Relentless Automotive Development Downpipe with GESI HFC for RHO and HO Engines
High-Flow Downpipe Utilizing GESI 85200 by Relentless Automotive Development
Elevate your vehicle's performance with our High-Flow Downpipe, engineered by Relentless Automotive Development and built around the GESI 85200 4.5" high-flow catalytic converter. This system is designed not only to unlock horsepower and torque but also to improve drivability, reliability, and thermal control under demanding conditions. Constructed from premium 304 stainless steel and finished with a professional ceramic coating, our downpipe offers a combination of strength, heat management, and flow efficiency that makes it equally at home on the street or at the track. Every unit is hand-built with precision welds, heavy-duty brackets, and smooth transitions to ensure lasting performance and an OEM-plus fitment.
Designed for enthusiasts who demand more than just an exhaust upgrade, this downpipe is a complete performance solution that balances flow, durability, and thermal protection without compromise.
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Key Features
49-State EPA Designation
Utilizes the GESI 85200 4.5" high-flow catalytic converter (400 CPSI), designed to meet federal EPA guidelines in 49 states.
High Power Capability
Each GESI 85200 HFC supports 500–850 horsepower, making it suitable for high-performance builds. Trucks utilize two downpipes (one per side) for maximum flow and efficiency.
Optimized Diameter Configuration
4" tubing immediately post-turbo for maximum flow
Expands into the 4.5" catalytic converter for reduced restriction
Transitions back to 4" tubing after the cat
Smoothly tapers down to 3" tubing prior to the OEM mid-pipe connection for a direct, reliable fit
Reduced Back Pressure & Flow Gains
Larger tubing and smooth transitions allow exhaust gases to exit more freely, enhancing turbo efficiency, responsiveness, and throttle feel.
Observed Performance
During off-road event testing, this downpipe configuration showed a slight decrease in turbo spool-up time, contributing to improved response under load.
Thermal & Component Protection
Instead of traditional heat shields, each downpipe is finished with a professional-grade ceramic exterior coating. This high-performance barrier dramatically reduces radiant heat transfer in the engine bay, protecting sensitive components such as wiring, hoses, and intake piping from excessive temperatures. At the same time, the coating helps retain thermal energy inside the exhaust stream, which keeps exhaust gas velocity high for maximum flow efficiency. Beyond heat management, the ceramic layer also provides added durability, resisting surface oxidation, corrosion, and road debris impact over time.
Turbo & Wastegate Efficiency
Consistent exhaust flow improves wastegate performance, boost control, and overall turbo stability.
Durable Stainless Steel Construction
Fabricated from premium 304 stainless steel for strength, corrosion resistance, and long service life.
Custom Stainless Brackets
1/8" stainless-steel brackets are engineered to bolt into OEM mounting points, ensuring stability under extreme use—whether it’s hard launches, rough landings, or daily pothole abuse.
Integrated Flex Pipe
The 3" segment includes a flex pipe to absorb vibrations and thermal expansion, reducing stress on welds and mounting points.
Aggressive Sound
Delivers a bold exhaust tone that complements your truck’s performance while remaining refined enough for daily driving.
ECU Tune (Once Available)
To maximize the full performance potential, an ECU calibration will be required once tuning options become available.
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At Relentless Automotive Development
We engineer performance solutions with uncompromising quality. The High-Flow Downpipe with GESI 85200 offers enthusiasts the perfect balance of power, flow, and reliability.
Built to order — please allow up to 4 weeks.
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⚠️ Important Notes
Designed by an Enthusiast, for the Enthusiast
Every detail of this downpipe reflects a passion for performance and durability, ensuring it meets the expectations of those who demand more from their trucks.
An ECU tune will be required once available to fully optimize performance
Covered by a 30-day limited warranty against manufacturing defects only
Processing and Shipping Time
We kindly request a period of up to three business days for the processing and verification of product availability. In the event that the product is not in stock, a notification will be promptly sent via email.