So I Will Ask a Techie Question ?
- Thread starter teamzr1
- Start date
antijam
CCCUK Member
In my world plug indexing is one of those things for which life is too short. In a race environment where a possible 1% power gain just might make the difference between winning and losing, maybe it's worth the experimentation. NGK seem to sum up the pros and cons pretty neatly.....
"In most engines, performance will improve when the spark plug gap opens toward the intake valve(s). However, without testing different index positions in an engine on a dyno, it is nearly impossible to determine which index increases performance. Indexing spark plugs will typically make only a few more horsepower – usually less than 1% of total engine output. For a 500 hp engine, that’s only 5 hp. It is usually not worth the effort.
There are also drawbacks to indexing spark plugs. When washers are added, the spark plug may loosen if the washers don’t crush properly and hold the torque. Also, if too many washers are added, the firing end of the plug will not be as far into the combustion chamber and performance can decrease."
"In most engines, performance will improve when the spark plug gap opens toward the intake valve(s). However, without testing different index positions in an engine on a dyno, it is nearly impossible to determine which index increases performance. Indexing spark plugs will typically make only a few more horsepower – usually less than 1% of total engine output. For a 500 hp engine, that’s only 5 hp. It is usually not worth the effort.
There are also drawbacks to indexing spark plugs. When washers are added, the spark plug may loosen if the washers don’t crush properly and hold the torque. Also, if too many washers are added, the firing end of the plug will not be as far into the combustion chamber and performance can decrease."
teamzr1
Supporting vendor
In order for any internal combustion engine to function properly, you need three basic things: air, fuel, and spark. Air mixes with the fuel, providing an explosive catalyst. The engine compresses the mixture, which is then ignited when the spark plug fires.
This pushes the piston down, and we now have the miracle of a working engine. Sounds simple in principle, since all you need for that last step is to put the spark plug inside the combustion chamber and make sure it makes a spark, and you're good, right? Actually, the reality is slightly more complicated.
A spark plug sits inside a cylinder via a threaded hole, much like a screw. Virtually all production-level combustion engines function this way, but the process of seating a spark plug in a specific orientation, known as indexing, actually involves multiple steps beyond simply screwing the spark plug in. Still, you can simply screw a spark plug in and be done with it, and the car will run just fine; indexing is only actually useful for extracting slight amounts of performance and extra economy out of your engine.
Does indexing even matter, then?
Generally no, you can usually just screw in and tighten the spark plug, perhaps by using this once-popular tool, and the engine will run fine. There are specific reasons why indexing is performed, one of those is to make an engine run as efficiently as possible.
The potential dangers of improperly indexing outweigh the benefits in many cases. Let's dive in and explore the nuances and what exactly indexing does in your combustion chamber.
A more detailed look at indexing
The tip of a spark plug contains two electrodes separated by a small gap, like having two fingers nearly touching one another. These electrodes are made of different metals, often depending on whether you're using a cheap or expensive spark plug. This allows electricity to jump from one electrode to another, creating the spark.
Much like your finger, however, the topmost electrode sits in a specific orientation, like an archway in a building connected on one side. What this means is that, as you screw a spark plug into an engine, that arm will spin around like a clock.
The purpose of indexing is to make sure that the arm is pointing in a specific direction.
Typically, this process is accomplished by fitting the spark plug with washers of varying thicknesses, meaning it'll only go so far down when it's fully tightened. The thicker the washer, the less rotation you'll have on the arm. The goal, then, is to have the open side of the spark plug facing towards the engine's intake valve or exhaust valve, so that when the air/fuel mixture is introduced, there's no obstruction between it and the spark.
To index a spark plug properly, first locate the intake and exhaust valve on your car, noting which you want to index towards. Next, locate the arm on the end of the spark plug and mark its direction with a marker so you have a reference point.
And finally, seat an indexing washer on the spark plug and tighten it down, comparing the orientation with the mark until you're satisfied. Keep using washers of different thickness to change its final orientation.
Does it really matter?
In a broad sense of the term, yes, indexing spark plugs is a good idea and should be practiced. Beware, however; improperly indexing a spark plug, either by using a washer that's too thick or not tightening it down enough, can result in the spark plug backing out or not being deep enough into the engine to do its job effectively.
Will it kill your engine if you don't index your spark plugs? No, it will not, but it's still better for your engine if you do so.
The inside of an engine is a turbulent, violent place. Air fires out of the intake valve and is ignited in milliseconds, meaning the electrode is quickly and consistently exposed to high temperatures.
If the temperature is sufficiently hot enough, it could ignite the fuel on its own, known as pre-ignition; this is exacerbated when the arm is facing the direction of the heated air.
Moreover, an overly-tightened spark plug runs the risk of hitting the top of the piston, damaging both components. Aside from these, however, it's mostly down to fuel efficiency.
The physics of how air works inside a combustion chamber is its own lengthy discussion, but the short answer is that the chamber is designed with a specific configuration in mind. Deviating from that won't necessarily harm the engine, but it won't be operating at peak efficiency, nor will it if you're running with bad spark plugs.
How to Index Spark Plugs
Step 1: Mark Your Plugs
Before installing your plugs, mark the open end of the ground strap on the porcelain with a permanent marker. This shows where the open side will face once torqued down.
Step 2: Locate the Intake Valve
Reference your engine prints, do some research, or remove your valve covers to find the intake valve at each cylinder. It’s important to know exactly where to point the plug opening, or the effort of indexing isn’t worth it.
Step 3: Install and Check Orientation
Thread the plug into the cylinder head and tighten it with light torque.
Check the mark to see which direction the ground strap faces. The goal is to align it with the intake valve.
Step 4: Use Indexing Washers
If the plug isn’t aligned in the desired position, add or swap out spark plug indexing washers until the orientation is correct.
These precision-stamped washers come in various thicknesses to help fine-tune thread engagement without over-torquing or damaging the tapered seat.
Best Practices
Let’s be clear: Spark plug indexing won’t magically turn your 400 hp street car into a 550 hp monster. But in a finely-tuned motor where every detail counts, indexing spark plugs can give you an edge.
And best of all? It’s cheap and doable. A set of spark plug indexing washers, a few extra minutes of installation time, and a little bit of patience is all it takes to unlock a more efficient burn and a more responsive engine.
If the sparkplug holes are not tapered then using index washers that are made to be crushed when torquing the plug
BUT if the hole is tapered, then user a taper type of index washer like these :
Need beforehand, a torque wrench you know is calibrated
Note :
never leave the torque wrench set to any amount of pressure as sitting unused over time will harm the compressed internal spring, so set it to zero when finished using it
Here is how to do that yourself in a few minutes
This pushes the piston down, and we now have the miracle of a working engine. Sounds simple in principle, since all you need for that last step is to put the spark plug inside the combustion chamber and make sure it makes a spark, and you're good, right? Actually, the reality is slightly more complicated.
A spark plug sits inside a cylinder via a threaded hole, much like a screw. Virtually all production-level combustion engines function this way, but the process of seating a spark plug in a specific orientation, known as indexing, actually involves multiple steps beyond simply screwing the spark plug in. Still, you can simply screw a spark plug in and be done with it, and the car will run just fine; indexing is only actually useful for extracting slight amounts of performance and extra economy out of your engine.
Does indexing even matter, then?
Generally no, you can usually just screw in and tighten the spark plug, perhaps by using this once-popular tool, and the engine will run fine. There are specific reasons why indexing is performed, one of those is to make an engine run as efficiently as possible.
The potential dangers of improperly indexing outweigh the benefits in many cases. Let's dive in and explore the nuances and what exactly indexing does in your combustion chamber.
A more detailed look at indexing
The tip of a spark plug contains two electrodes separated by a small gap, like having two fingers nearly touching one another. These electrodes are made of different metals, often depending on whether you're using a cheap or expensive spark plug. This allows electricity to jump from one electrode to another, creating the spark.
Much like your finger, however, the topmost electrode sits in a specific orientation, like an archway in a building connected on one side. What this means is that, as you screw a spark plug into an engine, that arm will spin around like a clock.
The purpose of indexing is to make sure that the arm is pointing in a specific direction.
Typically, this process is accomplished by fitting the spark plug with washers of varying thicknesses, meaning it'll only go so far down when it's fully tightened. The thicker the washer, the less rotation you'll have on the arm. The goal, then, is to have the open side of the spark plug facing towards the engine's intake valve or exhaust valve, so that when the air/fuel mixture is introduced, there's no obstruction between it and the spark.
To index a spark plug properly, first locate the intake and exhaust valve on your car, noting which you want to index towards. Next, locate the arm on the end of the spark plug and mark its direction with a marker so you have a reference point.
And finally, seat an indexing washer on the spark plug and tighten it down, comparing the orientation with the mark until you're satisfied. Keep using washers of different thickness to change its final orientation.
Does it really matter?
In a broad sense of the term, yes, indexing spark plugs is a good idea and should be practiced. Beware, however; improperly indexing a spark plug, either by using a washer that's too thick or not tightening it down enough, can result in the spark plug backing out or not being deep enough into the engine to do its job effectively.
Will it kill your engine if you don't index your spark plugs? No, it will not, but it's still better for your engine if you do so.
The inside of an engine is a turbulent, violent place. Air fires out of the intake valve and is ignited in milliseconds, meaning the electrode is quickly and consistently exposed to high temperatures.
If the temperature is sufficiently hot enough, it could ignite the fuel on its own, known as pre-ignition; this is exacerbated when the arm is facing the direction of the heated air.
Moreover, an overly-tightened spark plug runs the risk of hitting the top of the piston, damaging both components. Aside from these, however, it's mostly down to fuel efficiency.
The physics of how air works inside a combustion chamber is its own lengthy discussion, but the short answer is that the chamber is designed with a specific configuration in mind. Deviating from that won't necessarily harm the engine, but it won't be operating at peak efficiency, nor will it if you're running with bad spark plugs.
How to Index Spark Plugs
Step 1: Mark Your Plugs
Before installing your plugs, mark the open end of the ground strap on the porcelain with a permanent marker. This shows where the open side will face once torqued down.
Step 2: Locate the Intake Valve
Reference your engine prints, do some research, or remove your valve covers to find the intake valve at each cylinder. It’s important to know exactly where to point the plug opening, or the effort of indexing isn’t worth it.
Step 3: Install and Check Orientation
Thread the plug into the cylinder head and tighten it with light torque.
Check the mark to see which direction the ground strap faces. The goal is to align it with the intake valve.
Step 4: Use Indexing Washers
If the plug isn’t aligned in the desired position, add or swap out spark plug indexing washers until the orientation is correct.
These precision-stamped washers come in various thicknesses to help fine-tune thread engagement without over-torquing or damaging the tapered seat.
Best Practices
- Use the same plug for each cylinder: Differences in threads or depth may require different washers, even on identical engines.
- Test on the dyno: The performance gain may be modest (1–2 hp), but in a race application, that can matter.
- Monitor plug readings: Changes to plug gap, flame path, and voltage requirement can affect how the plug fires under load. These are really only concerns for highly-tuned engines, but can make a difference.
- Don’t index daily drivers: Generally speaking, it’s a lot of effort for minimal gains (unless your engine is already pushing the limit).
Let’s be clear: Spark plug indexing won’t magically turn your 400 hp street car into a 550 hp monster. But in a finely-tuned motor where every detail counts, indexing spark plugs can give you an edge.
And best of all? It’s cheap and doable. A set of spark plug indexing washers, a few extra minutes of installation time, and a little bit of patience is all it takes to unlock a more efficient burn and a more responsive engine.
If the sparkplug holes are not tapered then using index washers that are made to be crushed when torquing the plug
BUT if the hole is tapered, then user a taper type of index washer like these :
Need beforehand, a torque wrench you know is calibrated
Note :
never leave the torque wrench set to any amount of pressure as sitting unused over time will harm the compressed internal spring, so set it to zero when finished using it
Here is how to do that yourself in a few minutes