Recommended for the Edelbrock and Batten aluminum heads. Nitrous Oxide or Turbo charged with compression ratios greater than 15.5 Unlimited rpm. Stroker Nitrous or Turbo small blocks between 390-440. Also recommended for Nitrous Oxide or Turbo big blocks up to 507 with a compression ratios that exceed 15.5. Recommended gap .028 to .032. Priced per 16 plugs.