Just curious is anyone using this K&N air filter and backing plate with velocity stack on there Dyna part # 3931?

Shows a dyno increase of 6.54 Hp.

http://www.knfilters.com/search/product.aspx?Prod=RK-3931

No,
But am using K&N HD 9608 Hi-Flow filter on our '08 Fatbob.This is a direct replacement for the OEM filter without the need to change backing plate.