We calculated distance with our calculator and with the help of International map agencies and distance between Gourock and Dunoon is 120 km.
If you go from Gourock to Dunoon, with normal traffic conditions and non-stop driving, you reach final destination in 1,5 hours.
Depend on car conditions and fuel quality, to travel from Gourock to Dunoon with car transport, you need 7 gallons gallons of petrol, which will cost around 10 $ with average prices.