The Novarossi 9901SS pipe is the defacto pipe of choice for most Novarossi engines when paired with the NV-41021 manifold this produces a good all round performance with great top and fuel mileage. The 9901SS gives a very linear feel to the power delivery making for a very easy to drive engine. Convesrley, the alternative 2096SS gives more bottom end punch making for a torquier feel to the engine.
The tuning options available with different pipes and manifolds must never be under estimated. By altering the length of the exhaust the engine will perform with notable difference. Even without changing the engine by changing pipe and / or manifold it will make a large change to the on track "feel" of the engine.
In essence a shorter manifold and pipe set up will produce higher maximum RPM but also decrease low speed torque, these are ideal for long open and flowing tracks where as a longer manifold will increase low speed torque but reduce maximum RPM. As a starting point we would ordinarily start with the medium option and move either way from there should the on track feel dictate as such. Often a longer manfold will have the effect of decreasing fuel consumption.