My brother and I are racing tomorrow and we are almost out of fuel so I went to the gas station to get some more. I usually get 87 unleaded, but I've read that it's better to get a higher octane gas, so I got 91. Well, I have a full tank in my bike right now and my brother has about a half to 3/4 full tank. My question is: at the races tomorrow, when it's time to put some gas in, is it all right to mix the 91 with my usual 87 that goes in there? Or should I just dump the gas that's in our tanks tonight? If it matters, I have a yz 250 and he has a kx 65.