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455CI Pontiac Engine Build - What's Your Problem?

I consulted some magazine articles and books, and most seem to agree that I need about 34-36 degrees total timing. I had a friend with a timing light check the car, and it seems to have only 6 degrees. Adding another 30 seems like a lot. In fact, when we tried to put it past 15, it started to run worse. I talked to a mechanic, and he said I needed to have the distributor recurved by a speed shop so that the weights and springs can be adjusted. I'm not sure what he means-I don't see any weights or springs in my distributor, though I have seen them in pictures in magazines. There are no speed shops around here, and I don't want to take the car apart and ship out my distributor. Also, what's the deal with vacuum advance? Some people say disconnect it; some say I have to keep it. I wanted to add an aftermarket ignition booster box, like an MSD, but I was told it can't be done with breaker points. Do I need electronic ignition? Should I forget the MSD?

Joe Pea, MSD Technical Advisor: Sounds like a good plan on the Cougar, Steve. Let's start with the ignition timing. There are a couple of different timing settings that need to be considered. Remember, one timing setting is not ideal for the variety of rpm an engine runs through. As rpm increases, the engine requires different ignition timing due to a number of changes, such as the dynamics of the air/fuel mixture entering the cylinder or the reduction in time that the mixture has to burn and combust due to increased piston speed through the combustion stroke.

To compensate for these changes, most distributors are equipped with a centrifugal (or mechanical) advance assembly to alter the timing and meet the demands of the engine. This advance system is made up of weights and springs. As the distributor spins faster, the weights overcome the strength of the springs and push out due to centrifugal force. This in turn advances the timing by moving the pickup assembly.

So when you set your timing, remember that adjusting it at idle is only part of the job. You also need to know the centrifugal amount that the distributor provides. This amount varies depending on the weights, the strength of the springs, and whether or not there is a stop bushing. The centrifugal advance that you set with your distributor will be added to this initial timing to produce your total timing. For example, if you have 10 degrees of initial timing and 21 degrees of centrifugal advance built into the distributor, the total timing will be 31 degrees.

On MSD distributors, the advance assembly is built on top to make adjustments easy (a stock Ford has the advance built under the trigger plate). To control how quickly the timing advances, MSD supplies each distributor with three pairs of advance springs. These springs hold the weights in until a point when the centrifugal force overcomes the spring tension, which controls the slope of the advance curve. Heavy springs with higher tension slow the rate of advance, while the lightweight springs allow the timing to advance rapidly with rpm.

The amount of centrifugal advance that occurs is controlled by a changeable stop bushing. These bushings feature different diameters that limit the movement of the advance plate. MSD includes four different advance stop bushings that will limit the centrifugal timing to 18 degrees, 21 degrees, 25 degrees, and 28 crankshaft degrees.

To check the total timing, you need to run the rpm of the engine up and watch the timing mark on the balancer. When it stops advancing, you'll see the total timing. Unless you have a dial-back timing light or a fully degreed balancer, you probably won't see the timing. MSD also offers a handy timing tape that easily applies to the balancer so you can set the total timing accurately. These tapes are sized for specific balancer diameters. Another thing to remember when you're checking the timing is to disconnect and plug the vacuum advance.

As far as running an external ignition control, such as an MSD 6A, you can easily connect one to a breaker-point distributor. As long as the distributor's advance and trigger are in good operating condition, running with points will work great. In fact, the points will last much, much longer because there is only a small amount of current going across the gap to trigger the MSD. Your engine will receive the benefits of MSD's powerful multiple sparks for improved throttle response, idle quality, and driveability.

More Info

MSD Ignition; El Paso, TX; 915/855-7123; msdignition.com

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