Best Plug Positioning?

Gavin

Specialist
Apr 23, 2018
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Montauk,NY
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e92 Coupe
Looking for some help,
From picture drawing,would the open side facing the injector be the best or optimal for burn?So that would be 12 O'Clock position.I have bunch of 95770 plugs and most of then are between 10 & 2 where the open end of plug is from the injector,some are 4-7pm.Since i have them just want optimal burn,thanks.
 

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fmorelli

Major General
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Aug 11, 2017
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I dont think the gains are worth the effort but..take a look
... and someone can prove otherwise. That said, I would imagine if free gains were there, they'd be more complete burn as well, which means better emissions - I would imagine BMW would have machined those holes in such a manner that their specified plug would point that way +/- whatever the variance might be for torquing down the thread and washer compression.

Filippo
 

iminhell1

Sergeant
Jun 17, 2018
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... and someone can prove otherwise. That said, I would imagine if free gains were there, they'd be more complete burn as well, which means better emissions - I would imagine BMW would have machined those holes in such a manner that their specified plug would point that way +/- whatever the variance might be for torquing down the thread and washer compression.

Filippo



Or maybe they went the easy route with a multi-prong design.
 

Optigrab

Corporal
Sep 19, 2018
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If you are using port it might matter but the DI injector is right next to the plug and the engine is high compression
 

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Cheezy

Lieutenant
Nov 7, 2016
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Toledo Ohio
@carlbalzer, David Shoup, Nick Marinos and myself have all debated this amongst ourselves heavily. The problem with @fmorelli theory of the hole in the block being cut one way is that the threads in every spark plugs and is different so that would be impossible to control due to that variable. The BMW DI engines use a piezo style injector that sprays in a cone shape over the cylinder. You want ignition to occur downward, not forwards, backwards upwards then downwards. So try to make your plugs face the injectors
received_10102495445374512.jpeg
 

fmorelli

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The problem with @fmorelli theory of the hole in the block being cut one way is that the threads in every spark plugs and is different so that would be impossible to control due to that variable.
Sorry I'm dense today. Can you explain this? Are you saying that the threads are not cut in the same orientation relative to the electrode ground, from one spark plug to the next?

Filippo
 

Optigrab

Corporal
Sep 19, 2018
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Found this in the engine management docs. It would seem the gas is atomized and swirled around a good bit before it is ignited

The piezo-injector is integrated together with the spark plug centrally between the inlet
and exhaust valves in the cylinder head. This installation position prevents the cylinder
walls or the piston crown from being wetted with injected fuel. A uniform formation of the
homogeneous air/fuel mixture is obtained with the aid of the gas movement in the combustion
chamber and a stable fuel spray cone.

The gas movement is influenced on the one hand by the geometry of the intake
passages and on the other hand by the shape of the piston crown. The injected fuel is
swirled in the combustion chamber with the boost air until a homogeneous mixture is
available throughout the compression space at the point of ignition
 

ShocknAwe

Captain
Jan 24, 2018
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Sorry I'm dense today. Can you explain this? Are you saying that the threads are not cut in the same orientation relative to the electrode ground, from one spark plug to the next?

Filippo

Threads from one plug brand to next aren't necessarily the same in terms of the start of the first tooth. So as you tighten the ground would end up in a different orientation relative to the injector.
 

pdxbimmertech

Lurker
Dec 18, 2017
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Portland, OR
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2008 E92 335i 6 spd
Went to some BMW training for work last weekend and the indexing mystery was explained for the single electrode plugs in modern BMW engines. I know the indexing thing was discussed in another thread about a month or so back. The plugs are made with precision robotic equipment and they are able to see where the threads start, where the electrode is and can determine the proper thickness for the sealing washer that seals against the cylinder head when torqued down. The relationship of threads, electrode and the washer thickness is supposed to get the electrode in the correct spot to achieve the proper combustion and make the plugs "indexed". This explains why the single electrode plugs don't have a "crush" style sealing washer and have a much more solid feeling when they are torqued down.
That being said, it's very likely running N20, N55 or S55 plugs etc that the electrode may be facing a totally random way in an N54.
 
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BOosted 335i

Sergeant
Jun 1, 2017
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New Jersey
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Threads from one plug brand to next aren't necessarily the same in terms of the start of the first tooth. So as you tighten the ground would end up in a different orientation relative to the injector.
I just changed my plugs and the threads are all the same orientation in the head but yes the plugs are not all the same,so just buy few sets to match them all up.