that is absolute rubbish they dont make a back box and the engine is a sleeved 150 cc engine so will not goto 185 cc and a 4 stroke 125 will not do 110 mph thats absolute garbage if you have nothing good to say DON´T you can get a 175 cc kit made up by a good piston specialist! about £200 i got quoted less but lost number! and changing sprockets a gut on www.125ccsportsbikes.com is making a full underseat exhaust with removable baffle ! check it out