These stacks are for the modified 1/4" carbs, with the face opening 1 3/8". The length being 2 1/2" base to top flange. The dia. of the top flange is 3 1/2" and will work best for low and medium rpm, 7000 rpm and under. You can use our sock air filters. Yes, they do look a lot sexier than the stock can filters.