Max Advance
Since the vacuum advance control unit is a part of the distributor, the number of degrees of vacuum advance is
specified in DISTRIBUTOR degrees - NOT crankshaft degrees. When talking about these control units, it is
important that you know whether the person you're talking to is referring to the distributor degrees, or if he's talking
crankshaft degrees. All of the listings shown in the following chart, and in any shop manual & technical spec sheet,
will refer to distributor degrees of vacuum advance. You must DOUBLE this number to obtain crankshaft degrees
(which is what you "see" with your timing light). Thus, a vacuum advance control unit with 8 degrees of maximum
advance produces 16 degrees of ignition advance in relationship to the crankshaft. When selecting a unit for max
advance spec, the total centrifugal timing at cruise must be considered. Thus, a car set up to produce 36 degrees of
total mechanical advance at 2500 rpm needs a vacuum advance control unit producing 16 degrees of crankshaft
advance. This would be an 8-degree vacuum advance control unit.
Max Advance @ "Hg
This is the range of manifold vacuum at which the maximum vacuum advance is pegged out. In selecting this
specification, you must consider the vacuum produced at cruise speed and light throttle application. If your engine
never produces 20" Hg, you better not select a control unit requiring 21" Hg to work.
The following listing (Non-HEI) is as follows: The first two part number listings are the two numbers that are most
commonly used in a Chevrolet performance application. The "B1" can is the most versatile and user-friendly unit
for a good performance street engine. As you can see, it was selected by GM for use in most high performance
engines due to its ideal specs. The "B28" can was used on fuel injected engines and a few select engines that
produced very poor vacuum at idle. The advance comes in very quick on this unit - too quick for many performance
engines. Do not use this very quick unit unless you have a cam/engine combination that really needs an advance like
this. It can be used as a tuning aid for problem engines that do not respond well to other timing combinations, and
can be successfully used in applications where direct manifold vacuum is applied to the can (see paragraph and
discussion on this above)
After this, the listing is by Echlin part number. The Chevrolet applications are listed first by application, followed
by a complete listing of all of the units used on any GM product (all GM units are interchangeable, so you can use a
Cadillac or GMC Truck unit on your Vette, if that's what you want to do).
Non-HEI Distributors:
P/N ID# Application Starts @ “Hg Max Adv
(Distr. Degrees @ “Hg.)
VC680 B1 1959 – 63 All Chevrolet 8-11 8 @ 16-18
1964 Corvette exc. FI
1964 Impala, Chevy II
1965 396 High Perf.
1965-67 283, 409
1966-68 327 exc. Powerglide
1967-68 All 396
1969 Corvette 427 High Perf.
1969 396 Exc. High Perf.
1969 Corvette 350 TI
1969-70 302 Camaro
1970 400 4-bbl
1970 396 High Perf.
1970 Corvette 350 High Perf.
1973-74 454 Exc. HEI
VC1810 B28 1965 409 High Perf. 3-5 8 @ 5.75-8
1965 327 High Perf.
1966 327 High Perf.
1964-67 Corvette High Perf. FI
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