The factory catalytic converter is the single largest exhaust restriction on any B-Series or D-Series Honda. It chokes flow right where the engine needs to breathe freely — and on a naturally aspirated motor, every bit of backpressure costs power and throttle response.

This Flashark 2.25-inch catless downpipe replaces the factory cat section with a straight-through polished stainless steel pipe. The result: the exhaust evacuates faster, the engine revs more freely, the throttle feels more direct, and the Honda exhaust note opens up from muffled to properly aggressive — especially at high RPM where the B-Series and D-Series motors come alive.

Built from stainless steel with a polished finish. Pre-welded O2 bung included for wideband sensor use or capped with the supplied plug when not needed. Everything required for a direct bolt-on install is in the box — no welding, no cutting, no fabrication.

This is a race-inspired performance part designed for off-road and competition use only. It removes the factory catalytic converter. Check local emissions regulations before purchasing.

Key Features

2.25" (57 mm) Straight-Through Stainless Steel Piping — Full 2.25-inch inner diameter from flange to outlet. Replaces the factory cat section with unrestricted, smooth-bore tubing that flows freely across the entire RPM range, particularly above 5,000 RPM where the OEM restriction is most felt

Catless Design (Race-Off-Road) — Eliminates the factory catalytic converter — the largest exhaust restriction on the B/D-Series platform. Reduced backpressure means faster exhaust evacuation, sharper throttle response, more audible engine character, and a measurable power improvement at the top of the rev range

Pre-Welded O2 Sensor Bung — A single pre-welded O2 bung supports wideband lambda sensor installation for tuning purposes. When not in use, the included stainless plug seals the bung cleanly. No drilling, no welding required

TIG Welded Construction — All joints are TIG welded for consistent penetration and durability under repeated thermal cycling. Built to handle the heat stress of track days and aggressive street driving without cracking at the welds

Polished Stainless Steel Finish — Mirror-polished stainless resists the corrosion that destroys aluminized or mild steel pipes over time. Looks clean and professional and holds up through multiple winters without surface rust

Complete Hardware Kit Included — M10 bolts, M10 nuts, washers, donut gasket, and flange gaskets are all in the box. Nothing extra to source — bolt it on with basic hand tools

Direct Bolt-On Installation — Designed to replace the factory downpipe/cat section using OEM mounting points. No cutting, no welding, no adapter needed. Average install time is 1–2 hours

Why Go Catless?

The factory catalytic converter is the single biggest flow restriction in the Honda/Acura exhaust system. Swapping it out opens up the path for exhaust gases to exit faster — which means the engine breathes better on every stroke. The result: sharper throttle response, a louder and more aggressive exhaust tone, and a noticeable improvement in high-RPM pull. Whether you're building a street sleeper or a dedicated track car, this is one of the best bang-for-buck upgrades on a B or D-series engine.

Pro Tip: The 2.25-inch diameter is well-matched to B16, B18, and D-Series displacement. Pair this downpipe with an aftermarket intake (AEM, Skunk2, or Injen), a performance cat-back exhaust, and a proper tune (Hondata S300, KPro, or Neptune) to maximize the exhaust's benefit. On a modified B18C5 or turbo setup, step up to a 2.5" or 3" downpipe.