Distributor Timing Essentials
by Don Caithness
photos by Don Caithness
Of the above factors, the rate of the advance curve will have the most significance on increased power. The distributor weights and springs control how quickly the advance comes in based on the RPM of the engine. If the combustion takes place while the piston is still moving towards TDC then detonation will occur, which over a short period of time will destroy your engine. If combustion happens after TDC then you lose power. The timing is critical. The factors that need to be considered are the rate of mechanical advance, combined with the total number of degrees of advance.
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| 5-The rotating inner time core passes by the fixed pole sending the signal to open the primary coil circuit. | 6-The unit from Performance Distributors is completely new right down to the casting. It’s a self-contained unit with no external boxes or coils but works like an HEI on steroids. |
The factory settings for mechanical advance, particularly in the later HEI units, are completely inadequate for hi-performance applications. Their advance curves may be lacking both in the total amount of advance and the advance curve due to the spring/weight/cam combinations. Some of the factors to be considered when calibrating the total advance and curve are the compression ratio, octane rating of the fuel, camshaft profile, cylinder heads and even the vehicle weight.
Now that you understand the theory, you can proceed in two different ways to set up your distributor. The first approach is trial and error and will consist of replacing the distributor advance weights and springs with those you will find in most speed shop kits. You’d be adjusting the initial timing, checking the rate of advance with a timing light and running the vehicle at the track to see the results. Since you are setting the distributor for the best die open throttle (WOT) performance, it wouldn’t be optimized for the street! Remember you also need to include the vacuum advance into the calculations. When the vacuum advance pulls in your total degrees of advance may be excessive and “pinging” will occur under light load. When this happens you’ll need to decrease your initial timing or increase the octane level of the fuel.
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| 7-The rotor is retained with nylon screws to prevent arcing or cross firing at higher RPM. | 8-The mechanical advance has been blueprinted (note the drill marks to remove the excess weight and control the centrifugal advance) for maximum performance and our specific application. The weight, spring and cam end are painted red for reference should you ever have to disassemble it. The Dyna-Module has more electronic dwell than a stock item. |
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