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Spark Plug Timing

90FXRS

90FXRS

Junior Member
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I got in the middle of a discussion the other day and thought I would post the highlights here and see what everyone thinks. One guy was talking about how he times the spark plugs so the open side of the center and ground electrodes face the intake port when torqued to 18lbs. He's saying this adds to the efficiency of the engine. I have my doubts on the matter. What are your thoughts?
 
90FXRS said:
I got in the middle of a discussion the other day and thought I would post the highlights here and see what everyone thinks. One guy was talking about how he times the spark plugs so the open side of the center and ground electrodes face the intake port when torqued to 18lbs. He's saying this adds to the efficiency of the engine. I have my doubts on the matter. What are your thoughts?
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This is an old racers trick called indexing,


4. Indexing

This is for racers only !!
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.
This is from NGK, however I have indexed plugs in the past and seem to think it does work
 
The spark plugs in my Dyna and Electra Glides have both been indexed at different times (I bought a kit when I first learned of indexing). I can tell zero difference in performance or mpg. It may be of value in an all out performance engine.
 
Keep in mind it is not bout the torque value of the plug, you mark the open gap of the plug with a sharpie, what you want when you torque your plug is for that line to be in the middle of the valves ( facing the intake ) for a more complete flame front. If it does not line up there are washer kits by Accel to accomplish this
 
A cleaner and more complete burn will perdue more power, more power means more horsepower. Indexing the plugs centers the spark in the proper and most powerful position (between the valves) to create the most efficient and complete burn.

You will see a slight change in the power curve from a indexed engine over a non indexed engine but the more noticeable change will be seen as the HP and cylinders are added, ie 2 cylinders vs 8.
 
Jeff Klarich said:
A cleaner and more complete burn will perdue more power, more power means more horsepower. Indexing the plugs centers the spark in the proper and most powerful position (between the valves) to create the most efficient and complete burn.

You will see a slight change in the power curve from a indexed engine over a non indexed engine but the more noticeable change will be seen as the HP and cylinders are added, ie 2 cylinders vs 8.
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Beg to differ Jeff. Have tested this theory on my own bike with back to back dyno runs. Have also tested the theory on a couple of other bikes; no measureable difference shown on the chart.

Maybe a big deal with 8 cylinder racing motors that rely on WOT for horsepower but in a two cylinder motor that rarely sees 5000rpms, not so much.:s
 
dolt said:
Beg to differ Jeff. Have tested this theory on my own bike with back to back dyno runs. Have also tested the theory on a couple of other bikes; no measureable difference shown on the chart.

Maybe a big deal with 8 cylinder racing motors that rely on WOT for horsepower but in a two cylinder motor that rarely sees 5000rpms, not so much.:s
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I guess will have to agree to disagree Don. A lot smarter people than me have tested indexing and it's affect on power using a dyno to measure the change.

I was referring to your post that indexing won't show on a dyno, that's simply not true.:p
 
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