just to make sure the stock sprocket on the f4i is 525 16/45 right and ive researched it and if i go with the 15/47 520 it will make a huge diff right? i would also get the speedo healer and how much does that effect my gas mileage?

 

I'm 99% sure its 16/46 stock.

 

16/46 is stock size.

 

ok thanks