These stacks are for modified 1 1/4" SU or Stromberg carbs, when the outside opening is 1 3/8". The length [total height] being 3/4" base to top flange, for high rpm, 7000 rpm and higher. The dia. of the top flange is 3 1/2". You can use our sock air filters. Yes, they work to provide more air than leaving the bare carb.