A Buick V6 has 11:1 compression, a high energy ignition and turns 5,000 rpm. With the specifications given, you will have to retard the timing for the high compression, low rpm and high energy ignition. By comparing the engine’s specifications against the chart, a usable timing guideline can be found. Engines with a combination of items from both columns will require a timing that is set in the mid range.

Obviously a full technical explanation of correct ignition timing would be very complicated. The best way to arrive at a suitable ignition curve for your engine is to use the Ignition Timing Factors Chart as a guide and compare it to the Advance Graphs in Figure 2 until a suitable curve is found. When selecting your advance curve, use detonation (engine ping) as an indicator of too much advance, and a decrease in power as an indicator of too little advance.

TIPS ON SELECTING AN ADVANCE CURVE
• Use as much initial advance as possible without encountering excessive starter load or engine kick-back.
• Start the centrifugal advance just above the idle rpm.
• The starting point of the centrifugal advance curve is controlled by the installed length and tension of the spring.
• How quickly the centrifugal advance (slope) comes in is controlled by the spring stiffness. The stiffer the spring, the slower the advance curve.
• The amount of advance is controlled by the advance bushing. The bigger the bushing, the smaller the amount of advance

The following procedures are for the PN 8551 Distributor. The centrifugal advance mechanism is made up of weights, springs, an advance cam and the advance stop bushing. The distributor can be used in a wide selection of applications by changing only the springs and the advance stop bushing. There is no need to change the weights or advance cam.

SELECTING THE ADVANCE SPRINGS
The rate, or how quick the advance comes in is determined by the type of springs which are installed on the distributor. The MSD distributors are equipped with two Heavy Silver springs installed. These will give you the slowest advance curve possible. The parts kit contains two additional sets of springs which can be used to match the advance curve to your particular application. Refer to the Spring Combination Chart (Figure 2) for combinations that can be achieved.

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