Diamond Eye Manufacturing K4120S 4-Inch 409 Stainless Cat-Back Exhaust Kit with Turbo Direct Pipe

The Diamond Eye Manufacturing K4120S is a complete 4-inch 409 stainless steel catalytic converter-back single-outlet performance exhaust kit designed for the 2004–2005 Chevy/GMC 6.6L LLY Duramax diesel in 2500 and 3500 configurations. Fitting all cab and bed lengths, this direct-fit bolt-on system is engineered to reduce exhaust backpressure, lower exhaust gas temperatures (EGTs), and deliver a deep, aggressive diesel tone without excessive cabin drone.

This kit includes Diamond Eye's turbo direct pipe (Part #321056, CARB Exempt – Executive Order #D-778), which replaces the highly restrictive factory downpipe. The included turbo direct pipe features CNC-machined end-forms for a precise fit, mandrel-bent tubing for improved exhaust flow from the turbo outlet, and is wrapped with thermal header tape to help reduce EGTs.

Key Features:

• 4-inch diameter, 409 stainless steel construction for long-term corrosion resistance
• Catalytic converter-back single-outlet configuration
• Includes turbo direct pipe #321056 — CARB Exempt (EO# D-778)
• CNC mandrel-bent tubing for maximum flow and reduced backpressure
• Thermal heat-wrapped turbo direct pipe helps lower EGTs
• Direct-fit design utilizes OEM hanger locations for straightforward installation
• Fits all cab and bed length combinations
• Stainless steel perforated-core muffler delivers a deep tone with reduced exhaust drone
• Made in the USA
• 6-year limited warranty on stainless steel components

The K4120S is a proven upgrade for LLY Duramax owners looking to improve performance, fuel economy, and exhaust sound in a single complete bolt-on package. Manufacturer Part Number: K4120S. Included turbo direct pipe MPN: 321056.