I think that four days is enough time, but you might consider taking the fast, inland route up 1-5 from San Francisco to Medford and Grants Pass, Oregon. Then, head west to Coos Bay — that would be a day’s journey by itself, but once you got there, you could slow down and really enjoy the coastline with its many dramatic vistas, seafood restaurants and beaches. You could turtle all the way up to Astoria, if you liked, and then follow the Columbia River back to Portland. If you spent three days in that 8 hour drive, you would have time for cheap but wonderful things like hiking, picnics and leisurely beach-combing. And you won’t need a four-wheel drive car. A medium sized car or even a compact car would be fine. We have pavement!