Spark Plugs – Fine Wire vs. Massive

For turbocharged piston twins flying at high altitude, fine wire spark plugs are more effective at igniting a fuel air mixture. They induce less strain on the magnetos and simply prove to last longer.

Operators have advanced their conviction that certainly a set of fine wire plugs are good for 1,000 hours. Other operators have suggested even longer periods. We note that since advising operators of our 350 hp liquid-cooled engines to switch to fine wire plugs, our service managers do not recall any customer contacts regarding ignition performance at altitude.

There are two primary reasons why fine wire plugs are more effective than massive plugs. First, the massive electrode’s shear size shields its own spark from some of the fuel / air mixture around it. The result is less than even ignition which is less efficient. Second, the iridium alloy used in the fine wire plug allows the use of a larger spark gap. The larger gap results in a hotter more powerful spark.

Further, the gap of any electrode is vulnerable to erosion and melt down. The massive plug is especially susceptible due to the medium melting point alloy used in manufacturing it. The alloy has a tendency to erode at a less than cost effective rate, when compared to the longer life of the fine wire electrode. (In both cases, comparison is made when the spark gaps are set for optimum performance.)

Durability is also achieved with proper inspection, cleaning and gapping, when done in accordance with the guidance published by Champion Spark Plugs and Tempest® Spark Plugs by Aero Accessories. For example, Aviation Consumer reports: “The nickel-alloy used in massive electrode plugs makes them suitable for about 400 to 500 hours of operation with careful maintenance...” and “Fine wire plugs tend to last two to three times longer than massives and 1500 hours in service is not uncommon.” (www.aviationconsumer.com). However, without periodic re-gapping (typically done at 100 hour inspections) spark plug life may be reduced to half those recommended numbers.

RAM flight test data shows fine wire spark plugs to be 2.2% more efficient than massive electrode spark plugs. The TSIO-520-NB engine at high cruise or climb power (232 hp at 2400 RPM; EGT at Peak +100°F rich @ 10,500 ft.) yielded a Brake Specific Fuel Consumption of .498 for Fine Wire and .509 for massive plugs (BSFC = lbs. of fuel/hp/hour) (Both spark plugs had the same gap settings of .018 inches). The 2.2 % fuel savings (.498 vs. .509) could vary with other engine models. Fuel savings of 1% on various other engines seems a reasonable expectation. After testing fine wire spark plugs, and after noting the added efficiency, RAM recommends fine wire spark plugs.