I think by pure luck. I have Hankook K127 now for street use very happy for the price and much better than the PZero's.
Side question: You spend a fair amount of time on a racetrack. Do you ever have issues with the differential overheating? I have a hypothesis that the Torsen is part of the issue and none of the Euro cars have one. So if you can run for an extended period of time without overheating the rear-end, that would support my claim.
I'd suggest you get in touch with Brian@BMVK except he's been MIA for at least a month.
I have never had a rear-end overheating problem. But, the club I use to get track time has drivers of many different skill levels. They break us down into groups and give us only 30 minutes of track time apiece at one time. You will get multiple times throughout the day, usually four or five, sometimes six in the summer. Might not be enough time to test your theory, but I had a 3.73 with Torsen in the 16 and the 19 has 3.55 with Torsen and neither has overheated. Of course I am in track mode which does override traction control. Don't know how much difference that would make, but maybe it does.
I don't have Torsen but I don't run very long tracks nor I run a lot of laps. A friend of mine overheated his diff on his convertable so I don't think this issue is limited to Torsen only cars.
I would think that powering out of a corner would generate more heat with a clutch or cone style diff than a Torsen. The friction surfaces are being forced to permit slip while under pressure - this being the same mechanism that makes a conventional limited slip diff gradually wear until it essentially becomes an open diff. Autocross is murder on them.
I was making the assumption that any Trac-Loc would be burnt out and essentially an open after about the first hour on track. A Trac-Loc lasts for fewer than 50 real traction 'events'. An Auburn cone diff lasts for about a 1/2 dozen.
