Other conditions being equal, the proper timing for an ethanol engine is five to eight degrees advanced from the optimum gasoline setting. But as you make changes described in this chapter, you will change factors that affect the proper timing. Improved manifold heating and increased compression ratio require retarding the timing. So does enriching the fuel-air ratio. With a moderate increase in compression ratio and manifold heating, ignition timing will be more like three to five degrees advanced from the ideal gasoline timing.

Gasoline engines without emission controls (through 1967) come with optimum spark timing.

On most 1968-70 cars, timing was retarded to reduce emissions of oxides of nitrogen (NO_x). Ethanol combustion produces much less NO_x than gasoline, so it is acceptable to advance the timing more on these cars to regain the efficiency and drivability lost to retarded timing.

Starting in 1971, automakers used a variety of devices and concepts - some of which include spark-timing controls - to reduce NO_x. How you adjust the timing on these cars will depend on the components of your emission control system and is beyond the scope of this book.

A gasoline engine will knock if the timing is too advanced, but not so with ethanol. Unless you have use of a dynamometer, the best way to check your timing setting is on the highway. Time your acceleration from about 30 to 55 MPH with a three-degree advance, and keep advancing the timing until you get the fastest acceleration time. The minimum spark advance for best power is your goal

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