Does using dual spark plugs per cylinder make any difference?

Join the discussion
Registration is free. Ask a follow-up in this thread, or start your own.
Sign up Log in
39 replies · 18K views
berkeman said:
So each of the magnetos feeds one set of spark plugs for redundancy? Interesting...
During WW2, the test before takeoff was to run the engine up to temperature and speed, then cut one magneto at the time to check the fall in RPM. A "magdrop" of more than say 150 RPM, cancelled the flight.

I have a double toggle switch panel somewhere here, labelled "Magnetos".
 
Reply
  • Informative
  • Like
Likes   Reactions: Flyboy and berkeman
Physics news on Phys.org
Flyboy said:
I haven't touched a radial since school three years ago...

Lol, I haven't touched a radial since A&P school. . . 50 years ago. ( 1973 )

.
 
When I was about 14, I wandered into the local Euro-Sports-Auto sales lot. They had a red Ferrari with the hood up. I spent quite a few minutes looking at the engine. Counted the 12 spark plug wires. Eventually I asked the sales guy "why are there two spark plugs per cylinder?" -- annoyed, he told me "that's a twelve cylinder engine, kid."

Much later I had a hot-rodded HD sportster with dual plugs. As mentioned above, this does allow for less spark advance, a lot less.
 
Reply
  • Haha
Likes   Reactions: berkeman
I recall seeing Honda Odyssey many years ago with two plugs. (Not the car) It was only a single cylinder engine. Two stroke I would assume.
s-l400.jpg
 
Baluncore said:
During WW2, the test before takeoff was to run the engine up to temperature and speed, then cut one magneto at the time to check the fall in RPM. A "magdrop" of more than say 150 RPM, cancelled the flight.

I have a double toggle switch panel somewhere here, labelled "Magnetos".
Exactly right. Still done today on light piston planes, although it's more of a maintenance check every so often.
 
gmax137 said:
Sometimes, the second "plug hole" is for a compression release. Seen on old Brit bikes, if they don't have a "valve lifter."
That could be but I do recall a plug in each hole and a wire on each. The Odyssey I used to ride only had one and I don't recall a comp release.