Exhaust Modifications

The role of the exhaust system is to take the spent gases away from the engine and allow for the next amount of the fuel air mixture to be drawn into the cylinders and go thru the ignition, burn, power and exhaust cycle. If the exhaust system is constricted then the burnt mixture is not all exhausted from the cylinders and hence there is less room to "get more in". Less in, equals less power and huge inefficiencies in the operation of the engine.
To remedy this issue and provide easier breathing for the engine, a larger exhaust can be fitted. Exhaust sizes up to 2.5 or 3 inches (67mm to 75 mm) will improve the flow of exhaust gases from your engine however a common mistake is to retain the existing muffler. Exhaust size increase only, will give a small increase in engine power however, combined with a free flowing muffler will deliver considerably more increase in power.
It is also better to opt for a "mandrel" bent exhaust. This means that all of the bends in the exhaust are of the same diameter as the pipe itself. Under normal circumstances exhaust pipes are bent and the pipe deforms slightly in the area of the bend, the tighter the bends the more the pipe deforms and the smaller the diameter of the pipe at the bend. This means your huge 3" exhaust is maybe 2.75" on some bends introducing restrictions to the exhaust gases, eddy currents in the gas and overall reducing the effectiveness of the exhaust system. Mandrel bent exhausts avoid this and maintain the diameter of the exhaust for the entire length of the system.