I haven't been on a trip this long since I drove out to MI..

 

So headed to Myrtle Beach, SC and it's around 678 miles just wondering how many times will I have to fill up? 3 times?

Yes, should be between 25 and 29 mpg.  Two fills will get you there almost three should be more than enough.  

Enjoy the drive.

Thanks my first time going out to Myrtle Beach too bad I don't have much time to mess around, it's a drive out for a day and back home.

assuming you are driving a first or 2nd gen legacy 2.2, my experience is 24-26 mpg, yu can estimate 275-325 for mileage, towards 350 if your mileage is good. consider ethanol blend fuel for overall economy. 

assuming you are driving a first or 2nd gen legacy 2.2, my experience is 24-26 mpg, yu can estimate 275-325 for mileage, towards 350 if your mileage is good. consider ethanol blend fuel for overall economy. 

My car is a Ej25 I can't say for mileage since the last long trip i did I had no 5th gear

assuming you are driving a first or 2nd gen legacy 2.2, my experience is 24-26 mpg, yu can estimate 275-325 for mileage, towards 350 if your mileage is good. consider ethanol blend fuel for overall economy. 

 

I get 3mpg better with pure gas.

on the way back I pushed 340 for some reason my program I used to track my fuel is showing a avg of 31 MPG, but the picture here posted I can't complain.. I had AC on and I went a little faster going back doing around 80 with a avg around 70 mph.

 

It made a world of a difference lapping those valves that's for sure.

 

My sister gets 32 highway with her ej22 4eat legacy sedan and my ej22 5spd Outback with street tires could get 31 so that's about right. The 4eat is geared for the highway better.

lol I did not say what tires I was on but I'm still running on my snow tires the general arctics.