Track 172cup
is the ducting in the link below that i've seen a lot of people use smooth or ribbed on the inside ?
http://www.merlinmotorsport.co.uk/p....html?osCsid=f7ebc18a53c95a8beded3092e4faaaf4
http://www.merlinmotorsport.co.uk/p....html?osCsid=f7ebc18a53c95a8beded3092e4faaaf4