The original factory specification likely called for Champion spark plugs. Modern equivalents from Champion or other reputable brands that offer similar heat ranges and construction would be suitable. You'll need to find the correct heat range. This is crucial and getting it wrong can lead to pre-ignition or fouling.
To find the best spark plug for *your* 340 Six Pack:
1. Consult your owner's manual: This is the most reliable source for the original factory recommendation.
2. Check the existing spark plugs: The plugs currently installed might provide a clue about what's been used successfully in the past. Note the heat range and brand.
3. Research heat range charts: Understanding heat range is essential. A colder plug is better for high performance and high temperatures, while a hotter plug is better for lower RPM and less aggressive driving. Too hot and you'll foul the plugs; too cold and you risk pre-ignition (detonation). Finding the right balance for your engine's setup is key.
4. Consider reputable brands: Champion, Autolite, NGK, and Bosch are all well-respected brands that make spark plugs suitable for classic muscle cars.
5. Consult with experienced Mopar mechanics or enthusiasts: They can offer valuable advice based on their experience with similar engines. Online forums dedicated to Mopars can also be a great resource.
Instead of recommending a specific plug number (which could be wrong for your engine), focus on finding the correct heat range. Once you have that information, you can easily find an equivalent from different brands. For example, a Champion plug with a specific heat range will have a NGK or Autolite equivalent. Your local parts store can help you cross-reference part numbers.
In short, don't just grab any spark plug. Research the heat range and choose a high-quality plug from a reputable manufacturer. Properly gapped plugs are also essential for optimal performance.
