum Advance Part #

Can anyone tell me the correct original GM part number for the distributor advance vacuum for a 1965 327/300 hp? The car has automatic and air conditioning. Can't seem to find a page with the part listed in the '65 AIM.
Thanks in advance.

Frank

Frank-----


The correct, original part number for the distributor vacuum control for your application was GM #1116238. That part was discontinued in July, 1966 and replaced by GM #1115357, aka Delco #D1376. It's possible that some very late 1965 with base or L-75 may have originally used the 1115357.

The GM #1115357 was discontinued without supercession in February, 1993.

You can obtain a functional replacement for this vacuum control under
NAPA Echlin #VC 1605, Standard Motor Parts #VC-169, or current Delco #D1354C. All are the same and will be stamped "B9".

Tip: although the 111638 was the original vacuum control and all the others I mentioned are functional replacements of the original specs, ANY of these controls, including the 1116238, will cause your engine to be "pre-disposed" to pre-ignition under many operating conditions.

[Joe L.]

Re: Distributor Vacuum Advance Part #

Frank -- this info wouldn't be found in the AIM, as the engine (including distributor) arrived at St.Louis as an assembly.

The '65 TIM&JG calls for 1116236 vac cans for all 327's. The base engine and your L75 version use the 1111076 distributor. Hard to believe that same can would be factory-installed on mild thru wild motors.

But, the Delco Remy says the 076 distrib. was built with the 1116238 vacuum advance (stamped MS_238_24). So I'm tempted to suggest the Tech manual is possibly in error, or at least the 236 is a typo for this distrib.

Wish some members would report what's on known ORIGINAL (not restored, thanks) base and 300hp distributors.

Wayne----


I agree with Duke. Only the L-76, L-79, and L-84 used the GM #1116236, aka Delco #D1316A, vacuum control for 1965. The base engine and L-75 used the GM #1116238. Very late MAY have used the 1115357. The latter would require confirmation from known-original, late cars.

[John H.]

Re: Distributor Vacuum Advance Part #

There's lots of conflicting information on this VAC, depending on what GM source you look at; for instance, the 1965 Corvette Shop Manual Supplement shows the same VAC specs (0* @ 4" Hg. and 16.5* @ 8.2" Hg.) for all '65 Corvette applications and distributor numbers. That may be why the JG shows the "236" VAC for all 327's.

[Joe L.]

Re: Distributor Vacuum Advance Part #

There's lots of conflicting information on this VAC, depending on what GM source you look at; for instance, the 1965 Corvette Shop Manual Supplement shows the same VAC specs (0* @ 4" Hg. and 16.5* @ 8.2" Hg.) for all '65 Corvette applications and distributor numbers. That may be why the JG shows the "236" VAC for all 327's.

John----


The Shop Manual specification may be all or part of the reason that the JG shows the '236' for all 1965 applications. However, I'd say the shop manual is incorrect on this one. It may be that with the "236" and "238" numbers being so close, "somewhere along the way" someone in GM may have made a "typographical error" that is the genesis of the problem. That's just a guess, though.

[Duke W.]

Re: Distributor Vacuum Advance Part #

The "B9" VAC nominal specs are:

0 @ 4", 21 @ 17"

This is not a good functional replacement, especially for Powerglide as it may not consistently pull enough vacuum idling in Drive to keep the VAC "locked" at full advance. Lack of this will cause idle stabililty problems.

Over the years GM made what I consider to be "mistakes" in some OE VAC selections, but they were usually corrected in subsequent model years.

Examples include the '63 L-76, '65 L-78, and the various 300 HP VACs, which were finally "corrected" with a 12" VAC for '66 and '67 that was compatible with Powerglide.

There were literally a dozen or so VACs used in the pre-emission era, and the count expanded rapidly in the emission era.

I recommend VACs based on the best functional replacement, and one of three currently available replacements (actually now two since the B28 is out of production at the current time) mets needs of all non-emission engines from '57 to '67, and I've summarized the applications/VACs in previous threads.

As far as judging is concerned, the JG may or may not specify the OE number that is usually visible on the VAC mounting bracket, and the JG may or may not be correct. Or a judge can make a "system knowledge" call. In any event, if you have to replace an OE VAC the judge can deduct for a service replacement because of the "B-number", but I don't think any judge will deduct more points because the "B-number" specs do not match the OE specs, so if you have to replace an OE VAC, use the best functional replacement.

Duke

[Frank D.]

Re: Distributor Vacuum Advance Part #

Thanks for all your help. The original question comes because of my recent NCRS Top Flight judging. I lost points because the car had a service replacement can and I wanted to replace it with the original factory correct part.

Once again it is great having a resource so all-encompasssing that someone has the right information we need even when the manuals are incorrect!

[Joe L.]

Re: Distributor Vacuum Advance Part #

The "B9" VAC nominal specs are:

0 @ 4", 21 @ 17"

This is not a good functional replacement, especially for Powerglide as it may not consistently pull enough vacuum idling in Drive to keep the VAC "locked" at full advance. Lack of this will cause idle stabililty problems.

Over the years GM made what I consider to be "mistakes" in some OE VAC selections, but they were usually corrected in subsequent model years.

Examples include the '63 L-76, '65 L-78, and the various 300 HP VACs, which were finally "corrected" with a 12" VAC for '66 and '67 that was compatible with Powerglide.

There were literally a dozen or so VACs used in the pre-emission era, and the count expanded rapidly in the emission era.

I recommend VACs based on the best functional replacement, and one of three currently available replacements (actually now two since the B28 is out of production at the current time) mets needs of all non-emission engines from '57 to '67, and I've summarized the applications/VACs in previous threads.

As far as judging is concerned, the JG may or may not specify the OE number that is usually visible on the VAC mounting bracket, and the JG may or may not be correct. Or a judge can make a "system knowledge" call. In any event, if you have to replace an OE VAC the judge can deduct for a service replacement because of the "B-number", but I don't think any judge will deduct more points because the "B-number" specs do not match the OE specs, so if you have to replace an OE VAC, use the best functional replacement.

Duke

Duke-----


I don't know if a "B9" vacuum control is a "good" replacement for the original GM #1116238 and strongly consider that it is not. In fact, I strongly suggested in my original post that either an original 1111238 or any of the functional replacements for it are wise to use for a base or L-75 application.

However, the "B9" or NAPA VC-1605, SMP VC-169, or Delco #D-1354C are the FUNCTIONAL replacement for the GM #1116238. As I see it, the issue of whether ANY of these, including the original piece, are the best thing to use is a completely separate issue from the issue of functional replacement. In any event, when I use the term "functional replacement" I am using that term in the connotation that a certain REPLACEMENT part has equivalent functional SPECIFICATIONS to a certain original GM PART NUMBER.

The VC-1765, aka "B20", that you previously mentioned is a FUNCTIONAL replacement for the GM #1115355, aka Delco #D1382. The VC-1802, aka "B22", is a FUNCTIONAL replacement for the GM #1973437, aka Delco #D1308A. Either of these may well be a better REPLACEMENT choice for a 1965 base or L-75 engine application, but they are not, by my definition, a FUNCTIONAL replacement for the vacuum control originally used, the GM #1116238 (even though they may provide an improved function). The use of either the "B20" or "B22" is a MODIFICATION of the original distributor configuration, albeit a functionally favorable one.

[Stuart F.]

Re: Distributor Vacuum Advance Part #

Just a word of caution; there are a number of repro VAC's out there now which are correctly stamped, but do NOT perform as advertised. I bought two VAC's stamped "236 M 16" from two different sources. Neither would meet the specification for a 236 (B28); 0 deg. @ 4"hg. & 16 deg. @ 8"hg.. When testing with a Mityvac pump, they each were at;
0 deg. @ 8-9"hg. & 16 deg. @ 15-16"hg.

Both looked great and would probably pass visual inspection during judging, but they will not perform well on any 327 SHP 63 thru 67. I returned them both with a suggestion that they discontinue selling these for these applications or they will have a lot of unhappy Vette owners on their hands.

I don't know of any other incorrect VAC p/no's, but I'd recommend testing any before you buy. Mityvac pumps are not that expensive and are handy to have around for that occasional vacuum diaphragm or fuel pump test.

Stu Fox

[Joe L.]

Re: Distributor Vacuum Advance Part #

Just a word of caution; there are a number of repro VAC's out there now which are correctly stamped, but do NOT perform as advertised. I bought two VAC's stamped "236 M 16" from two different sources. Neither would meet the specification for a 236 (B28); 0 deg. @ 4"hg. & 16 deg. @ 8"hg.. When testing with a Mityvac pump, they each were at;
0 deg. @ 8-9"hg. & 16 deg. @ 15-16"hg.

Both looked great and would probably pass visual inspection during judging, but they will not perform well on any 327 SHP 63 thru 67. I returned them both with a suggestion that they discontinue selling these for these applications or they will have a lot of unhappy Vette owners on their hands.

I don't know of any other incorrect VAC p/no's, but I'd recommend testing any before you buy. Mityvac pumps are not that expensive and are handy to have around for that occasional vacuum diaphragm or fuel pump test.

Stu Fox

Stu-----


This is a major problem with many "reproduction" parts. While they may be configuration and appearance-correct, they are not functionally correct or they are quality-inferior to original pieces. I'm not surprised, at all, that this problem exists with respect to reproduction vacuum controls; I'd only be surprised if it didn't.

The vacuum controls manufactured by Standard Motor Products, while not exactly appearance-correct, are usually functionally correct. At least, every one that I have tested, to the extent that I could test it, was within original specs for the particular control. Is EVERY part that SMP manufactures functionally correct? I don't know; I have not tested every one they ever made. However, was EVERY original GM vacuum control functionally correct as to specs for its particular part number? I doubt it. Keep in mind, too, that the original specs provided for a range, not a "dead-on" number.

[Duke W.]

Re: Distributor Vacuum Advance Part #

Duke-----


I don't know if a "B9" vacuum control is a "good" replacement for the original GM #1116238 and strongly consider that it is not. In fact, I strongly suggested in my original post that either an original 1111238 or any of the functional replacements for it are wise to use for a base or L-75 application.

However, the "B9" or NAPA VC-1605, SMP VC-169, or Delco #D-1354C are the FUNCTIONAL replacement for the GM #1116238. As I see it, the issue of whether ANY of these, including the original piece, are the best thing to use is a completely separate issue from the issue of functional replacement. In any event, when I use the term "functional replacement" I am using that term in the connotation that a certain REPLACEMENT part has equivalent functional SPECIFICATIONS to a certain original GM PART NUMBER.

The VC-1765, aka "B20", that you previously mentioned is a FUNCTIONAL replacement for the GM #1115355, aka Delco #D1382. The VC-1802, aka "B22", is a FUNCTIONAL replacement for the GM #1973437, aka Delco #D1308A. Either of these may well be a better REPLACEMENT choice for a 1965 base or L-75 engine application, but they are not, by my definition, a FUNCTIONAL replacement for the vacuum control originally used, the GM #1116238 (even though they may provide an improved function). The use of either the "B20" or "B22" is a MODIFICATION of the original distributor configuration, albeit a functionally favorable one.

My definition of "best functional replacement" is a part that has performance specifications that are best suited to the application regardless of the part number or performance specifications of the OE part.

I would refer to your definition of "functional" as the "best OE spec" replacement, but the B9 does not qualtiy IMO based on the fact that it requires about 17" for maximum advance vs. 13" OE for the specs I quoted (from Corvette News Vol. 8 No. 3).

Being as how at least four VACs of different specifications were used on the 327/300 from '62 to '67, it's clear than GM was also looking for the best solution, and it took them awhile.

Often the final part number used in production is the best solution for earlier engines of essentially the same configuration, which is the case of the 327/300 from '62-'67.

In this case it was the 355, 0@6", 16@12", which is a good match for Powerglide, but more aggressive than necessary for a manual transmission, which is why I recommend a 15" VAC for 250/300 HP with manual transmissions.

VAC specifications are merely a "tuning" parameter - much like carburetor metering rods and jets, initial timing, centrifugal advance curve, etc. The ideal specification depends somewhat on driving environment and conditions and fuel composition, and as with any "tuning parameter" some system knowledge and ultimately some SOTP input based on experience is required. This is how I developed my "Two-Inch Rule".

Unfortunately, unlike metering rods and jets, or distributor weights/springs, any change to the VAC can be a judging issue, so it comes down to a matter of whether you want the "correct" OE part, or the best replacement part based on function as I defined above.

In this case the owner will have a tough time finding a "correct" OE 238 VAC being as how they have been out of production for decades. He might be able to find a used (and hopefully functional) example, but it could loose condition points.

This is the case with many engine configurations due to GMPD parts consolidations - like the "201" VAC that was used on several configurations, both SB and BB. It was apparently never available through service parts or only for a short time, and the GMPD replacement is not even a good match to the 201 based on specifications, and the 201 specifications are not a good match for some engine configurations that it was originally used on like '63 L-76.

The other alternative is to take the "OE replacement" points deduction and install the best functional replacement based on my definition above. One is likely better off with the better engine behavior that can be had with a best functional replacement, especially when even 40 year old used VACs are scarce. There are probably easier ways to reduce deductions.

It would help if someone with the '65 AMA specs could state what they list as VAC specs for the '65 250 and 300 HP engines.

Duke

[Joe L.]

Re: Distributor Vacuum Advance Part #

My definition of "best functional replacement" is a part that has performance specifications that are best suited to the application regardless of the part number or performance specifications of the OE part.

I would refer to your definition of "functional" as the "best OE spec" replacement, but the B9 does not qualtiy IMO based on the fact that it requires about 17" for maximum advance vs. 13" OE for the specs I quoted (from Corvette News Vol. 8 No. 3).

Being as how at least four VACs of different specifications were used on the 327/300 from '62 to '67, it's clear than GM was also looking for the best solution, and it took them awhile.

Often the final part number used in production is the best solution for earlier engines of essentially the same configuration, which is the case of the 327/300 from '62-'67.

In this case is was the 355, 0@6", 16@12", which is a good match for Powerglide, but more aggressive than necessary for a manual transmission, which is why I recommend a 15" VAC for manual transmissions.

VAC specifications are merely a "tuning" parameter - much like carburetor metering rods and jets, initial timing, centrifugal advance curve, etc. The ideal specification depends somewhat on driving environment and conditions and fuel composition, and as with any "tuning parameter" some system knowledge and ultimately some SOTP input based on experience.

Unfortunately, unlike metering rods and jets, or distribtor weights/springs any change to the VAC can be a judging issue, so it comes down to a matter of whether you want the "correct" OE part, or the best part based on function as I defined above.

In this case the owner will have a tough time finding a "correct" OE 238 VAC being as how they have been out of production for decades. He might be able to find a used (and hopefully functional) example, but it could loose condition points.

The other alternative is to take the "OE replacement" points deduction and install the best functional replacement based on my definition above.

It would help if someone with the '65 AMA specs could state what they list as VAC specs for the '65 250 and 300 HP engines.

Duke

Duke-----


For 1969-1970 300 hp engines they must have forgot what they learned earlier about the vacuum controls because for these engines they used the GM #1115357 vacuum control (which replaced the 1116238 and has virtually identical specs).

[Stuart F.]

Re: Distributor Vacuum Advance Part #

Joe;

I understand the range issue, in fact when I tested the VAC's with my Mityvac I got slightly different readings each time. I was looking for one unit that would fall consistently within Duke's two (2") inch rule. I was looking strickly for functional performance as I was applying it on my 63 340hp for improvement of drive ability and, of course, no 63 SHP came with a 236 M 16 in the first place.

Stu Fox