Recommended for the Edelbrock and Batten aluminum heads. Compression ratios between 8.8 to 9.7 for 400 cubic inch big block Oldsmobiles. Compression ratios between 8.2 to 9.3 for big blocks Oldsmobile engines between 425-455. Also recommended for 469-500 cubic inch Oldsmoible engines with 8.2-9.2 to 1 compression ratios. Recommended for small block Oldsmobile engines with Edelbrock or Batten cylinder heads between 8.6-9.8 to 1 compression ratios. Recommended gap .032-.035. Projected tip. Priced per 16 plugs.