396 Vacuum Advance

[Daniel W.]

Hello,
Does anyone have the specs for the 201 vacuum advance supplied with the 093 distributor? At what vacuum does it start advancing the timing, when is it fully in, and what is the total advance?

Thanks,
Dan Wilson

[Michael H.]

Re: 396 Vacuum Advance

Dan,

I believe the "201" vacuum advance unit that you have is a 63-64 unit for a 327, not the correct unit for 396 or 427 with an 093 distributor. The 201 would be totally incorrect (and slightly dangerous) for a big block. The 201 was 15.5 deg and the correct unit for 396-427 was about 12 deg. Is your car a 327 or a big block?

Michael

[Everett Ogilvie]

Re: 396 Vacuum Advance

Dan, when we spoke earlier today my memory was on the fritz and I should have called out the 360 as the vacuum can for the 093 (I have 3 unrestored original 093's and all have the 360). It is marked MS 360 12 - I will email you a pic. Long Island incorrectly places the 425HP engines (L78 and L72) in the same category as all the '63 engines and some others. I recall discovering their inaccurate listings some time ago, and I confirmed the 360 as original equipment in 093 distributors in the earliest parts manuals, dated '65-'66 (later parts books do not list the original cans, they list generic replacements so you must use the '65-'66 book).

[Daniel W.]

Re: 396 Vacuum Advance

Michael,

The car is a big block car that we are trying to return to orginal condition for judging. It had a generic B1 on it when it was purchased. I have tested (with a hand vacuum pump/gage) both the B1 and the 201 and they are quite a bit different.

The current judging guide indicates a 201 is correct for the 396 engine.

Thank you all.

[Everett Ogilvie]

Corvette News for 1965

lists the L78 vacuum advance as starting at 8" Hg, with a total of 15 degrees @ 15.5" Hg.

Corvette News for 1966 (same distributor) lists the L72 vacuum advance starting at 6" Hg, with a total of 15 degrees @ 12" Hg. This issue states that all ratings are in engine degrees.

I believe the TIM is in error regarding the 201, as is Long Island. Dave Fiedler has also confirmed that the 360 can is correct for the 093.

[Michael H.]

Re: Corvette News for 1965

Everett,

You are correct. There was some confusion as to which unit was correct for 65 with 396 engine. My July 1966 parts book incorrectly lists two different part numbers for this application. The first is "65 Pass, Corvette (W/Sp. H/Per W/T. Ign).....1116163. The second, on the very same page, lists "65-66 Corvette w/Sp H/Per. (396-427).....1115360.

This has been a very confusing issue for years but I believe the 1116163 is totally incorrect as it is a 16 degree unit, way more than either of these 425 HP engines needed. The 1115360 is a 12 degree unit and is the only one listed for both engines in later parts books.

I suppose it is possible that some early 65 396 cars may have had the 163 unit but my 14971 car had what looked to be the original 360 unit before restoration and that was probably one of the first ten or fifteen cars built.

Michael

[Joe L.]

Re: 396 Vacuum Advance

Everett and Dan-----

As far as I can tell, the '093' distributors originally used several different vacuum controls. The earliest listing that I can find as far as GMSPO is concerned (10/65) shows vacuum control GM #1116163 (Delco D-1328) as applicable to the '093' distributor. However, control GM #1116201 was a predecessor part number to the 1116163. The 1116201 was discontinued from SERVICE in January, 1965 and replaced by the GM #1116163. However, from what I can tell, the GM #1116201 might have continued to be used in PRODUCTION-only, right through about the early 70s. If so, then the GM #1116163 was its SERVICE-only equivalent.

By July, 1966, GMSPO was showing BOTH the GM #1116163 AND the GM #1115360 (Delco D-1383) vacuum control as being applicable to the '093' distributor. That seemingly erroneous "dual application" was continued right through December, 2000 when the GM #1115360 was finally discontinued from SERVICE without supercession. Currently, the GM #1116163 is the only vacuum control catalogued as being applicable to the 1965 L-78 application and I believe it's still available.

Other sources, including Delco, indicate that the GM #1116236 (Delco D-1316A) or the GM #1115355 (Delco D-1382) might have been originally used on the '093' distributor.

[Everett Ogilvie]

Michael and Joe,

Thanks for the responses. Joe, as ususal your information is excellent, and seems to verify the confusion even within GM. Michael, I agree with you as far as what was actually being used late '65 clear through the '66 model year. My two early 450 cars (Oct 12, 65) AND my late May '66 Bowtie car all had the 360.

[William C.]

Re: 396 Vacuum Advance

My earliest reference calls for the 355 unit, 15 degrees (crank) total, starting at 6 inches, all in at 12 inches of vac

[Duke W.]

Re: 396 Vacuum Advance

As I believe was previously stated, the tuneup specs published in Corvette News show different vacuum advance specs for L-78 and L-72. The L-78 specs match the 201 or 163 can, but as is the case with the '63 SHP/FI engines, this can is not a good match to L-78 because it may not pull enough idle vacuum to lock the can at full advance at idle - assuming it has full time and not ported vacuum advance.

If anyone has the '65 and/or '66 AMA specs, please post the the vacuum advance specs for L-78 and L-72 as a cross check and note if there is a revision indication on the page. Since the AMA specs were updated as the year progressed, they should indicate any spec changes.

Asuuming the "360" can was used for L-72 and its specs are as published in CN, it would be a suitable replacement for L-78 (assuming you could find one). If not, the NAPA/Echlin VC1765 with 16 deg.@ 12" should be a good choice. These engines pull about 14-15" at 900 with full manifold vacuum to the can, which is enough to keep it locked to full advance at idle.

The VC1810 achieves the same result, but since it locks in the full 16 degrees at 8" it may increase the tendency to detonate under mild acceleration since it has a more aggressive curve.

Many of you may remember that many seventies vintage cars would detonate on light acceleration, but if you depressed the throttle further, the detonation would stop. This was because many cars of this era were set up with less than ideal initial timing, slow centrifugal curves, but lots of vacuum advance - up to about 24 degrees. These are lousy ignition maps, but they were set up this way as a compromise to achieve emissions targets first and get as good as possible fuel economy second. The result was a poor compromise that yielded poor driveability and detonation, but it was the best that could be done given the available technology at the time.

Duke

[Clem Z.]

you can limit the total vac advance

by installing a "stop" on the can mounting bracket using the orignal mounting screw. "been there done that"

[Bill W.]

Re: Corvette News for 1965

the engine from 16120 was removed at about 1 year old and has a 355...Bill