User blog comment:Na299/Ways of Gold Farming/@comment-221.127.2.68-20150524014537/@comment-24644758-20150524020841

Well I am on this event too and currently have only cash upgrade. I have no idea if it can be done without gold upgrades. But very likely I would say.

However, I would give gold upgrades when it is time, considering that  the car would be used in 2 series and the gold I earned with this method.