Forza Motorsport 5

I did this with the Ferrari F12 Berlinetta that was given as the Tier 5 reward from Forza Rewards. I made a setup that you can download if you want by searching for '7000 Drift Achievement' in the tuning setup section.

Get in your Ferrari and then head over to 'Tune/Upgrade' press X to tune the car and then goto setup manager with select. You can then press select again and then search for description '7000 Drift Achievement'. Load the setup, it's free.

Once it's loaded press Y to test drive. Select Indianapolis Motor Speedway (the forth one) but before pressing A press X to turn off assists. This will help the car get sideways for longer.
Braking ABS OFF
Steering Normal
Traction & Stability Control OFF
Shifting MANUAL
Damage, Fuel & Tyre Wear OFF

Track is the oval, Brickyard Speedway.

Pause the game once it starts and go to HUD and turn Drift HUD to ON.

I was doing about 170 coming into the first left after the long straights. Stay to the right on the straight and give it a bit of handbrake to start the drift as you turn left, then steer right into the drift to keep the back end from sliding out too far and feather the throttle a little if it goes too far out.

You don't have to do 5000 all in one drift as you can see from the video I made, the two smaller drifts after the big first one added to it's total.

You can carry on round here as long as you need to, on one of your 20 perfect drifts you should get the Drifting away achievement too. I already had this from earlier drift attempts but I decided todo the rest on an empty track as the other cars were getting in the way.

The Sidewinder achievement popped after I paused and selected finish race not during the test laps.

My friend made a great guide here. It gives full detail and walk-through on how to perfectly drift. This can also get you the sidewinder achievement.

-Buy an Ariel Atom and download the tuning from misterrniceguy.
-Go to the oval on Indianapolis Motor Speedway in free play. Give yourself plenty of laps. Turn off all assists except collision. You can be manual or manual + clutch.
-Approach each turn in 5th gear.
-Drift away.

Hope this helps y'all!

If the other solutions do not help, here is what I did.

I used the Ferrari F12. I had No special tune other than the one the computer does up to A class.

I turned off abs
I turned off traction
Left the rest, kept the car automatic for shifting

On the Indy brickyard, I went to free play and had no drivatars against me.

I use the view from behind the car with slightly farther away

After turning the first two, I lined up the middle of the hood with the driving line.

Right when the driving line starts to turn yellow, I hit the a button (e brake)and pull hard left so that I was almost sideways. I held left but generally had to tap right a quick time or two to keep the car in the drift then back left. The gas is on the whole time.

As the corner runs out, you have to adjust a bit so you are straight as it doesn't count until you have control without clipping the wall.

If you have the drift meter on you can see your score, if it isn't 5000, do a quick e break and skid back and forth a little to get it above 5000 before it figures the drift was done.

If you accidentally wind up facing backwards at any point, hit the grass or wall, it won't count the drift so make sure you are adjusting to keep going forward.

If the drift counted it will say perfect drift or give you a clip recording if you successfully land a 7000 point drift.

I found where I was getting the drifts was on the corners after the long stretches using the line as a guide, as I tended to clip the wall or go on the grass for the shorter turns.

heres my take on the achievement :)