The BMW B58 engine has become one of the most respected turbocharged inline-six engines in the automotive world. Featured in vehicles like the BMW M240i, 340i, 440i, 540i, M340i, Z4, and the Toyota Supra, the B58 offers excellent performance, durability, and tuning potential. For enthusiasts looking to extract more power without compromising comfort or drivability, the B58 catted downpipe is one of the most impactful upgrades available.
This SEO-optimized article provides a complete overview of the benefits, performance gains, installation requirements, and tuning considerations of a B58 catted downpipe. Whether you're a car enthusiast, tuning shop, or online parts retailer, this guide helps you understand and communicate the value of this crucial performance upgrade.
What Is a B58 Catted Downpipe?
A downpipe is the exhaust component that connects the turbocharger to the rest of the exhaust system. The stock B58 downpipe includes a restrictive catalytic converter designed to meet factory emissions regulations. While effective for emissions control, it limits exhaust flow and turbo performance.
A B58 catted downpipe replaces the stock pipe with a high-flow catalytic converter—usually a 200-cell or 300-cell catalyst. This improves exhaust flow dramatically while still helping reduce emissions and maintaining a cleaner exhaust compared to catless options.
This upgrade is ideal for drivers seeking balance: power, smooth sound, and improved performance, all while avoiding the disadvantages of a fully catless system.
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Benefits of a B58 Catted Downpipe
Upgrading to a B58 catted downpipe offers powerful benefits while maintaining drivability and comfort.
1. Improved Horsepower and Torque
A high-flow catted downpipe increases exhaust flow, allowing the turbocharger to operate more efficiently. With proper tuning, you can gain:
15–35 horsepower
20–50 lb-ft of torque
Faster spool
Stronger mid-range pull
While not as aggressive as a catless setup, the difference is still impressive for a daily-driven vehicle.
2. Deeper and Cleaner Exhaust Sound
The B58 catted downpipe provides a deeper tone without excessive volume or rasp. Expect:
Richer exhaust tone
Subtle burbles with tuning
Minimal drone
More refined cold starts
You get a sporty sound without attracting unwanted attention.
3. Reduced Smell and Improved Emissions
Unlike catless downpipes, a catted downpipe keeps exhaust odor and raw fumes to a minimum. This makes the car more pleasant to drive daily and more environmentally friendly.
4. Fewer Check Engine Light Issues
Because a catalytic converter is still present, the B58 catted downpipe is far less likely to trigger catalyst-efficiency codes. Although a tune is still recommended, the system is more stable and easier to manage compared to catless options.
Do You Need a Tune with a B58 Catted Downpipe?
While some high-flow catted designs may function on stock tuning, a Stage 2 tune is highly recommended. Tuning ensures:
Safe and optimized air-fuel ratios
Maximum horsepower and torque gains
Smooth boost control
Prevention of CEL (check engine light)
Enhanced exhaust pops and burbles
Pairing tuning with your B58 catted downpipe unlocks the full potential of the upgrade.
Choosing the Right B58 Catted Downpipe
To get the best performance and reliability, ensure your downpipe includes:
304 or 316 stainless steel construction
TIG-welded joints for strength
Mandrel-bent tubing for smooth airflow
Heat shielding or ceramic coating
High-quality catalytic cores such as HJS 200-cell units
These features ensure longevity, fitment, and optimal exhaust flow.
Installation Guide & Tips
Installing a B58 catted downpipe takes about 1–2 hours for an experienced technician. Tips include:
Make sure all turbo flange bolts are tightened evenly
Use new gaskets for a proper seal
Check for exhaust leaks during and after installation
Consider combining with a midpipe for improved tone
Ensure adequate heat protection around sensitive engine components
Proper installation ensures maximum performance and reliability.
Cost of a B58 Catted Downpipe in 2025
Pricing typically ranges from:
$450–$900 for standard high-flow catted downpipes
$900–$1,500 for premium options with HJS catalytic converters
$120–$250 for professional installation
While more expensive than catless versions, the added comfort, better emissions, and cleaner sound make it a worthwhile investment.
Final Verdict: Is a B58 Catted Downpipe Worth It?
Absolutely. For drivers who use their car daily but still want strong performance gains, improved turbo response, and a deeper, cleaner exhaust note, the B58 catted downpipe is the ideal upgrade. It strikes the perfect balance between power, sound, and practicality, making it one of the most popular modifications for the B58 engine platform.
