MagnaFlow RX-8 Catalytic Converter Review (2004-2011)

If you own a Mazda RX-8, a failing RX-8 catalytic converter is not a matter of if, but when. The 1.3L Renesis rotary runs hot, burns oil by design, and cooks the stock converter's ceramic substrate until it clogs — triggering a P0420 code, hot-start problems, and a noticeable loss of power. At NLP Performance in Tampa, FL, the part RX-8 owners ask us for most is a converter that fits right, passes emissions, and lasts. This review covers the MagnaFlow California Grade Direct-Fit Catalytic Converter (part 5461150) for the 2004-2011 RX-8, plus two CARB-legal universal alternatives.

Why the Mazda RX-8 Destroys Catalytic Converters

The RX-8's catalytic converter fails because the Renesis 13B-MSP rotary engine intentionally burns oil and runs a rich, high-temperature exhaust that overheats the converter's substrate. Mazda's oil-metering system injects a small amount of engine oil into the combustion chambers to lubricate the apex seals — a normal part of Wankel operation. That oil, combined with unburned fuel from the rotary's long, trailing combustion event, sends exhaust gas temperatures and hydrocarbons through the converter that a piston engine never would.

Over 60,000-100,000 miles, that thermal load melts and clogs the honeycomb, restricting flow and choking the 1.3L twin-rotor's 232 hp. The tell-tale signs are a persistent P0420 "catalyst efficiency below threshold" code, hard hot-starts, a sulfur/rotten-egg smell, and sluggish throttle response above 5,000 rpm. Because the RX-8 was sold from 2004 to 2011 across both Series 1 (2004-2008) and Series 2 (2009-2011) cars, most surviving examples are now well past the point where the factory converter has degraded.

MagnaFlow Direct-Fit Catalytic Converter Review

The MagnaFlow 5461150 is a California Grade, CARB-compliant direct-fit converter engineered specifically for the 2004-2011 RX-8, and it is the unit we recommend for a permanent, emissions-legal repair. MagnaFlow 3D-scans the factory converter and replicates its spun-body shape, so the part bolts to the OE flanges and hangers with no cutting or welding. A single laser fusion weld on the spun body reduces leak points, the mandrel-bent stainless tubing keeps flow high, and the compact, low-mass design comes back up to operating temperature quickly for a fast light-off after a cold start.

Direct-Fit vs Universal: Which MagnaFlow Cat Fits Your RX-8?

If your RX-8 has a stock exhaust and midpipe, the direct-fit 5461150 is the right choice — it is engineered to the OE dimensions and simply bolts in. If you run an aftermarket midpipe or a custom exhaust, or you want a lower-cost CARB-legal option, MagnaFlow's California Grade universal converters let a shop weld a compliant cat into your existing pipe. All three carry MagnaFlow's California Grade CARB compliance; the difference is fit and installation labor. Prices below run roughly $1,250 to $1,900.

Installing the RX-8 Direct-Fit Converter

Installation of the direct-fit converter takes most DIYers about one to two hours with basic hand tools because there is no cutting or welding involved. The 5461150 bolts to the factory converter flanges and uses the OE hanger locations, so it drops straight into the stock exhaust path. Plan on penetrating oil for the old flange bolts, a new set of nuts and a gasket, and transferring or reusing the rear oxygen sensor. The universal converters instead require a muffler shop to cut the old cat out and weld the new body into your pipe — budget shop labor on top of the part price.

After the install, clear the stored codes and let the car complete a drive cycle so the downstream O2 sensor can confirm the new catalyst is working. If a P0420 returns immediately, check for exhaust leaks at the flanges and confirm the rear O2 sensor is healthy before blaming the converter.

Is It Legal? CARB, EO Numbers and 50-State Use

All three MagnaFlow converters here are California Grade CARB-compliant, meaning they are designed to meet or exceed California Air Resources Board requirements for legal street use in California and other states that follow CARB emissions rules. That matters because standard "federal" or EPA-only converters are not legal to install on a California-registered car, and a shop cannot pass a Smog Check or NY inspection with one. California Grade parts carry a CARB Executive Order (EO) reference so an inspector can verify compliance.

For RX-8 owners in Florida and other non-CARB states, a California Grade converter is still the safer buy: it is 50-state legal, holds up to the rotary's heat, and protects resale value if you ever move or sell the car. Always confirm the EO reference and your local emissions requirements before purchase.

Symptoms of a Failing RX-8 Catalytic Converter

A clogged RX-8 catalytic converter shows up as a P0420 code, hard hot-starts, reduced power, and often a rotten-egg smell. Because the Renesis is sensitive to exhaust back-pressure, a restricted cat robs top-end power and can make a warm engine hard to restart — a classic RX-8 flooding complaint. Watch for these signs before you are stranded:

• P0420 check-engine code — catalyst efficiency below threshold, the most common trigger.
• Hard hot-starts — a plugged cat traps heat and pressure, worsening the RX-8's known warm-restart issue.
• Power loss above 5,000 rpm — back-pressure chokes the high-revving 1.3L rotary.
• Rotten-egg (sulfur) smell — a sign the substrate is breaking down.
• Rattle from the converter — a broken-up honeycomb rattling inside the shell.