The NB Circuit Spec, rebuilt entirely in titanium. Same layout as ISR's stainless system, but the full 3-piece exhaust — front and mid sections in 2.5-inch titanium with a slip-fit joint, and a titanium muffler with a 4-inch tip — is titanium end to end, which is where the weight saving and the sharper titanium exhaust note come from.

ISR hasn't tested this one on the Mazdaspeed NB, so turbo-car owners should treat fitment as unconfirmed. For a naturally aspirated NB it's the lightest way to run the Circuit Spec design. Gaskets, hardware and clamp are included.

• Fitment: 1999-2005 Mazda Miata (NB); not tested on the Mazdaspeed turbo model (per ISR)
• Full titanium construction; 3-piece design
• 2.5 in titanium front and mid sections with slip-fit joint
• Titanium muffler with 4 in tip
• Includes: titanium muffler, mid section, front section, 2x 2.5 in exhaust gaskets, 4x bolts, 4x nuts, 1x clamp