To which part? WERA started with production, superbike, and formula classes. Somewhere around 1990-92 or so we started to allow experts to run pipes, so the expert classes went from production to superstock. Then later down the line I made the Novice production classes superstock as well as a lot of Novices were wanting to buy used Expert bikes - but no one had the stock pipes any longer. That was also around the time that the majority of street riders would put on an exhaust as well. With electronics and such the rules have developed to what they are now. So the last time I saw stock pipes racing (in any quantity) it was on Novice bikes.