4″ GM Duramax 6.6L 2015.5-2016 Cat&DPF Delete pipe (3 bolts flange)

Here’s the detailed breakdown for the 4″ Cat & DPF Delete Pipe for 2015.5-2016 LML Duramax trucks with the 3-bolt flange connection:

Critical Fitment Verification

⚠️ 2015 Model Year Alert:

• Late 2015.5 (July-Dec) & 2016: Uses 3-bolt flange (this product)
  ▶ How to Check: Look at the turbo-to-downpipe connection:

  • band = Clamp with double bolt

  • 3-bolt = Triangular flange with 3 bolts

Technical Specifications

• Flange Type: 3-bolt triangular (OEM-style gasket included)

• Diameter: 4″ mandrel-bent

• Deletes: Catalytic converter + DPF (off-road only)

• Material: Aluminized steel (most common) or 304 stainless (premium)

• Hardware Included:

  • 3-bolt flange gasket

  • New exhaust clamps

  • OEM-style hanger brackets

Installation Requirements

1. Tools Needed:

   • 15mm socket (flange bolts)

   • Torque wrench (35-40 lb-ft for flange bolts)

   • Exhaust hanger removal tool

2. Key Steps:

   • Disconnect DPF pressure sensors (leave plugged in)

   • Reuse OEM exhaust backpressure (EBP) sensor

   • Apply anti-seize to flange bolts (prevents galling)

3. Tuning Mandatory:

   • The LML will derate within 50 miles without:

     • DPF delete tuning (via EFI Live or MM3)

     • DOC (Catalyst) monitoring disabled

Performance vs. Legal Trade-Offs

Recommended Supporting Mods

1. For Performance:

   • 5″ straight-through muffler (controls drone)

   • EGR block-off plates (prevents soot buildup)

2. For Monitoring:

   • Edge CTS3 (tracks EBP, EGT, and regen attempts)

3. For Reliability:

   • 10mm CP3 conversion (if tuning beyond +100hp)