How to index spark plugs.

[Liv]

So yesterday the indexing washers came for the Metro. As with almost everything in this car, I expected to find near original equipment condition plugs in need of replacement. Oddly, it was the one thing that had been replaced. The plugs were dated 2006, and were Bosche. I've never heard good things about Bosche spark plugs, and as I was pulling them I marked their alignment with a Sharpie. Every one of them was aligned with the electrode shielding the valve. One thing I can say for the plugs, is they were manufactured uniformly. In essense, these spark plugs were "aimed" towards the wall of the head, rather than the fuel mixture. Exactly what indexing is meant to prevent.

What is indexing? Well it's just that, aiming the open end of the spark plug away from the walls of the combustion chamber and towards the center of the valves. Some engines produce significantly more power by indexing, some don't. It only costs a few washers, and a couple extra minutes, so the concensus is if you're going to change your plugs, then do it right, and index them.

It's really simplier than it sounds. Basically just like the plugs I removed, you mark the open end of the spark plugs with a Sharpie. Install and see where it lines up. If it's "straight up" or within 30 degrees of 12 o'clock then you're indexed. If they align differently, then by adding a indexing washer (they come in varying thickness) eventually you get the correct position.

Patience is a virtue, but I managed indexing my three cylinder in under 20 minutes. Simply, try it with no indexing washer, then if incorrect add the thinnest one, and move up from there.

When done, you should have a smoother running more balanced engine that could produce more horsepower and better MPG.
I'll report back in a week or so, to see if I record any difference on my fuel log, but I already have a sense of contentment knowing I'm doing all I can to make my engine as happy as possible.

I know there is some argument to whether indexing actually works, but I have seen dyno numbers, and drag times to suggest it does. Need further proof? Honda engineers color code specific spark plugs on the Honda Insight to make that engine "indexed", which allows the vehicle to produce the high gas mileage it does.

Think of it like this. There's a bomb in the room you're in right now, and it's sitting by the wall. It's about to explode. If there's nothing blocking its way, it will explode and radiate out from where it explodes out into the room killing everyone. On the other hand, if you were to run over to the bomb and use your body as a shield, you would, in fact absorb some of the blast and prevent the bomb from radiating (at least to the same degree) out into the room. In the combustion chamber, you, are the electrode, shielding the explosion in the room (combustion chamber). The difference is we want the big explosion, we want everyone to die. So by turning the electrode to the optimal position through indexing, you can blow up all those evil air and fuel molecules in the engine. Death, destruction, mayhem on the inside, yet on the outside you might be saving the world...

I'm all about saving money (gas), and maybe even the enivornment to boot. If twenty minutes of time isn't worth the benefits of both, than it's certainly worth my clear conscience.

[A Person]

Here's what NGK have to say about indexing ...

Indexing refers to a process whereby auxiliary washers of varying thickness are placed under the spark plug's shoulder so that when the spark plug is tightened, the gap will point in the desired direction.

However, without running an engine on a dyno, it is impossible to gauge which type of indexing works best in your engine. While most engines like the spark plug's gap open to the intake valve, there are still other combinations that make more power with the gap pointed toward the exhaust valve.

In any case, engines with indexed spark plugs will typically make only a few more horsepower, typically less than 1% of total engine output. For a 500hp engine, you'd be lucky to get 5hp. While there are exceptions, the bottom line is that without a dyno, gauging success will be difficult.

Think of it like this. There's a bomb in the room you're in right now, and it's sitting by the wall. It's about to explode. If there's nothing blocking its way, it will explode and radiate out from where it explodes out into the room killing everyone. On the other hand, if you were to run over to the bomb and use your body as a shield, you would, in fact absorb some of the blast and prevent the bomb from radiating (at least to the same degree) out into the room. In the combustion chamber, you, are the electrode, shielding the explosion in the room (combustion chamber). The difference is we want the big explosion, we want everyone to die. So by turning the electrode to the optimal position through indexing, you can blow up all those evil air and fuel molecules in the engine. Death, destruction, mayhem on the inside, yet on the outside you might be saving the world...

Not really ...

It's not like a bomb in a room - it's more like a room full of gas. It doesn't matter where in the room the match is lit, the flame will propagate throughout the room. The electrode doesn't shield the explosion, which occurs round it, it's more that the flame has to propagate round the electrode to ignite all the fuel - to use your analogy, if you (as a gas molecule) can run faster than the flame you could get out of the door (exhaust valve) before getting burnt.

Flame propagation speed is between 3 and 10 m/s so it can get everywhere inside a 100mm dia cylinder in one or two milliseconds, but then again that's all the time it has - at 6,000 rpm the engine revolves once every 10ms

Anyway, have fun experimenting, but I doubt you'll save enough fuel to get your money back for the cost of the washers

[A Person]

Champion say much the same thing ...

Indexing

Typically used by racing tuners, indexing refers to a process whereby auxiliary washers of varying thickness are placed under the spark plug's shoulder so that when the spark plug is tightened, the gap will point in the desired direction. However, without running an engine on a dyno, it is impossible to gauge which type of indexing works best in your engine. While some engines may respond to the spark plug gap open to the intake valve(s), others may make more power with the gap pointed toward the exhaust valve(s). In any case, engines with indexed spark plugs will typically make only a few more horsepower at best, typically less than 1% of total engine output. While there are exceptions, the bottom line is that without a dyno, gauging success will be difficult.

In newer multi-valved motors, the spark plug location is increasingly being relegated away from the center of the cylinder head off toward the edge of the combustion chamber. In these situations, a non-indexed plug can be pointing at the cylinder wall which may only be 10-14mm away. The advantages of indexing would certainly be increased in these types of motors.

As used in some Hybrid engines, indexing is the same process as described above in which the spark plug gap has been placed in the direction of the intake/exhaust valves. However the use of indexing washers to achieve that location is not necessary as the starter threads on these spark plugs have already been cut so that when installed and properly torqued, they will already be facing the intake/exhaust valves. In these situations please defer to all manufacturer instructions and special requirements regarding plug selections and any possible plug markings or special indications of cylinder location/placement.

[Liv]

Spark plug lottery, here I go...

I'll post MPG results in a week or so.