The type and number of silencers fitted to the exhaust system will typically be dictated by law and personal preference for noise and tone. The further to the rear the silencer is fitted the less it will have an impact on the performance. A well designed silencer fitted to the rear should not reduce power by more than 3-5%. Fitted closer to the engine, where the exhaust gasses can get hot, the restriction in flow is increased thus power loss is more significant.
The most suitable types for performance are straight-through or reverse flow (also called ‘S’ flow) designs.
Straight-through types don’t have to be loud, in fact many high quality, well designed silencers are of this design. This type is the preferred for turbo engines, For naturally aspirated engines and supercharged engines, two silencers or a silencer and a resonator may be necessary to prevent exhaust ‘popping’ on over run. An open resonating chamber in the middle typically yields the quietest result for this particular reason.
Reverse flow silencers are quite different and generally do not contain any sound absorbing material. This means less weight, however poorly designed units tend to be noisy, and typically the noisy ones makes less power. The main benefit of the reverse flow design vs Straight-through is that it is less prone to popping when you lift off the throttle and coast.