Which spark plug is better, fine wire or massive electrode?
Let’s examine the facts. We’ll use a normally aspirated Cirrus SR22 as an example.
The Continental IO-550 engine has twelve spark plugs. 12 new massive electrode Champion spark plugs would cost $450 (average $30 each, plus $90 installation labor) and last 600 hours, with proper care. That’s 75 cents an hour initial cost. For only 600 hours of service life.
Massive electrode plugs require more cleaning and tend to foul from lead accumulation. Servicing 12 plugs takes 3-4 minutes each, adding 45 minutes to each 100 hour service. There will be five services at $68 each for a total of $340. Added to the $450 initial cost, we have $790 total, for a cost of $1.31 per hour.
Compare that to Champion’s fine wire plugs, at $1100 a set, $1190 total installed. We normally expect 1600-2000 hours from these plugs, but let’s use 1600 for comparison. You’ll spend 74 cents per hour, initial cost. Fine wire plugs don’t foul easily, and rarely collect lead deposits due to the open electrode design. The gap stays stable due to the iridium wire’s resistance to wear. That cuts servicing costs by forty percent, to about $40 per service, times 15 events, for $600 in service costs over the life of the plugs. Now our total costs are $1790, for a cost per hour of $1.12.
Not a big savings, yet, just 19 cents per hour…. But wait, we have to account for the shorter life of the massive electrode plugs. Even though the difference is 2.6 times shorter life, let’s be generous and say we can stretch the massive electrode’s service life to 800 hours, cutting the difference to 2-1. Now we have to buy another set of massive electrode plugs at $450, and service the two sets a total of 14 times (the original 5 times we calculated on a 600 hour life, plus two more services assuming a greater 800 hour life per set, and 7 more times for the second set of plugs) for a total of $952 in labor. So we’ve spent $450 on a second set of massive plugs, just to equal the service life of one set of fine wire spark plugs. Now the total cost of the massive plugs is $1852 over 1600 hours, compared to $1790 for the one set of fine wire plugs. And remember, we’ve stretched the life of the massive plugs to 800 hours, which is possible, but rarely attainable. Using the more realistic 600 hour life span of massives, you’ll use 2/3 the value of an of another set, or $297, to equal the service life of the fine wire plugs. So we are looking at savings of $62 to $359 on spark plugs and labor over an equal time span. Still not a big savings, yet.
So let’s consider fuel efficiency…
RAM Aircraft of Texas has studied the differences, and concluded that turbocharged Continentals are 2.2 percent more efficient with fine wire plugs installed. They also say that 1 percent is a reasonable expectation in other engines. So let’s use the lesser number, 1 percent, on our Cirrus SR22.
On a typical fuel burn of 17 gallons per hour over 1600 hours, at $5 per gallon, we will use $136,000 worth of fuel. Yes, I remember when avgas was $2 a gallon, not so long ago…
Saving just one percent on that gives us $1360 in savings, and if we could attain RAM’s 2.2 percent efficiency gain, we’re saving $3000 in fuel over the life of the plugs. More efficient combustion has other benefits such as lower oil consumption, reduced exhaust system wear, etc, but those are beyond the scope of this discussion.
This comparison has been among Champion’s two competing offerings. Their fine wires offer savings of $1422 to $1719 over 1600 hours. And it is safe to say that a good fine wire plug will last much more than 1600 hours. Many will go to 2000 hours with proper care.
Now, let’s compare the Tempest fine wire plugs as well.
Since the Tempest fine wire plugs are over 30 percent less expensive than Champion’s, you’ll keep at least another $400 in your pocket during this 1600 hour span. That’s $1800-2100 in savings over massive electrode plugs, based on one percent gain in fuel efficiency. Turbo models will save much more, based on RAM Aircraft’s studies.
Retail prices will vary of course, changing the total costs but the ratios will remain fairly constant. When you “plug” in your local costs, you’ll find the long-term savings of fine wire plugs tip the scales in their favor. You’ll find the differential is actually greater in practice, in favor of fine wire plugs.
Along with the cost savings comes increased reliability, and that’s what we’re really after here, isn’t it?