2 spark plugs per cylinder?
 

I know it's probably a stupid question but I was thinking about replacing the spark plugs on my 98 E-320. It requires 2 plugs per cylinder.
So what is the real advantage of having 2 of them? A resonance of spark?
Would both plugs be firing at the same time or just one? So that means they should last a very long time?

Not sure about the advantage but it's going to cost me quite a bit more:
12x8 = 96 vs
6x8 = 48 bucks.

Thanks in advance,
JeffreyP

The two plugs actually fire independently and may not fire at the same time depending on engine operating conditions.

The 3V arrangement precludes a centrally located plug, which is best for shortest flame travel and combustion time, which is best for both detonation control and thermal efficiency, so twin plugs get around this by creating two flame fronts.

It's not really a new idea; 3V twin plug engines have come and gone over the decades.

Reciprocating aircraft engines also have twin plugs fired by two completely independent magnetos, but in the case of aircraft engines it's a safety issue. If one ignition system fails, the second will allow the engine to continue operating, though at reduced power since the ignition systems are timed for best power when both are firing. If one quits the timing with just one plug would have to be advanced for peak power.

During engine runup prior to takeoff a pilot should always check both magnetos. The switch has postions for 1, 2, and "both". When switching from "both" to 1 or 2 there should be a specified RPM drop. If not, that mag is dead and you don't take off.

Duke

Change all of them. They all are subjected to the same environment. Two plugs are required for better combustion starting from two fronts. Airplanes have two plugs per cyl and you definately notice a power loss when you turn one set off.

Also be very happy you are not changing plugs on Howard Hugh's Spruce Goose. 8 engines, 28 cylinders each, 2 plugs per cyl and about $30.00 per plug.

$13,440

:D

John Roncallo

Thanks for the write up. So there are definite advantage. My complaint wasn't so much the cost but the labor involved as it's quite difficult to remove the plug boots. Now it's double.

Thanks,
JeffreyP

At least MB uses cheaper plugs. Plugs for an XJ8 cost $27 each x 16! :eek: