The only place turbos are not allowed are "sanctioned" grudge races, which aren't really grudge races, but heads up class racing since there is no real aspect of grudge racing other than no times and the hypothetical "run what ya brung and hope ya brung enough" mentality. The biggest difference is that the sanctioned races are heads up and most grudge races aren't, due the mismatch of the bikes / riders. Big 8 or similar races are really quick 8, no bar races that are usually limited to bikes that have never shown their times (or now fairly often just eliminating turbos all together). If it is a real grudge race, they are allowed, but good even luck getting race unless you hustle for awhile and then finally get one, that you win...it will likely be the last race you get.