How much louder is a high-flow catalytic converter than the stock catalytic converter on a Mazda RX-7 FD?

A high-flow catalytic converter on an FD RX-7 is typically only slightly louder than the stock cat under normal driving conditions, but the overall volume will depend heavily on the material of the core and the rest of your exhaust setup.

Here is how the sound changes based on the configuration:

• Ceramic High-Flow Cats: A high-flow ceramic core cat will be slightly louder than stock. The most noticeable increase in volume will happen at Wide Open Throttle (WOT), though it generally isn't considered obnoxious ².
• Metallic High-Flow Cats: Metallic core cats do very little to decrease exhaust noise compared to the large, restrictive stock ceramic cat ³.

The biggest factor in controlling the volume will be your cat-back exhaust. If you pair a high-flow cat with a quality muffler (such as a Racing Beat dual exhaust), the sound level remains very manageable ². However, if you run a high-flow cat into a straight 3-inch pipe with no muffler, the exhaust will be extremely loud ².