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indexing spark plug?

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whats the correct way to orient the plug for a single cylinder 2 stroke?

ive done it for my race cars, but wondering if its worth it for dirt bikes?

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there is not benifit in indexing a carbed 2 stroke dirtbike motor.

the only time a plug needs to be indexed is when it is a direct injection motor. even an EFI motor dosent need it.

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there is not benifit in indexing a carbed 2 stroke dirtbike motor.

the only time a plug needs to be indexed is when it is a direct injection motor. even an EFI motor dosent need it.

+1 Indexing isn't worth it. :smirk:

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correct me if i 'm wrong but isn't indexing a spark plug when you put the open side of the plug facing towards the intake?

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yeep.the BRP e-tecs NEED the plug to be indexed within 35* of the injector or they will run like shit. also BRP's old vertion of the e-tecboat motors(ficts) needed the plug indexed.

the other i know off by hart is merc. opti-max D.I's need the plug indexed as well.

thats the only applications i can think of off of the top of my head that absolutly need the plug indexed.

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+1 Indexing isn't worth it. :smirk:

On bikes the spark plug is centered over the piston.....On most cars the plug sits to the side of the cylinder......So you would want the opening to be up...

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Not in every case. The core theory behind indexing is that the ground electrode is assumed to be of the standard type consisting of a metal bridge extending from the plug shell up and over the center electrode of the plug, and that the ground electrode should be placed so as not to occlude the exposed spark from the fuel air mix moving past it when ignition occurs.

The whole question then hinges on the specific dynamics of the gas flow within the combustion chamber at the time of ignition, not when the valves or ports are open, and this will obviously be different with every engine. Some respond to it, and with others, it makes no difference.

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On bikes the spark plug is centered over the piston.....On most cars the plug sits to the side of the cylinder......So you would want the opening to be up...

Depends on the car. :smirk:

Almost all late model vehicles, especially 4 valve engines, have the spark plug directly in the center of the combustion chamber. 2 valve engines are few and far between, Ford axed all their 2V engines and went with a 3V, the plug is now in the center. The Chevy V8's are the only exception I can think of and that is because the valve size is massive which doesn't allow the plug to be centered.. and because of how the old valvetrain is oriented.

Greyracer is right, the idea to to index the plug so that the ground electrode doesn't shroud the incoming A/F mix but most modern day combustion chambers are designed to have the A/F swirl when entering the chamber so it's pretty much pointless unless your trying to cram every last smidgen that might be there. Even then, you are hoping the swirl takes the A/F to the plug from the direction you orient it.

Who knows, I may be wrong since I haven't spent enough time to prove it myself, but other well known racers told me it's pointless so take the information as you will. I just stick with what I know, electronics! :smirk:

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As I said, the results are going to vary widely with each different engine you try it on, and even with different builds of the same engines. Also keep in mind that the orientation of valves, ports, etc., does not bear directly on the question to any great extent, because what is important is how the FA charge is moving at the moment of ignition. By that time, all the ports have long since closed. There is certainly some residual inertia moving the air charge around and that is influenced by the flow through the open port(s), but there is also the influence of the piston moving up into the combustion chamber, the shape of the head and piston crown, and the rapidly changing overall shape of the whole chamber. What you end up with across the spark plug isn't always as easily visualized as you might think.

The old iron small block Chevy used to be one of those engines that indexing was good for, and the correct orientation was to have the ground away from the exhaust valve. Later, Chevrolet Racing produced several sets of "Bow Tie" head that angled the spark plugs toward the exhaust. This change generally produced about 12HP in engines putting out around 400HP with straight plug heads.

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Depends on the car. :smirk:

Almost all late model vehicles, especially 4 valve engines, have the spark plug directly in the center of the combustion chamber. 2 valve engines are few and far between, Ford axed all their 2V engines and went with a 3V, the plug is now in the center. The Chevy V8's are the only exception I can think of and that is because the valve size is massive which doesn't allow the plug to be centered.. and because of how the old valvetrain is oriented.

Greyracer is right, the idea to to index the plug so that the ground electrode doesn't shroud the incoming A/F mix but most modern day combustion chambers are designed to have the A/F swirl when entering the chamber so it's pretty much pointless unless your trying to cram every last smidgen that might be there. Even then, you are hoping the swirl takes the A/F to the plug from the direction you orient it.

Who knows, I may be wrong since I haven't spent enough time to prove it myself, but other well known racers told me it's pointless so take the information as you will. I just stick with what I know, electronics! :smirk:

The reason I stated most cars...I use to mess alot with small block Chevy....I would mark the spark plugs and sit there with index washers , trying different thicknesses till I got the right one.......On a dyno or a full all out race engine....Yeah it helps.......but for the average engine and the average bike........you would never feel it......

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The reason I stated most cars...I use to mess alot with small block Chevy....I would mark the spark plugs and sit there with index washers , trying different thicknesses till I got the right one.......On a dyno or a full all out race engine....Yeah it helps.......but for the average engine and the average bike........you would never feel it......

I wonder if the new Chevy LS engines respond to it. I know they re-orientated the spark plug to the exhaust port to change this. Have you tried?

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^No I got out of the car stuff.......it just got way to expensive to mess with....All I mess with now are bikes........

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