ISR Performance BMW E46 Series II EP Dual-Rear Section Only - IS-S2RO-EPD-E46

The sound depends on the muffler and resonator design. A cat-back with a resonator stays closer to stock; an axle-back changes the tone more than the volume. Look for the maker's sound notes or a clip on this page.

Cat-back and axle-back systems bolt to the factory connection points. Headers and downpipes replace the factory pipe at the engine and may need new gaskets and hardware; see What's in the box.

A cat-back or axle-back needs no tune. Headers and downpipes change what the oxygen sensors see, so many cars need a tune or a sensor spacer to avoid a warning light.

Drone depends on the muffler and resonator design and your car's gearing. Systems with a resonator or an X-pipe drone less, and the maker notes when a system is built to be quiet at cruise.

An axle-back or cat-back is a jack-stands job with the right sockets and penetrating oil for rusty bolts. Headers and downpipes take more room and time, and a lift helps.

Most systems include the clamps and gaskets they need; see What's in the box. Reuse a factory gasket only if it is undamaged.

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