Spark Plug Indexing. What is your preferred method?

Carl Balzer

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I've been doing a lot of researching. The point of indexing your plugs is to position the ground so that you can achieve the most efficient burn. The most accepted way is to position the opening towards your intake ports where the fuel is coming in. In the n54, wouldn't we want to position them towards the injectors, but I've read that sometimes this causes spark blow out. Anyone have some insight?
 

dyezak

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I tend to believe engineers are meticulous people, and there are rarely details that aren't purposeful. This is 100x as true if you notice a trend. Notice, all the pics of engine diagrams or cutaways where a DI engine has a spark plug with a single ground electrode they always place the gap towards the injector.

gasoline_direct_injection_buick36v6.jpg


ma0516-d01-Ford-Ecotech-GDI-Injector-Placement.jpg


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D4D4S_DirectInjection_30Jan17-3-626x630.jpg
 

doublespaces

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If you follow the torque spec, and assuming your threads are in good shape, isn't this already dictated by where the threads begin? Once seated there are only a set number of turns and unless you've got some other issues I think to a large degree the spark plug will always point in the same direction, no? Unless there are plugs where the electrode portion can be rotated that I am not familiar with?
 
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dyezak

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If you follow the torque spec, and assuming your threads are in good shape, isn't this already dictated by where the threads begin? Once seated there are only a set number of turns and unless you've got some other issues I think to a large degree the spark plug will always point in the same direction, no? Unless there are plugs where the electrode portion can be rotated that I am not familiar with?

Not at all. Maybe if you were dealing with an OE plug with a single ground electrode where the OE specified the thread start location in relation to the ground electrode. But our OE plugs are multi-prong. And most people are using generic NGK plugs. How does NGK create a plug that indexes correctly for an N54 DI engine where you want the gap pointed at the injector which is (for sake of argument) 10deg from the thread start....but have that same plug fit a whole different engine with a different index?

That's where indexing washers/spacers come into play.
 

doublespaces

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Not at all. Maybe if you were dealing with an OE plug with a single ground electrode where the OE specified the thread start location in relation to the ground electrode. But our OE plugs are multi-prong. And most people are using generic NGK plugs. How does NGK create a plug that indexes correctly for an N54 DI engine where you want the gap pointed at the injector which is (for sake of argument) 10deg from the thread start....but have that same plug fit a whole different engine with a different index?

That's where indexing washers/spacers come into play.

Yes, aftermarket plugs I didn't really consider that.
 

Xm-n54

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This video does a good job of explaining how to index your plugs and also gives some info on which way to index as well.


I keep hearing mixed views on which way to face the spark though. Seems more common to face exhaust valves rather than injector and avoid spray from injector.
 

JOEinSD

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Hmm interesting. I’ve never thought about this myself. Definitely something to consider, I suppose. Thanks for bringing it up!
 

BOosted 335i

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you can always but few sets of ngk plugs and test fit then till you find the 6 that open pointing toward the injector and return the rest :)
 

Twisted Tuning

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I've been doing a lot of researching. The point of indexing your plugs is to position the ground so that you can achieve the most efficient burn. The most accepted way is to position the opening towards your intake ports where the fuel is coming in. In the n54, wouldn't we want to position them towards the injectors, but I've read that sometimes this causes spark blow out. Anyone have some insight?

I just had this very conversation with someone on Facebook. Can't remember if it was you or someone else. But generally speaking, the open side of the plug is best to face the Intake ports. I've done some (non-scientific) testing through the years and when it comes to DI you need to take into account the ultimate direction that the injector is spraying.

On the N54 i've seen better idles and less studdering with the plugs indexed towards the intake ports. But on other DI engines, i found better results indexing towards the exhaust valves away from the injector. The later was mainly due to the positioning of the injector pretty much firing DIRECTLY at the plug face. And seemed to increase the chance of plug fouling when spraying a lot of fuel. On the N54, the injector points straight down. So plug quenching is theoretically decreased wehn spraying a lot of fuel. so indexing toward the injector/intake valves seemed to give the best results.


If you follow the torque spec, and assuming your threads are in good shape, isn't this already dictated by where the threads begin? Once seated there are only a set number of turns and unless you've got some other issues I think to a large degree the spark plug will always point in the same direction, no? Unless there are plugs where the electrode portion can be rotated that I am not familiar with?

Not at all. Maybe if you were dealing with an OE plug with a single ground electrode where the OE specified the thread start location in relation to the ground electrode. But our OE plugs are multi-prong. And most people are using generic NGK plugs. How does NGK create a plug that indexes correctly for an N54 DI engine where you want the gap pointed at the injector which is (for sake of argument) 10deg from the thread start....but have that same plug fit a whole different engine with a different index?

That's where indexing washers/spacers come into play.

OEM or aftermarket, threads never start and end at the same spot. And just because a plug is OEM to a car from the manufacturer. Best believe they are just rebranded or made by one of the major spark plug makers and also were made to fit other engines so the same still applies. Threads start and stop at different places which will affect the index position.

The very best way to index plugs is to buy double you need and try to get them indexed how you want without spacers. because spacers affect plug cylinder depth.


EDIT: indexing plugs for me, was and is never done for power gains, but mainly to promote better combustion and reduce the chance of misfire.
 

fmorelli

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IThe very best way to index plugs is to buy double you need and try to get them indexed how you want without spacers. because spacers affect plug cylinder depth.
I like this recommendation. I never realized the plugs are not made in a repeated fashion - that is that the ground is arbitrary to the thread cut. I guess I have to go look at a plug set. If one wants to minimize depth impact, making spacers is necessary which is also a PITA and time consuming. Thanks for this idea - I'll take a look at some plugs.

Filippo
 

iminhell1

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My personal experience is that the design of the plug plays some part in if indexing works and how well.

Surface fire - no way to index (I doubt you guys will ever use them or have ever used them in a auto application. I tried them in a built Conquest with fair results)
Projected tip - The only direction you don't want is the ground strap blocking the direction of the fuel spray. Straight on, off-center or similar will make no discernible difference.
Recessed tip - These seem to be more susceptible to directionality. I think it has something to do with the air/fuel not self propagating up into the plug. The ground strap gives a path to help with that and to do so well has to fast the source.
Multiprong - I wouldn't say directionality changes have any impact, but the tip style is still relevant, ie the ground shouldn't directly block the tip if recessed.

There may also be some degree of cooling that plays into indexing and maybe the cooling allows just a little more current to jump. But I've never seen any talk about it, never looked either.


And far as any plug, or all plugs, starting the threads uniformly; I've never looked into it. But I don't think any plug from anyone is 100% uniform. And even if they are if you have perfect indexing then the head also needs the be perfect and that I know I've never seen.
What I'll do is run a marker strip down the plug and put the same plug in each hole. I'll always find that it will rarely point the same direction in all holes. Oddly enough though it seems there will be 2 that are quite similar.
 
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