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Plug indexing and flame propagation #744130
08/02/18 8:07 pm
08/02/18 8:07 pm
Joined: Aug 2001
Posts: 2,145
Oztralia
R
Rohan Offline OP
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Rohan  Offline OP
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Joined: Aug 2001
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Oztralia
Some bizarre? posts over on another norton forum not so far away.

Now, everyone knows that some supercharged engines need to be very careful with their gas flow and spark arrangements - big supercharging ratios and high gas speeds and lotsa liquid fuels can 'blow' the spark out.
One counter to this, in some engines, is to 'index' the plug, such that the earth post on the spark plug tip protects the spark from the incoming rush of gases.
Supercharging has been around now for oh about a century or so, so this is not exactly anything new.
If you've ever seen a top fuellie in action, they have some very intricate preparations to get them to perform like that.

Also, some experimental engines in the past had little glass windows cut into the combustion chamber, to directly observe the combustion process.
Until they carbon over, which generally happens rather promptly unfortunately.
What was observed was that the flame front does occur "like a prairie fire".
And twin plugging a head involves 2 flame fronts, which need some care in arranging so the merge occurs gracefully.

And, a "percussive explosion" is not what is needed at all, that is detonating or pinging or knocking, bad bad bad.

Now, I've even seen inside such a glass window into a cylinder head, and while it all happens in the twinkling of an eye,
a high speed movie camera can catch the action. ( a general movie camera only gives 24 frames per second,
so all the combustion can happen between individual frames !!

As for these statements.
"Combustion starts when an oxygen ion collides with a carbon or hydrogen ion, and if the collision has sufficient energy, then there is a reaction. The ions are randomly travelling in three dimensional space so the presence of the tang and its' position in space becomes mostly irrelevent."

This sounds like what happens in a diesel, only I don't know where any "ions" would come from, atoms and molecules are still most definitely involved

"I would relegate plug indexing to the status of voodoo magic, and I would be very surprised if anyone could show dyno data to support the concept."

Seems this "voodoo" has some very sound scientific basis.....


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Re: Plug indexing and flame propagation [Re: Rohan] #744270
08/04/18 1:13 am
08/04/18 1:13 am
Joined: Oct 2001
Posts: 247
Monclova
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sloppyoil Offline
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sloppyoil  Offline
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Posts: 247
Monclova
Not Vodoo, use it all the time even on stock engines. Used to be quite the thing in the old days on Pure stock cars and stock. Im sure there are all kinds of explanations, answers, theories, and self proclaimed experts. But, the way I was taught, and none other than by the likes of Eric and Jan Riedle, diamond racing engines was to adjust the position of the spark plugs by use of indexing washers , that come in various thicknesses ( Comp Cams sell them) to position the plug as close as possible to the exhaust placement of the exhaust or header outlet. That's it, works great and does make a difference the way the plug burns and allows for a precise reading of the plug on all eight cylinders or two if on a BSA . Now with todays flame thrower ign systems, MSD, HyFires, crank triggers etc, well IDK. But in the old points systems and GMs K66 this is what we did. I index my plugs in my BSAs and Triumphs, try it you might like it. P.S. easier on English twins than on a camaro with a rat.

Re: Plug indexing and flame propagation [Re: Rohan] #744278
08/04/18 2:16 am
08/04/18 2:16 am
Joined: Mar 2006
Posts: 1,326
Magnolia, TX
htown Online content
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htown  Online Content
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Joined: Mar 2006
Posts: 1,326
Magnolia, TX
My question was how to make sure the plug is proper tightness. Sloppyoil answered it with indexed washers of various thicknesses. Sounds like a ton of trial and error. I've got better uses for my limited time left on this planet.

Last edited by htown; 08/04/18 3:32 pm.

1978 Bonneville T140E
1974 Trident
1970 BSA Thunderbolt
1971 Norton Commando
1972 Norton Commando
1973 Norton Commando
1974 Norton Commando
2004 XL 1200R Sportster

Everything will be alright in the end. If its not alright, its not the end.
Re: Plug indexing and flame propagation [Re: Rohan] #744338
08/04/18 12:09 pm
08/04/18 12:09 pm
Joined: Oct 2012
Posts: 3,833
Running from demons in WNY
Hillbilly bike Online content
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Hillbilly bike  Online Content
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Posts: 3,833
Running from demons in WNY
Yes, used to be the thing to do in auto drag racing....But not so much any more for whatever reasons....If it makes a difference on the track or the road then it's worthwhile..


I ride dinosaurs....
Re: Plug indexing and flame propagation [Re: Rohan] #745030
08/09/18 9:42 pm
08/09/18 9:42 pm
Joined: Aug 2001
Posts: 2,145
Oztralia
R
Rohan Offline OP
BritBike Forum member
Rohan  Offline OP
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Joined: Aug 2001
Posts: 2,145
Oztralia
Mention of dual plugging brought out the pundits.
Who seem to have missed that dual plugs builds combustion chamber pressure much earlier,
SO requires less ignition advance.

Phil Irving wrote about this, when dual plugging became popular in the 1930s with race bikes.
The problem then became if one plug fouled, the bike slowed a bit because of insufficient ignition advance
(only running on one plug), and the rider then faced the dilemma of stopping to change both plugs
(since you don't know which one it wil be) or continuing on at a reduced rate.
Twin plugging popularity died out....


Moderated by  Dave Comeau 


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