Undergraduate dissertation

I am writing my undergraduate dissertation on Options pricing. I am a pure maths student though. I am aiming to get 80% for my dissertation. My supervisor is not familiar with the specific topic and methods in my dissertation but he is really really impressed with how I have grasped complex topics on my own and how I worked thing out on my own. Would you get extra marks if your supervisor is not very familiar with the topic? He is very hands off and I work things out for my self. He has provided very little guidance.

Also do you have any general tips if someone was aiming for around 80%?