1967-02-01

High Altitude Can Affect Automotive Ignition System Performance 670147

To evaluate spark plug and ignition system requirements at high altitudes, tests were made in mountainous areas and in the laboratory using an altitude simulator. In the latter phase, both a standard compression ratio and a typical “export” compression ratio were investigated. In addition both compression ratios were tested using standard carburetion and typical high altitude carburetion.Spark plugs at least one heat range hotter than normal can be used if a vehicle is continuously driven at altitudes above 5000 ft above sea level. However, since spark plug voltage requirements increase at road load conditions and flashover voltages decrease at higher altitudes, more frequent maintenance of spark plugs and ignition systems is desirable in high altitude areas.When an engine adjusted for optimum performance at higher altitudes is driven at wide open throttle at sea level, preignition and detonation may be encountered.

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