Why 2 plugs per cylinder - Stromtrooper Forum : Suzuki V-Strom Motorcycle Forums
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post #1 of 27 Old 03-31-2012, 10:01 PM Thread Starter
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Question Why 2 plugs per cylinder

why 2 plugs per cylinder?
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post #2 of 27 Old 03-31-2012, 10:08 PM
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why 2 plugs per cylinder?
For emissions reasons. It assures a more complete burn of the lean mixture.

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post #3 of 27 Old 04-01-2012, 10:16 AM
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Dual Plug conversions were popular with the BMW airhead flat twins. More complete combustion.

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post #4 of 27 Old 04-01-2012, 10:30 AM
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In laymens terms the second plug is used to insure the mixture in that cycle has a better chance of being ignited. With the lean mixtures ( especially at cruise ) it is possible that the mixture in the area of one of the spark plugs is too lean to fire ( or sometimes fire but "die out" because mixture ratio won't promote a flame front ). The other plug likely has a better chance of igniting the mixture. They also promote a better quality of burn. Two flame fronts can burn the mixture quicker and that can eliminate detonation. Not all of this is for emissions, although you can imagine what unburned fuel does for emissions, but the two plugs can make more peak power. Two plugs per cylinder were originally considered a "band aid" for a poorly designed combustion chamber. With the emissions and fuel economy pressures on engines now, the two plug design is being utilized from the start of engine design instead of being a "band aid".

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post #5 of 27 Old 04-01-2012, 10:34 AM
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Because three won't fit. Sorry, I couldn't resist.

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post #6 of 27 Old 04-01-2012, 10:57 AM
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Dual Plug conversions were popular with the BMW airhead flat twins. More complete combustion.
I did the conversion on my R90S. There was a time during the conversion to unleaded fuel when premium was not available. Dual plugging allowed the use of regular because two flame fronts shortened the time to complete combustion requiring retarding the spark timing significantly.

Pat- 2007 DL650A was ridden to all 48 contiguous states. I didn't quite make it to 17,000 miles on the 2012 DL650A.
Nicknames I use to lessen typing, Vee = 2002-2012 DL1000s. Vee2=2014-2016 DL1000s. Wee = 2004-2011 DL650s. Glee = 2012-2016 DL650s
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post #7 of 27 Old 04-01-2012, 11:06 AM
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Quote:
Originally Posted by greywolf View Post
during the conversion to unleaded fuel when premium was not available.
you didn't have Amoco stations in your area ?

the 83 Nissan King Crab truck I had, had 2plugs/cylinder



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post #8 of 27 Old 04-01-2012, 11:16 AM
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you didn't have Amoco stations in your area ?
I regularly rode out of my area and even Amoco did not convert all their stations from leaded premium to unleaded premium immediately. Believe me, finding premium was impossible in many locations for quite a while. People bought bottles of octane booster to get them through the transition. Those with unhardened valve seats pretty much lost their engines. Shops did a big business in dual plugging and hardened valve seat replacements for a while.

Pat- 2007 DL650A was ridden to all 48 contiguous states. I didn't quite make it to 17,000 miles on the 2012 DL650A.
Nicknames I use to lessen typing, Vee = 2002-2012 DL1000s. Vee2=2014-2016 DL1000s. Wee = 2004-2011 DL650s. Glee = 2012-2016 DL650s
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post #9 of 27 Old 04-01-2012, 12:35 PM Thread Starter
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band aid for not having high enough octane fuel

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Originally Posted by realshelby View Post
Two flame fronts can burn the mixture quicker and that can eliminate detonation. Two plugs per cylinder were originally considered a "band aid" ... ...
it may not completely eliminate detonation but, it helps. (not quicker) helps by igniting all fuel at the same time. so as there will be no small deposits of unburnt fuel on the outside edge of the flame, which can ignite on their own due to heat & pressure and cause detonation. its a "band aid" for not having a high enough octane fuel.
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post #10 of 27 Old 04-01-2012, 01:21 PM
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Igniting all the fuel at at the same time is the definition of detonation. Two flame fronts allow retarding the timing and reach all the points in the combustion chamber before a distant point would self ignite from heat and pressure. They also burn the very lean mixtures in modern engines more completely. It's not a band aid but a very efficient combustion chamber design.

Edit: I later realized I need to say the above is mostly about symmetrical dual plugging. Suzuki just added a plug at the periphery of the combustion chamber. It is a band aid to meet emissions regulations and I was disappointed the plugging was not done symmetrically. I guess that would be difficult in a four valve combustion chamber.

Pat- 2007 DL650A was ridden to all 48 contiguous states. I didn't quite make it to 17,000 miles on the 2012 DL650A.
Nicknames I use to lessen typing, Vee = 2002-2012 DL1000s. Vee2=2014-2016 DL1000s. Wee = 2004-2011 DL650s. Glee = 2012-2016 DL650s
See https://www.stromtrooper.com/general...nicknames.html

Please vote in the poll on what Strom(s) you have at https://www.stromtrooper.com/informa...-you-have.html

Last edited by greywolf; 04-01-2012 at 01:32 PM.
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