This achievement took me under an hour once I had worked out the score for each corner. I have uploaded my replay however it is very much trial and error. Please note these are merely estimations, you may be able to out-perform on certain corners, and slack slightly on others. For reference my exact scores after Turn 4 and Turn 7 were 6,895 and 12,488 respectively. As mentioned in the comments, you can make the hairpin in turn 8 into a separate turn and drift, however from my experience I found you scored higher by linking the two turns into one long drift. I personally scored over 3000 on Turn 8.
For this achievement used my own Kia Cee'd Drift tune, however from the comments of people with less drifting experience, "exxDudexx" has a tune for a Mazda RX7 called "mazda drift tune 500". If you get stuck on a corner and really can't score what others have scored, move on, and try to make up for the score on the next corner.Please see what scores others have achieved on each corner in the comments, as these numbers were estimated from what I achieved on each corner and are not concrete.
No traction control, no stability and no ABS. Please use normal steering. Use manual shifting and shift to 2nd at the start (by pressing B) and leave it there. When the corners become yellow pull the e-brake and let it slide itself, no gas, then feather the gas to maintain the drift. You will use lots of rewinds. After each corner has been added, turn around and get a fresh run-up for the next drift. The key to getting a high score is a combination of entry speed, the angle of the drift and length. You will want to enter with as much angle and around the 60 mph speed, making your drift last as long as possible as sideways as possible.IMPORTANT: THE DRIFT WILL ONLY COUNT BETWEEN THE CONES AND THE TYRES ON EACH CORNER.
IT IS NOT LIKE PREVIOUS FORZAS, YOU CANNOT GET SCORE ON THE STRAIGHTS.
As the corners are not massively forgiving, you will need to start on the opposite side to where the driving line suggests, sweep across and then e-brake to start the turn where the yellow starts. For a lot of corners it will naturally drift without gas, and you will only be required to maintain the drift to get the score necessary on that corner. 2nd gear should have decent power at all times and never go above 70 mph so you will always have a good entry speed.