Yo2001 is right. After a certain point it is useless otherwise you would see guys with 10 ft long filtercones. I use a 12 inch filtercone on my 77, 83T and 86T, It is overkill but I got them for $50 a piece and the smaller ones (9 inch) were not much less so I went with the bigger ones. Remember to keep them cleaned and oiled. Good luck. John