The 1966 Mustang was built with a 200-cubic inch straight-six engine and a 289 eight-cylinder engine. Both engines must be calibrated or tuned-up periodically to ensure that they operate at their most efficient. This periodic calibration is required because parts wear out and can fall out of adjustment. When either occurs, power will decline and fuel efficiency will suffer. Fortunately, both engines feature a simple design and generally take less than one hour to tune up.
The 200 engine was equipped with type BF-82 spark plugs. The 289 engine featured type BF-42 plugs. The spark plug gap for both engines was .034 inches.
If the 200 engine was mounted to a manual transmission, the timing specification was six degrees before top dead center. If mounted to an automatic transmission, the 200's timing specification was 12 degrees before top dead center. Whether equipped with a standard or automatic transmission, the timing specification for the 289 was six degrees before top dead center.
Once the engine is hot, the 200's factory idle speed specification was 575 revolutions per minute (RPM) with a manual transmission and 500 RPM with the automatic transmission. The 289's factory idle speed specification was 575 RPM with a manual transmission and 475 RPM with the automatic transmission.
Dwell angle for the 200 engine must be within a range of 37 and 42 degrees. Factory specifications for the 289 call for a dwell angle of between 26 and 31 degrees. Ignition point gap for the 200 was .025 inches and .017 inches for the 289.
