This kit option increases the fuel capacity (and range) of the aircraft to a total of 30 US Gallons (2 x 15), replacing the standard 24 U.S. Gallon fuel tanks. An increase in fuel capacity from 90 Liters to 113 Liters. Choose the Viking Firewall forward kit and you will get an additional 10 Liters of usable fuel with their included header tank. The extra 33 liters is pretty close to an extra 2 hours of flight time (depending on which engine you get and how hard you run the throttle you should expect between 15 – 20 l.p.h), or 300km of range.
The price is the additional cost for a pair of larger welded aluminum wing tanks.