If you own a turbocharged car and want the single most effective bolt-on you can buy, it is not an intake and it is not a cat-back. It is the downpipe. The downpipe connects the turbocharger's exhaust outlet to the rest of the exhaust system, and on nearly every factory turbo car it is the tightest restriction in the whole chain. Upgrade it and the turbo spools sooner, the midrange fills in, and the engine finally breathes. The only real question is which kind: catted or catless. This guide covers the difference honestly, including the parts most articles skip.
What a Downpipe Does
Exhaust gas leaving a turbine is turbulent and under pressure. The faster it escapes, the bigger the pressure difference across the turbine, and the quicker the turbo spools. Factory downpipes choke this flow with narrow piping, sharp bends and a dense catalytic converter placed right at the turbo outlet. An aftermarket downpipe replaces that with larger diameter mandrel-bent pipe and either a high-flow catalytic converter (catted) or no converter at all (catless).
Catted Downpipes: The Street Choice
A catted downpipe keeps a catalytic converter in the system, but swaps the restrictive factory unit for a high-flow core with far less flow resistance. The result is most of the performance benefit while keeping your car legal to drive, socially tolerable and far less likely to smell of raw exhaust.
Modern high-flow cats are genuinely good. On street power levels, the difference between a quality catted downpipe and a catless one is small, often within the margin of day-to-day dyno variation. That is why our catted range covers the daily-driven platforms we know best, like the 2025+ Civic 2.0L catted downpipe, the Accord 1.5T front pipe upgrade and the Power Driven catted J-pipe for the 2022+ WRX VB.
Catless Downpipes: Maximum Flow, Maximum Caveats
A catless downpipe is a straight pipe from the turbo back. It flows the most, costs the least to manufacture, and produces the loudest, rawest sound with the most pops on overrun. On high-horsepower builds where every restriction counts, catless is the standard.
The caveats are real, though. Removing a catalytic converter is not legal for street-driven vehicles in the US, and emissions testing states will fail the car. Expect a check engine light without a tune, a strong exhaust smell, and a note that some drivers find wearing on a daily. Our position is simple: catless belongs on track and off-road builds, and street cars should run a quality catted pipe.
Power, Spool and Sound Compared
Power
Both wake up a turbo car substantially compared to stock, especially paired with a tune. Going from factory to catted is the big jump; going from catted to catless is a small increment on street power levels.
Spool
Both improve spool noticeably. Less back pressure at the turbine means boost arrives a few hundred rpm earlier, which you feel in every gear, every day.
Sound
Catted pipes deepen the exhaust note and add some induction-adjacent turbo noise. Catless pipes are markedly louder with more crackle, and on direct-injection engines can carry a distinct raw-fuel smell in traffic.
Do You Need a Tune?
Plan on it. A catless downpipe will trigger a check engine light for catalyst efficiency on virtually every modern car, which requires a tune to address. High-quality catted downpipes often run without codes on many platforms because the high-flow cat and correctly placed oxygen sensor bungs keep the ECU satisfied, but even then, a tune is what converts the added airflow into actual calibrated power. Budget for the pipe and the tune together and you will get the result you imagined.
Fitment Notes for Popular Platforms
Honda's turbo era gave the downpipe new relevance: the Civic 1.5T from 2016 on, the 2.0L turbo cars, the Accord 1.5T and 2.0T, and the K20C1-powered Civic Type R FK8 and FL5 all respond strongly, as does the FL5 Type R and DE5 Integra Type S pairing. Subaru's 2022+ WRX VB uses a J-shaped downpipe, so shop specifically for a J-pipe. Classic Honda builders running B series turbo setups will find downpipes made for ramhorn manifolds in our range. Browse the full downpipes collection for exact chassis and year listings.
Supporting Mods Worth Pairing
The downpipe opens the hot side; match it on the cold side. An upgraded intercooler keeps intake temperatures stable now that the engine moves more air, and aluminum charge pipes replace the factory plastic parts that crack under raised boost. Fresh turbo-to-downpipe gaskets and studs, available in our hardware section, make the install clean and leak-free.
Frequently Asked Questions
Is a catless downpipe illegal?
For street use in the US, yes. Federal law prohibits removing emissions equipment from road-driven vehicles, and states with inspections will fail a car with no catalytic converter. Catless pipes are for competition and off-road vehicles.
How much power does a downpipe add?
It depends on platform, boost and tune, so distrust anyone quoting a single universal number. The consistent results are earlier spool, stronger midrange and better response, with the largest gains arriving when the car is tuned to use the added flow.
Will a catted downpipe pass emissions?
A quality catted downpipe keeps a functioning catalytic converter in the system and many pass visual and sniff tests, but rules vary by state and no aftermarket pipe carries a universal guarantee. Check your local requirements before buying.
Downpipe or intake first?
Downpipe. On a turbo car the exhaust side restriction is larger than the intake side. The intake is a fine second mod, but the downpipe is the one you will feel.
The Bottom Line
For a street-driven turbo car, a high-flow catted downpipe delivers nearly all of the performance with none of the legal and livability headaches, which makes it one of the best value modifications in the aftermarket. Save catless for the track. Either way, buy quality stainless construction, pair it with a proper tune, and pick your exact fitment from the performance exhaust range.