31 LaSalle Posted June 10, 2022 Share Posted June 10, 2022 while visiting a classic car show many years ago I saw an American fire engine with two v8 engines both with sixteen plugs one engine in the back to drive the water pump from memory I think it was pierce arrow but I could be wrong what would the purpose of two plug per cylinder be. Link to comment Share on other sites More sharing options...
ALF1920 Posted June 10, 2022 Share Posted June 10, 2022 (edited) I had a 1920 American LaFrance pumper with 3 spark plugs per cylinder. 2 each off of the distributor (for key start) and 1 each of of the magneto (for crank start). I believe it was to be able to ignite all the vapor at once. The cylinders were very large and cubic inch was well over 800. Edited June 10, 2022 by ALF1920 (see edit history) 2 Link to comment Share on other sites More sharing options...
Mike "Hubbie" Stearns Posted June 10, 2022 Share Posted June 10, 2022 It was in case one of the systems went down. From my understanding is they would start off with the battery and then switch to mag. If the truck started to have problems, they would go back to battery. Mike 1 Link to comment Share on other sites More sharing options...
JACK M Posted June 10, 2022 Share Posted June 10, 2022 Dependability, Multiple independent ignition systems. I would not want the pumper truck to break down if they were trying to put out my fire. 1 Link to comment Share on other sites More sharing options...
TerryB Posted June 10, 2022 Share Posted June 10, 2022 My 1989 Suzuki DR650 single cylinder motorcycle was equipped with dual spark plugs to make it more environmentally friendly and increase output power. In some instances dual plugs are redundancy for safety. Link to comment Share on other sites More sharing options...
joe_padavano Posted June 10, 2022 Share Posted June 10, 2022 Modern engines have used dual plugs for more complete combustion, either for emissions or increased power. Chrysler Hemi motors are a classic example. As noted above, other applications (aircraft, for example) use dual plugs and whole ignition systems for redundancy. 1 Link to comment Share on other sites More sharing options...
TAKerry Posted June 10, 2022 Share Posted June 10, 2022 I had a 1923 Norton Motorcycle with dual spark plugs. 2 Link to comment Share on other sites More sharing options...
TerryB Posted June 10, 2022 Share Posted June 10, 2022 (edited) My 2002 Suzuki 1000cc used factory installed dual electrode plugs rather than dual spark plugs for best combustion efficiency. They recommend changing them every 10k miles of use (at $15 each). Edited June 10, 2022 by TerryB (see edit history) Link to comment Share on other sites More sharing options...
Rusty_OToole Posted June 10, 2022 Share Posted June 10, 2022 Airplanes and fire engines used dual ignition for reliability. Two completely separate ignition systems meant the engine would continue to run even if one was disabled. Not just the spark plugs but the whole ignition system was duplicated. Some early luxury cars had dual ignition, battery for starting and magneto for high speed. That was because the early type of battery ignition made a good spark at low speed but got weaker as it sped up. While the magneto made a weak spark at low speed and got stronger as it sped up. Ford Model T had the trembler spark ignition, it was only good up to 2000 rpm or so but that is as fast as a Ford would go anyway. 4 Link to comment Share on other sites More sharing options...
31nash880 Posted June 10, 2022 Share Posted June 10, 2022 Have a 1931 Nash with straight 8 and twin ignition. 1 Link to comment Share on other sites More sharing options...
Marty Roth Posted June 10, 2022 Share Posted June 10, 2022 (edited) 3 hours ago, Rusty_OToole said: Airplanes and fire engines used dual ignition for reliability. Two completely separate ignition systems meant the engine would continue to run even if one was disabled. Not just the spark plugs but the whole ignition system was duplicated. Absolutely right ! Dad was a career firefighter, and the reason for Dual Ignition? the keyword is REDUNDANCY ! Edited June 11, 2022 by Marty Roth (see edit history) Link to comment Share on other sites More sharing options...
Pfeil Posted June 11, 2022 Share Posted June 11, 2022 16 hours ago, 31 LaSalle said: while visiting a classic car show many years ago I saw an American fire engine with two v8 engines both with sixteen plugs one engine in the back to drive the water pump from memory I think it was pierce arrow but I could be wrong what would the purpose of two plug per cylinder be. There are three answers, one is from a fire truck/airplane perspective, they can't afford a ignition failure, Two, race cars used them because the engine will make more power through more complete combustion. Three some late model cars from the 80's to today use them because of the more complete combustion and cleaner emissions, especially in the area of NOX emissions. 1 Link to comment Share on other sites More sharing options...
nickelroadster Posted June 11, 2022 Share Posted June 11, 2022 Marmons used dual plugs per cylinder in 1926-1928. They said it led to more complete ignition. You did have to make sure the plugs were syncronized in the distributor. 1 Link to comment Share on other sites More sharing options...
Marty Roth Posted June 11, 2022 Share Posted June 11, 2022 Slightly off-topic, but setting Dual Points can also be a fun way to spend part of your Saturday morning, waiting for the coffee to brew ... 4 1 Link to comment Share on other sites More sharing options...
Jim Mead Posted June 11, 2022 Share Posted June 11, 2022 I have a vivid memory of riding a single engine airplane. Switching on the second magneto brought 200 more rpm instantly, same throttle setting. There’s something to the time the flame front takes to progress from the spark. 1 Link to comment Share on other sites More sharing options...
joe_padavano Posted June 11, 2022 Share Posted June 11, 2022 11 hours ago, Marty Roth said: Slightly off-topic, but setting Dual Points can also be a fun way to spend part of your Saturday morning, waiting for the coffee to brew ... If you can do that BEFORE drinking coffee, my hat's off to you. 😁 1 2 Link to comment Share on other sites More sharing options...
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