Race and modified engines with forced induction- High compression engines with excessive boost pressure
When boost pressure exceeds the limits of what a spark plug can physically withstand, damage will occur.
Turbochargers and superchargers have been creating horsepower for a very long time. They are an effective way of boosting (hence the term “boosted”) an engines ability to create crazy amounts of additional horsepower. This horsepower can sometimes come at a cost. Those costs can range from the actual dollar amount of the components, to the consequences of too much “Go Baby Go”.
Following basic charts and guides for compression and boost will not only yield the intended outcome of your modification but also ensure you have parts left of your motor to inspect for proper tuning and set up. Many manufactures offer technical resources and recommendations for their products and have vast amounts of data and expertise at their fingertips.
The pictures in this article are from a pulling truck with a 500ci big block with a static compression ratio of 11.5:1, a supercharger creating 46 psi of boost at 8,000 RPM and running methanol fuel.
These two images show how the extremely high cylinder pressure has damaged the center electrode and forced it into the insulator. The top image shows how that force has bent the center electrode while the bottom image appears to be missing something. It is not missing anything, that is the center electrode that has been forced into the insulator.
The arrows show the distance the center electrode has been forced back into the ceramic insulator, while the circled area shows the center electrode has bent due to the extreme cylinder pressures.
Normal positioning of the center electrode within the insulator.
Within the colored circles notice the shaded areas. The top image has very little area within the terminal nut where sealing powder normally occupies that space. The bottom image, in the green colored circle area, shows the normal positioning of the center electrode. Once the excessively high cylinder pressure forced the electrode beyond its limit, no other area remained and the electrode started to bend causing the eventual failure.
Performance and modified engine applications using additional power adders such as super chargers, turbos, nitrous kits and alternate fuels, require specific spark plugs that fit the needs of those modifications as well as very precise tuning to handle the very large amounts of additional horsepower they are capable of creating. Heat range and ground electrode designs are two of the most common manipulated specifications. With the higher, more radical performance changes comes the increased likelihood of mechanical fatigue and component failure. This has increasingly become an acceptable outcome when engines are given performance modifications that exceed the structural capabilities of its components within.
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