Custom 3" mandrel system from header collector to tip. Worth it only for stroker or forced induction builds.
Going to 3" mandrel through the entire system is overkill on any stock or near-stock 4.0L — the engine cannot move enough air to use the additional cross-section, and you lose exhaust velocity at low RPM which can soften low-end response. The mod becomes appropriate at the 4.6/4.7 stroker level or any forced-induction setup (Sprintex, turbo) where exhaust mass flow climbs significantly.
Most builders work with a local muffler shop: long-tube header (Borla or Banks) into 3" downpipe, high-flow cat (Magnaflow 200-cell), 3" intermediate over the rear axle, Magnaflow or Dynomax 14" straight-through muffler, exit out the back. Total cost runs $500-1000 depending on shop labor and parts.
Clearance over the rear axle is the only major fitment issue. The stock tunnel and skid have room for 3" but lifted trucks with droopy axles can clatter the muffler on full droop. Some builders run the exhaust under the rear axle (poor for ground clearance) or up and over (better, requires fab).
| Part | Vendor | Est. price |
|---|---|---|
| 3" mandrel-bent kit | Summit/Jegs/Local shop | ~$350 |
| Magnaflow high-flow cat 3" | Magnaflow | ~$140 |
| Magnaflow muffler 14" | Magnaflow | ~$180 |
Written and maintained by an AZ wheeler and driveway wrencher. Always cross-reference your factory service manual — modifications affect vehicle safety and warranty. Work at your own risk.