not atal on a turbo equipped car (to a certain extent) as fuel is used to keep the combustion chambers cool, which is why turbos run alot richer than non turbos, due to the increased heat Like said tho, if its too rich youll get bore wash, and petrol sitting in the sump, which starts eating away at the bearings - not good! anywhere from low 10's to 12.0:1 on WOT for a turbo motor is fine..optimum is around 11.8 N/a is about 13.0:1 on WOT