EVERYBODY TALKS BAD ABOUT PRO-COMPS, THESE ARE THE PEOPLE THAT HAVE NEVER RUN THEM...I HAVE THEM ON MY 496 BIG BLOCK AND THEY WORK GREAT.... JUST AS GOOD AS ANY BIG DOLLAr DART 320 HEAD I HAVE EVER HAD.. DONT KNOCK EM IF YOU HAVE NEVER TRIED THEM... I DONT THINK PRO-COMPS WILL PERFORM LIKE A BIG BOWTIE HEAD ...OPINION GOOD LUCK....