I used the 2-disk Horstman for the can class and, later, for the Y-Pipe. I was completely inept when it came to adjustments–all I did was service it between track days. Needless to say, it eventually became unpredictable to feel when the clutch would engage, and in my ignorance I thought it was the fault of the clutch, that it worked for the can but was less effective for the Pipe.
One day the drum broke, and to me this confirmed that the Y-pipe was just too much for the 2-disk to handle (I was wrong). So I borrowed a fellow racer’s 3-disk dry clutch (a Patriot). It worked much better than my 2-disk and was more robust, so I arranged a trade (after replacing the broken drum with a new one). I’ve been satisfied since.
But I’ve since been told that the 2-disk is just fine for the Y-pipe. In fact, I’m the only one at my club who uses a 3-disk.
We have ran both the 2 disc and 3 disc in the can but have found that the 2 disc works better on larger tracks like new castle and the two are pretty even on the short tracks just due to the extra rotational mass on the 3 disc. On the Y pipe we have both as well and found that they are about even on track each have their own benefits but the 2 disc has less rotational mass which is the main reason most people run 2 disc in Yamaha. Personally we have switched to tomar 3 disc which has been a very good clutch on the Y-pipe and the can.