Spark plug indexing washers...

Old 06-21-08, 08:56 PM
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Spark plug indexing washers...

Help, please! I'm trying to find spark plug indexing washers for 18mm tapered seat plugs, without any luck. They're all over the place for 14mm plugs, tapered and flat, but not for the 18mm. I've looked at Summit and Jeg's, as well as on Moroso's, Accel's, Jacobs', CSR's and Bell's websites, all to no avail. The engine I'm looking to hot-rod is not the most orthodox choice; actually, I'm just trying to milk the most mileage possible from my 4.9-litre-powered '94 Ford F-150. Any ideas? Thanks in advance - Chris
Old 06-21-08, 09:50 PM
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By indexing the plugs, you will not see that much of an improvement vs the time it takes to index the plugs. It will give a little better burn. But for .10 of a hp or .012 better mileage,a good set of plugs is the best way to go..Just my thoughts.
Old 06-22-08, 06:31 AM
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A few years back, I played with a single cylinder ATV and noticed that a spark plug fired best at a certain rotational position. I used high temp grease on the threads to maintain compression.

The results were measured in idle RPM. At one idle setting, the RPM ranged from 2000 down to 1700. The change was audibly different - very obvious. At one full turn out, the RPM wasn't as high, but the peak in that range was still there (but with lower compression).

When I hit the optimum spot, I pulled the head off the cylinder and looked where it was. The arm holding the gap was pointed AWAY from the center of the combustion chamber. This was true for several different manufacture plugs I tried, including 'Split-Fire'.

It occurred to me this is a simple MECHANICAL adjustment, and not one that needs fiddled with as far as Dyno, Meters, and other stuff.

Simply find out what direction the chamber is located (usually TOWARDS the engine when the plug is angled), look at the print on the side of the plugs, and ensure you get the max electrode opening towards the cylinder when tightening it down.

It's not about increased horsepower anymore. It's about SAVING GAS. Burning your fuel more efficiently will increase your gas milage, with fewer trips to the pumps. Mind you it's not a dramatic change....

But a lot of little still makes a lot.

And you're right. Nobody cares about 18mm plugs. Maybe you should first do the 'Visual check' to see if they are needed. Also keep in mind that if the plug comes straight down from the top, there will be no difference.
Old 06-25-08, 03:20 PM
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as far as i know, indexing spark plugs means positioning them in combustion chamber in a specific manner. last i remember, gap should be pointing towards injectors/manifold, with the whole idea being to "spark" directly into the incoming stream of fuel. plus, for regular plugs, some used to cut a grove in the negative elctrode or bevel it at 45 degrees, thus "creating a larger contact surface, thus bigger spark".
well, that was old school ideas. there are several new design plugs out there that give virtually a ball of spark, thus reaching towards fuel stream anywhere in the cc.
not to mention that most modern vehicles have turbulant combustion chamber design, which is geared towards "spiraling" fuel stream inside cc, thus atomizing the mix better, and only then firing the spark, so it does not really matter which way it's pointing in such a cc.
if you want to, you could do Dr. Singh's idea and index combustion chamber, now that's a different animal.

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