Monday, November 20, 2006

VW - CDI and $$

CD Ignition and $$$

While there is an initial cost for everything, some things are well worth the expense, as in the case of adding a Capacitance Discharge ignition module to an early Volkswagen engine.

Stock ignition does a fine job at low speed but as engine RPM rises, spark voltage falls. This is in response to fundamental electrical laws. In the stock system, as the points age and the rubbing block wears, resistance rises while system ‘on-time’ falls, further reducing the available spark energy. At 3,000 RPM the available spark energy may be only a quarter of the idle speed value. The result is incomplete combustion and an overall drop in engine efficiency.

CD ignition is justified because it provides 100% of the possible spark energy at ALL engine speeds.

The most notable improvement is increased fuel economy. Some users claim up to 25% increase in miles-per-gallon. In my ‘67 bug I get 35-37 mpg on long trips (>400 miles) at highway speed. Before installing the CD, I got 28-30. On that basis alone the CD is well justified. But then there are the added advantages of reduced maintenance and prolonged spark plug life.

Having used electronic ignition systems on a variety of vehicles . . . including a home built airplane . . . for more than twenty years, finding such systems on modern cars and motorcycle is really no surprise; CDI is superior to what has gone before.

-Bob Hoover

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