Bosch W8AC Spark Plug - Type 1 Engines (Short Reach)

The Bosch W8AC spark plug has several specifications, each indicated by numbers and letters in the product code, which helps in identifying the exact characteristics suitable for specific engine requirements. Here’s a breakdown of what each component of the model name and specifications implies:

1. W – Indicates a thread size of 14mm. This is a standard designation by Bosch where “W” specifies the diameter of the thread of the spark plug, which in this case is 14mm.

2. 8 – Heat Rating. The number after the initial letter indicates the heat rating of the spark plug. The scale typically ranges from 2 to 10, where a lower number means the plug operates hotter, and a higher number means it operates colder. A rating of 8 suggests that this spark plug is relatively colder, making it suitable for engines that run hotter or for applications requiring sustained high speeds, where additional heat dissipation is necessary.

3. A – Thread Length. This letter often indicates the reach or the length of the thread. For the Bosch W8AC, the “A” specifies that it is a short reach plug, which in this case is 12.7mm. This is important for matching the spark plug correctly with the engine`s cylinder head to avoid any potential damage or inefficiency.

4. C – Electrode Material. The last letter typically denotes the type of electrode material used. In the Bosch W8AC, the “C” stands for Copper Core Electrode. Copper core electrodes are good conductors and provide excellent heat dissipation.

Additional specifications include:

• Thread size 14mm x 1.25: This details the diameter and pitch of the thread, essential for ensuring the spark plug fits correctly into the cylinder head without cross-threading.
• 12.7mm Short reach plug: Indicates the length of the spark plug that screws into the cylinder. Short reach helps prevent the spark plug from extending too far into the combustion chamber, which could otherwise lead to piston or valve damage.
• 21mm Spanner size: Specifies the size of the tool required to install or remove the spark plug.
• M4 terminal type: Indicates the size and type of the terminal post of the spark plug, which is important for ensuring the correct fit with the spark plug wire.

This spark plug is sold individually and is designed to fit a range of air-cooled engines, from the older 25HP and 30HP up to Twinport 1600cc engines, commonly found in many classic VW models. Each of these features ensures that the spark plug can meet the thermal and fitting requirements of a variety of air-cooled engines, providing efficient performance and reliability.