Mazda 13B Rotary Swap Guide — Miata Build

A bridgeported 13B in a Miata is one of the most unique builds you can do. The combination of near-perfect weight distribution, ultra-lightweight rotating assembly, and the rotary scream at high RPM produces an experience unlike anything else on four wheels.

The 13B-REW from the FD RX-7 is the best donor engine. It comes twin-turbocharged from the factory, making 255 hp stock. The 13B-MSP (Renesis) from the RX-8 is naturally aspirated but also a popular swap core. For most Miata swaps, people go with the twin-rotor 13B-T (from FC RX-7) as a more affordable starting point.

Bridgeporting: A mild street port removes casting marks and improves flow without hurting idle quality or oil consumption. A full race port is for track-only builds. Get your porting done by an experienced rotary shop — this is not a DIY first-timer job.

Cooling is the number one concern with rotary swaps. Run a large front-mount intercooler if turbocharged, an oversized aluminum radiator, and an oil cooler. The apex seals do not forgive overheating.

Oil metering: The pre-mix system (injecting two-stroke oil into the intake) is the most reliable long-term lubrication solution for non-OEM applications. Configure your standalone ECU to control pre-mix injection correctly.

ECU: The MegaSquirt MS3Pro and Link G4X both have strong rotary support. The MS3Pro has excellent documentation for 13B builds specifically.

Realistic expectations: With proper maintenance (oil changes every 3,000 miles, no cold hard revving), a healthy 13B will easily outlast people who abuse them. Treat it well and it will reward you.