i just bought a 89 rx7 and i want to change the oil what kind is the best for my ride?

there should be a recommended oil type in the owners manual if you have one..if you dont, a dealership will be able to tell you the preferred type of oil, if you are stock.

I am not what part of the Country you live in or what the median temperature there would be. However, below are the recommended Oil Viscosities per Temperature for your Car:

-20 (F) to 30 (F) 5W-30
-10 (F) to 90 (F) 10W-30
-10 (F) to 130 (F) 10W-40
15 (F) to Greater Than 130 (F) 20W-50

I personally run 20W-50 all year round because I am in Florida. I have talked with a bunch of people about this topic, and 20W-50 is usually the concensus opinion. As these cars are designed to burn some amount of oil, don't use a synthetic. The car will use about a quart of oil every 3,000 to 5,000 miles. This is the case with a brand new re-built engine also. The Wankel is designed this way to keep the seals lubricated.