What is a Downpipe? | Revv.ly Glossary

What is a Downpipe?

The downpipe is the section of exhaust directly after the turbocharger, carrying hot exhaust gases from the turbine housing to the rest of the exhaust system. It's also the single most effective bolt-on modification for turbocharged cars, often worth more power per dollar than any other part you can buy. The reason is simple: factory downpipes are restrictive, and that restriction directly limits turbo performance.
When exhaust gases exit the turbine, they're hot, fast-moving, and under pressure. Any restriction at this point creates backpressure that the turbo must work against. The turbine spins slower, boost builds slower, and the whole system operates less efficiently. Removing that restriction with an aftermarket downpipe allows the turbo to spin more freely, building boost faster and maintaining it more easily.

The Categories

Catted Downpipes -- Include a high-flow catalytic converter. These reduce emissions substantially compared to catless options while still flowing significantly better than stock. Quality catted downpipes from reputable manufacturers work well, maintain reasonable emissions, and are legal for track use in most situations. The cats are smaller and less restrictive than OEM, using higher cell density metal substrates that flow better while still converting harmful gases.
Catless Downpipes -- Remove the catalytic converter entirely. Maximum flow, maximum power potential, and legally problematic. In most jurisdictions, removing catalytic converters is illegal for street use. Some areas have strict emissions testing that catless cars cannot pass. The extra power (typically 5-15 horsepower over catted) rarely justifies the complications. Track-only cars are the appropriate application.
Stock Replacement/OEM+ -- Some manufacturers offer downpipes with slightly better flow than stock while maintaining OEM-style emissions equipment. Minimal power gains but compatible with warranty claims.

The Real-World Gains

A quality downpipe on a turbocharged car typically provides:

• 20-40 wheel horsepower on tuned applications
• Faster spool (turbo reaches target boost quicker)
• Better throttle response throughout the power band
• Often a more aggressive exhaust note
  Those numbers require a tune to realize. An untuned car with just a downpipe will show minimal gains because the ECU isn't programmed to take advantage of reduced backpressure. Downpipe + tune is the combination that delivers results.

Installation Considerations

Downpipes aren't always easy to install. Common challenges include:

• Stuck hardware -- Factory exhaust bolts seize from heat cycles. Expect to cut or break bolts.
• Turbo-to-downpipe connection -- Requires removing heat shields and often reaching into tight spaces. A V-band clamp connection (common on aftermarket turbos) is easier than factory flange connections.
• O2 sensor relocation -- Aftermarket downpipes position sensors differently. Extension harnesses may be needed.
• Clearance -- Some downpipes sit differently than stock, potentially contacting other components.
  Professional installation is worthwhile if you're not experienced with exhaust work. The cost is modest relative to the parts.

The Brands Worth Considering

Quality matters. Well-engineered downpipes use proper materials, mandrel bends for smooth flow, and quality welds. Poorly made options can crack, leak, or fit incorrectly.
Reputable options include COBB, Mishimoto, CTS Turbo, Injen, and various platform-specific specialists. The additional cost over budget options pays for better fit, finish, and longevity.
Don't forget: check emissions laws in your jurisdiction before purchasing. A catless downpipe in a strict emissions state is expensive paperweight.
Join the Revvly community to compare downpipe experiences and find what works for your platform.
Related: Boost, Tune, Headers, Intercooler
Platforms Where Downpipes Shine: VW GTI MK7, Ford Focus ST, Subaru WRX