I'm not sure where you got the 2.8 engine size because Audi does not list that engine in their information. They list 2.0, 2.7 and 3.2 liters but not 2.8. The only way(s) to know if it has a turbo is to either ask the guy or look at the engine yourself. Those cars run quite well and turbos always make them run faster. The downside to turbos is that if the previous owners were prone to mashing the throttle they may have worn out the engine prematurely. Every car can be made faster if you want to change such things as the camshaft, intake and exhaust systems and any electronic controls it might have so that part of your question will need to be asked with your budget in mind.