Indexing spark plugs

[Kev7s]

Just wondering if any one has tried indexing plugs on a dyno, and actual see the results. They claim 5-15 horsepower. Thanks for your time.

[rally]

I index my plugs. Does it make more horsepower, i heard pro and cons. Personally i dont think it does.

[Alaskaracer]

Only real reason to index spark plugs is to gain electrode clearance from the piston......

[4banger]

I'd like to see the dyno results of a side gap plug test.

[Cubic_Cleveland]

Only real reason to index spark plugs is to gain electrode clearance from the piston......

This ^^^^

[engineguyBill]

Only real reason to index spark plugs is to gain electrode clearance from the piston......

This ^^^^

X3!

[Kevin Johnson]

viewtopic.php?t=5093

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.

[Kev7s]

Sorry, did not know it was a repost, thanks for the input.

[Kevin Johnson]

Sorry, did not know it was a repost, thanks for the input.

No, don't be sorry. Many topics are brought up again. I just thought it would be helpful. It appears that there is the possibility of a small effect but that extensive time on the dyno is needed to identify an optimal orientation for a particular combo. People that have spent that time might not be willing to just volunteer it.

[W. Tripp]

There are two ways to index. The first requires that you have a LOT of plugs, and the second uses indexing washers of variable or fixed thicknesses. Using washers changes the chamber volume very slightly, but also reduces the heat range of the spark plug. This can be good or bad. Using indexing washers isn't always about plug alignment, but about cylinder temps.

There are things that do not show up on the dyno, but do show up on the track - for better or worse. I have seen indexing show nothing on the dyno, but show better response and shift recovery on the track in lap times and logged data. I have also seen it do the exact opposite.

On a turbocharged 4-valve 2.3L engine I have used indexing washers to cool off cylinders that wanted to detonate, and were holding back the rest of the engine when I could not offset ignition advance in each cylinder individually. This allowed more ignition advance to be run and and instant 3% more power showed up. I have seen twice this percentage gained on a 572ci blown/intercooled BBC marine engine used for speed runs where 2 cylinders were holding back the rest of the engine.

I have seen indexing plugs allow cruise tuning to be more than 1 full AFR leaner than was possible before indexing without running into lean misfire.

So yes, indexing can help, but it all depends on your engine and calibration. Don't expect a 2-valve chamber, a 4-valve chamber with a single central plug, and a 4-valve chamber with twin plugs, to all act the same, or even two identical engines.

I hope this helps.

[Kevin Johnson]

Would you say that to expect repeatable results that you would need thermocouples located close to the exhaust manifold flange on each cylinder and an inertial dyno? Are there thermocouples available that would allow data acquisition that would be nearly coincident with actual sweep rates?

Would you consider the dynos that can replicate an entire race to be required? Could you work backwards from there and give a fuzzy demarcation of what type of dyno would be less likely to deliver the information needed?

Forgot to ask what minimal increment of radians or degrees testing would be needed or expected to detect a "sweet spot".

[rally]

There are two ways to index. The first requires that you have a LOT of plugs, and the second uses indexing washers of variable or fixed thicknesses. Using washers changes the chamber volume very slightly, but also reduces the heat range of the spark plug. This can be good or bad. Using indexing washers isn't always about plug alignment, but about cylinder temps.

There are things that do not show up on the dyno, but do show up on the track - for better or worse. I have seen indexing show nothing on the dyno, but show better response and shift recovery on the track in lap times and logged data. I have also seen it do the exact opposite.

On a turbocharged 4-valve 2.3L engine I have used indexing washers to cool off cylinders that wanted to detonate, and were holding back the rest of the engine when I could not offset ignition advance in each cylinder individually. This allowed more ignition advance to be run and and instant 3% more power showed up. I have seen twice this percentage gained on a 572ci blown/intercooled BBC marine engine used for speed runs where 2 cylinders were holding back the rest of the engine.

I have seen indexing plugs allow cruise tuning to be more than 1 full AFR leaner than was possible before indexing without running into lean misfire.

So yes, indexing can help, but it all depends on your engine and calibration. Don't expect a 2-valve chamber, a 4-valve chamber with a single central plug, and a 4-valve chamber with twin plugs, to all act the same, or even two identical engines.

I hope this helps.

I buy extra spark plugs. I never use index washers.

[Kevin Johnson]

I buy extra spark plugs. I never use index washers.

Do you have any guidance for the temperature range standard deviation values of different brands/types of plugs?