* Specific engine build: Compression ratio, camshaft profile, ignition system (points, electronic, HEI, aftermarket), and fuel type all influence plug heat range and material selection. A high-compression engine with an aggressive cam will require a different plug than a milder build.
* Driving style: Hard driving generates more heat than cruising, affecting plug heat range needs.
* Altitude: Higher altitudes require different heat ranges.
However, several reputable brands and heat ranges are commonly recommended for high-performance 350s in the 400hp range. You'll likely see recommendations for plugs like these:
* NGK: Often recommended are NGK TR55, TR6, or similar. The number after the TR indicates the heat range; a lower number signifies a colder plug (better for high-performance applications that run hotter).
* Autolite: Autolite's racing plugs (like the XP series) are also popular choices. Again, heat range selection is crucial, and you'd need to consult their chart based on your engine specifics.
* Champion: Champion also offers racing plugs, but similar to the others, careful heat range selection is paramount.
To find the best plug for *your* engine:
1. Consult a performance parts catalog: Summit Racing, Jegs, and similar suppliers have detailed plug selection guides that often let you filter by engine specs.
2. Check your engine's specifications: Your engine builder or a detailed build sheet should provide guidance on appropriate heat range.
3. Look at what similar builds use: Forums dedicated to 350 Chevy builds (e.g., forums on Chevrolet Performance, etc.) are a good resource to see what other people with similar setups are using.
4. Start with a recommended heat range and monitor: Once you install plugs, pay close attention to their appearance after driving. If they're excessively fouled (black/wet) they're too cold. If they're white and show signs of pre-ignition (melting), they're too hot. Adjust your heat range as needed. This is an iterative process.
Don't just pick a plug based on brand alone; the heat range is the critical factor that determines performance and longevity. Improper heat range selection can lead to engine damage. Using a properly gapped plug is also essential. Always refer to the manufacturer's recommendations for gap settings.
