I handbraked the first right turn on the autox course last Sunday with the 2.5RS, and followed through with a perfect 4-wheels-spinning drift toward the slalom. It was a little pebbly where I was coming from, though. This was with about 400 hp less than Mr. Block is using there.
I've also handbraked an STi into paved parking spaces, into my garage at a pretty good clip (180° left on gravel which transitions to concrete with about a foot on each side of the car at the garage opening), handbraked to initiate drifts on autox courses and city streets, done a few handbrake u-turns, initiating the turn with steering input plus handbrake, then following through with letting clutch out at high rpm in 1st or 2nd gear, all on paved surfaces. Handbraked it off the paved road onto our gravel path many times, too. That was a lot of fun.
Never did the handbrake turnaround on an autox course during an actual autox, though. I always just braked, downshifted to first, turned in & let the clutch out at high rpm to initiate the wheelspin, then modulated the throttle while opening the steering wheel & making very small corrections to control the drift angle. The most fun one of those was the 270° turn at the end of the runway at Sanford a couple of years ago. Mike Whitney was riding shotgun on a couple of those. I remember he enjoyed it quite a bit.
You can do some crazy shit with even a totally stock STi. It's not really that difficult once you figure it out and practice a little bit, either.
All my playing around was on STU-type tires, and I wouldn't do any of that with R compounds. I had to pull pretty hard on the lever with the cable handbrake. If I was still driving an STi around, it would probably have a hydraulic handbrake by now.
Just wanted to add that you have to know where to set the DCCD; you don't just leave it in auto mode!
