On chapter 7 what you want to do is kill the black bull right off the bat. He will start behind you and pass you on the left side a second or so after the race starts. When he is passing you, side swipe him. He should then fall back and pass you again on the right side this time. When he passes you, swipe him again and kill him. Then you only have to deal with blood falcon for the rest of the race.
DO NOT boost at the end of the track after you pass the pit area unless you're on the last lap (then you will be bosting like mad). You will proabably fall back to around 25th, but it's ok, you can regain it by boosting a few times past the slippery ice area and on the narrow part with no rails. If you do this you WILL finish higher than if you use up all your boost at the end of the track. Watch out for blood falcon, pico, and michael chain, they like to spin attack. If there are any mines left at the final stretch on the last lap, hit them, they will give you a boost.
Good luck! I can't beat this or chapter 9 on very hard no matter how much I try. Those are the only 2 things in the whole game that I haven't beaten.