86 seven ???proper mpg???

hello I was jkust wandering what the proper amount of miles I should be getting out of a tnak of gas in a 86 rx7. I'm getting about 170 miles per full tank. I have no smoke or anything noticably wrong with the car. What could be the problem?

Thanx

Frank

the problem is usualy the guy behind the wheel,
to get better mpg, drive slower, and dont exceed 60 mph