Working on a 71 camaro with a built 327. It has Accel 576s plugs in it now, What plug (NGK, etc.) would go good and what heat range to start with ? Motor has aftermarket cast iron heads that have "Pro" stamped on them. Thats all we know about the motor. Thanks, John

 

Besides the plug size, which must be accurate, a lot depends on how the engine was built. Compression, cam, and RPM range will dictate the proper heat range. Learn how to read the plugs and that will give you a starting point.