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Indexing spark plugs on a 4.0 SOHC

aldive

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In my inexhaustible pursuit of superior gas mileage (http://www.explorerforum.com/forums/showthread.php?t=44372&highlight=quest ) I have made many mods to my truck, some performed well while some did not. I recently decided to give an old racer’s trick an evaluation on my ’99 4.0 SOHC (http://www.explorerforum.com/forums/showthread.php?t=137531 ). The trick is indexing the spark plugs.

Pray tell, what is this indexing? In essence, the concept of indexing is to orient the spark plug so the gap is facing the center of the cylinder, slightly toward the intake valve ( some say toward the exhaust valve ). The logic is, as the piston approaches top dead center, the air/fuel charge is being compressed. The air/fuel charge is accelerated toward the area of the spark plug. Consequently, the spark emanating from the plug should be orientated to create the best possible flame front. When viewing our Explorer’s side-gap spark plug, one will observe the electrode can actually block the flame process. Conversely, if the electrode gap faces the advancing air/fuel charge, it stands a improved chance of optimally igniting a flame front.

My interest in this venture is the theoretical boost in gas mileage due to a more efficient ignition process; the increase in HP, albeit small, is a welcomed windfall.

Indexing the spark plugs is a time consuming and tedious task. Is it worth it? We shall see in the upcoming week. Remember, since my interest in this project is strictly gas mileage, consequently, a before and after dyno test will not be conducted.

I used indexing washers to align the plugs. These are soft copper washers of various thicknesses ( 0.010'', 0.021'', 0.032'' ).

The first step in the indexing process is to make a mark on the spark plug ceramic with a black Magic Marker, oriented with the gap. After installing the plugs ( to 10 ft pounds ) and noting the position of the mark, the plugs were removed and indexing washers of varying thickness ( trial and error ) were added to allow the gap to point in the desired location. This was accomplished by adding. The plugs were tightened to 10 ft pounds and the location of the index mark checked for position. Perfect alignment evaded me, but it was close enough for government work.

This project took about 2 1/2 hours and was a major pain in the arse, however, the only cost was the indexing washers Moroso (http://www.moroso.com/default.asp ) 71900 - Spark Plug Indexing Washers
Obtained from Jegs [ http://www.jegs.com/webapp/wcs/stores/servlet/product_10001_10002_39232_-1 ] for $15.99 and of course my time.

Upon cranking there was no difference in start up or idling compared to conditions prior to indexing. A test drive through the neighborhood showed no power difference nor was any expected. A 40 mile highway run confirmed.

A road trip to Atlanta is scheduled in a few days during which gas mileage data will be compiled. The numbers shall be reported on my return.
 

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Donner

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In order for the readings to be 99.99% accurate, you will need to use a new air filter and be certain the air pressure in the tires is as precise as possible, correct? Are there other items that could affect the outcome of your research?
 




CDW6212R

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FYI, Summit sells an indexing tool that makes the job easier. I bought the tool this Summer, but I wasn't planning to actually use it any time soon.

With the tool you mark each plug before you take it out. After that use the tool to discover the needed washer, and then install the plug. I hope that it helps, good luck.
 




aldive

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FYI, Summit sells an indexing tool that makes the job easier. I bought the tool this Summer, but I wasn't planning to actually use it any time soon.

With the tool you mark each plug before you take it out. After that use the tool to discover the needed washer, and then install the plug. I hope that it helps, good luck.

Sounds like a time saving device.
 




CDW6212R

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I was going to ask you how it worked, but it sounded like you did it the other way. Next time though, yes?
 








CDW6212R

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That's nicer yet, mine I think is a Summit part, just under $10, black with no marks on it. I thought that when I got to a supercharger that I would have a good reason to do the indexing.
 




crankshop1000

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Indexing has been proven to be a waste of time.No increase in MPG or HP and no effect on emissions.Tried it on my 2 stroke race engines.
 




brianjwilson

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I would think that any possible (very) small increase would be impossible to measure on open road, due to variances in tires pressures, wind, temp, pressure, humidity, weight, etc etc.
Cool concept but with all of the fuel/air compressed in there I can't see how there would be any measureable difference in efficiency by trying to 'aim' the spark, when it's only jumping a gap.
 




aldive

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After 4 days of in town driving, I have observed no differences in driveability. However, I have not checked gas mileage yet.

I leave in the morning for a 1500 mile road trip. I shall have gas mileage data upon my return next Tuesday.
 








CDW6212R

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Al, my tool was a Moroso part, I saw it yesterday again.
 




aldive

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The first gas mileage data after indexing the spark plugs is in ….

The first leg of the trip, 515 miles, average speed 68.5 MPH ( GPS determined ) netted 34.6 MPG whereas the return leg ( 501 miles, 67.7 MPH average speed netted 34.8 MPG. The trip average was 34.7 MPG.

The above compares to 34.3 MPG ( average of several previous Atlanta trips ).

Indexing netted an average of 0.4 MPG.

No improvement in start up or perceived power was noted.

Perhaps moving the index more toward the exhaust or toward the intake valve could produce better results. I may give this a go sometime in the future.

Was it worth it? Maybe;time will tell. Further testing is scheduled.
 




daves97sport

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the concept of indexing is to orient the spark plug so the gap is facing the center of the cylinder, slightly toward the intake valve ( some say toward the exhaust valve )
Theoretically, the ground electrode should be closest to the side of the cylinder wall, as with these engines, the plug is offset in the combustion chamber. This would prevent the electrode from blocking the flame propagation into the largest chamber area. Skewing this one way or the other would only be effective if the shape of the chamber is that there is a larger area near the intake, or exhaust valves... If you've gotten a 1.15% increase already, I'm not sure how you could measure a difference by skewing, unless you would have the technology to visibly see how the flame spreads.
Indexing has been proven to be a waste of time.No increase in MPG or HP and no effect on emissions.Tried it on my 2 stroke race engines.
On most 2 stroke engines, the plug is centered in the combustion chamber, as is the case with most dual overhead cam engines where the plugs are in through the top of the valve cover. Indexing would not be as effective being centered unless the shape of the combustion chamber is that the electrode would block the flame from the "larger" area, or if the electrode would be interfering with the incoming air/fuel mixture from the intake valve
Just when I though I'd seen it all from you Al, you come up with one more way...
My hats off to you and THANKS for the efforts!!!
 




35Remmy

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Does that Accel indexing tool make the job that much easier? Or does a sharpie or a zip tie do just as well?
 




joefnh

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The tool just helps you pick the correct washer based on the number of degrees of rotation that you are off on the spark plugs threads.

My concern for that tool is that it only tests the threads on the plug, not the threads on the cylinder head. The combination of those 2 threads starting points relative to the spark plug will actually determine what washer is needed to properly index the plug.

That is why I used the zip tie, it let's me know the final position of the spark face which is what counts anyway. If you use the zip tie be sure to pull it tight so that it cannot be bumped out of position easily.

See the thread:

http://www.explorerforum.com/forums/showthread.php?t=213274



--Joe
 




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