Determining top dead center
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*Max Advance | *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 | + | *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. |
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| + | *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. | ||
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