Spark Plug
Sooo – which spark plug to get, that’s one of the big questions.
After having installed new tuning parts, it's time for some fine-tuning. Once the mechanical parts are all lined up, the usual questions come up:
- Is my carburetor adjusted properly?
- Is the heat range of the spark plug appropriate for my engine set-up?
- What is the right torque for the spark plug?
- How to read the spark plug?
Well, let's take a look at the spark plug. By looking closely at the spark plug, we can tell if the combustion in the cylinder is working the way it should. When needing to change the spark plug, you're bound to have some questions.
Tight, Tighter, Off
HOW TIGHT TO TIGHTEN SPARK PLUGS?
Basically, you can determine the tightening torque of the spark plugs in 2 ways:
- This is probably the easiest and safest method to install the spark plug with the appropriate torque. Simply look at the first table below, find your spark plug type, check the appropriate torque and set your torque wrench to the right value.
- The tightening torque is determined via the angle: Let's assume you want to install a spark plug with a flat seat and a diameter of 12 mm. Then you’d get the correct torque if you tighten the spark plug with half a turn (180°).
How to read a spark plug
By looking at the spark plug you can see if your mixture is too rich or too lean, or if you are using a spark plug with the wrong heat rating.
- A black electrode usually indicates a mixture that is too rich.
- A brownish / greyish electrode indicates that the mixture is correct.
- A rather light or white electrode indicates that the mixture is too lean.
Attention!!! Your engine may be damaged when using the wrong heat value.
Breakdown of Spark Plug Codes
So you have a spark plug, but the codes don’t mean anything to you? No problem! We’ll try to shed some light on this complicated subject.
Based on the diagram below you can determine your spark plugs so you can easily switch between different manufacturers if needed or wanted.
For this purpose, we created a table for you, where you can find the matching counterpart by other manufacturers. For example:
- NGK vs Bosch
- Bosch vs Denso
- NGK vs Denso
You will find the list here
What is the heat range of a spark plug?
A "hot" spark plug dissipates little heat - this is achieved by special heat insulation materials or simply a larger quantity of said insulation material. A "cold" spark plug is exactly the opposite, a lot more heat is conducted out of the tip. You probably guessed why installing a colder spark plug is on the to-do list for many engine tuning measures. As soon as you change something in the engine that increases performance, the result is almost without exception a higher combustion temperature which in turn means that we move away from the ideal temperature range of the original spark plug which can then cause ignition problems. A colder spark plug counteracts this.
With Bosch, Champion and BERU and many other manufacturers, a lower heat rating means a colder spark plug. NGK and Denso do it the other way around, a lower heat rating indicates a hotter plug.
Here is a little chart:
How to adjust my carburetor based on spark plug reading?
Well, that’s a pretty extensive topic, so we did a separate how-to, which you can find here:
Notes:
- Unfortunately, there is still no uniform standardization among spark plug manufacturers for the heat value code system. Bosch, for example, identifies an increasing heat range with increasing numbering. With Champion and NGK, the heat range decreases as the number increases.
- When using interference suppressed spark plugs, we recommend not to use a spark plug cap that is also interference suppressed. Since the 2 resistances installed in both parts add up, interference suppression resistance will ultimately be too high.
- When changing the spark plugs, always check your manual first. It usually tells you the correct spark plug.