T3 Exhaust Manifold for 12V Cummins 1989–1998 | 3-Piece Expansion Design | CARB Exempt
The Diesel Power Source® T3 exhaust manifold for 1989–1998 Dodge Ram trucks with the 5.9L 12-valve Cummins engine is a direct bolt-on replacement that flows 23% more than the factory manifold. This 3-piece expansion joint design is cast from nickel-laced ductile iron, CFD designed and flow-tested, and includes three pre-tapped ports for pyrometer and boost pressure fittings. It fits both 1st gen (1989–1993) and 2nd gen (1994–1998) 12V trucks with T3 flange turbochargers.
This manifold is CARB exempt with an Executive Order (EO) number, making it legal for use in California. It replaces OEM part number 3911349 and is one of the best first performance upgrades for any 12V Cummins work or tow truck.
Why the Stock 12V Manifold Fails
The factory 12V Cummins exhaust manifold is a single-piece casting that is prone to cracking over time due to thermal cycling. Every heat-up and cool-down cycle stresses the rigid casting, and eventually cracks develop — usually at the ends where thermal expansion is greatest. Cracked manifolds leak exhaust, reduce turbo efficiency, raise EGTs, and create an exhaust smell in the cab.
The DPS 3-piece expansion joint design solves this by allowing each section of the manifold to expand and contract independently. The expansion joints absorb thermal stress instead of transferring it to the casting, eliminating the cracking issue that plagues both factory and single-piece aftermarket manifolds.
Dedicated 12V Rectangular Port Casting
Most aftermarket manifold manufacturers cast their manifolds using a 24V round-port mold and then machine the ports to fit the 12V rectangular port head. This creates smaller, restricted port openings and poor exhaust flow transitions at the head flange.
The DPS 12V manifold uses a dedicated rectangular port mold designed specifically for the 12V head. The port geometry matches the 12V exhaust ports from the factory head to the collector, delivering unobstructed flow through the entire manifold. This is one of the primary reasons the DPS manifold outflows competitors that use adapted 24V castings.
Specifications
| Specification | Value |
|---|---|
| Design | 3-piece expansion joint |
| Material | Nickel-laced ductile iron |
| Flow Improvement | 23% more than stock |
| Turbo Flange | T3 (factory bolt-on) |
| Port Design | Dedicated rectangular port mold (12V specific) |
| Coating | Black high-temperature ceramic |
| Pyrometer Ports | 3 pre-tapped (pyro and boost pressure) |
| CARB Status | Exempt (EO numbered) |
| OEM Replacement | Replaces 3911349 |
| Fitment | 1989–1998 5.9L 12V Cummins (1st gen & 2nd gen) |
DPS 3-Piece Ductile Iron vs Stainless Steel Manifolds
| Feature | DPS 3-Piece Ductile Iron | Stainless Steel Manifolds |
|---|---|---|
| Thermal Expansion | Minimal — ductile iron expands less than stainless | Expands up to 2x more than ductile iron |
| Cracking | Expansion joints absorb thermal stress | Welds and rigid sections prone to cracking |
| Head/Gasket Stress | Low — expansion joints flex independently | High — extra expansion transfers stress to head, gaskets, and bolts |
| Leak Risk | Low — less movement at flange | Higher — more movement causes gasket sealing issues |
| Longevity | Designed for long-term thermal cycling | Can fatigue faster under repeated heat cycles |
What's Included
- DPS 3-piece T3 exhaust manifold for 12V Cummins
- Black high-temperature ceramic coating
- Standard bolts and gaskets (upgradeable to Spin Lock Bolts and Multi-Layer Gasket Kit at checkout)
Optional upgrades (available at checkout):
- Serrated Spin-Lock Bolt Kit — upgraded bolts with teeth to prevent loosening
- Multi-Layer Gasket Kit — improved sealing over standard gaskets
Note: When selecting the Spin Lock Bolt or Multi-Layer Gasket Kit upgrade, the standard bolts and gaskets are not included. The upgraded components replace them.
Key Features
- 23% More Flow Than Stock — CFD designed and flow-tested
- 3-Piece Expansion Joint Design — Eliminates cracking from thermal cycling
- Dedicated 12V Rectangular Port Mold — Not a machined 24V casting
- Nickel-Laced Ductile Iron — Handles heat without the expansion issues of stainless
- CARB Exempt (EO Numbered) — Legal for use in California
- Direct Factory Bolt-On — T3 flange matches factory manifold location
- 3 Pre-Tapped Ports — Pyrometer and boost pressure ready
- Ceramic Coated — High-temperature black ceramic finish
- Replaces OEM 3911349 — Direct replacement for factory part number
Black High-Temperature Coating
DPS exhaust manifolds are finished with a high-temperature black ceramic coating designed to handle extreme heat and real-world diesel performance conditions. This coating is rated for sustained temperatures up to 1,400°F, helping reduce surface heat, improve durability, and maintain a clean appearance under normal operating conditions. Because exhaust gas temperatures can vary significantly depending on tuning, load, and driving conditions, appearance changes may occur if those temperatures are exceeded.
Please note: The black ceramic coating is rated for temperatures up to 1,400°F. If exhaust gas temperatures exceed approximately 1,470°F, the coating may discolor and shift to a gray appearance. This is a normal result of excessive heat exposure and does not affect the performance or structural integrity of the manifold. Warranty does not cover coating discoloration or finish changes due to high EGT conditions.
Real-World Results
Customers consistently report approximately 75°F lower EGTs and turbo spool 200 RPM faster than the stock manifold. The improved exhaust flow reduces drive pressure, which means the turbo works more efficiently and the engine runs cooler under load. This manifold is one of the best first modifications for any 12V Cummins that tows or works hard.
OEM Cross-Reference
This DPS T3 exhaust manifold replaces the following OEM part number for the 5.9L 12-valve Cummins:
- Cummins 3911349
Fitment
This manifold fits 1989–1998 Dodge Ram trucks with the 5.9L 12-valve Cummins engine. Covers both 1st gen (1989–1993) and 2nd gen (1994–1998) 12V trucks with T3 flange turbochargers. Direct factory bolt-on replacement.
Fummins or Chummins swap? If you have a Ford or Chevy with a 12V Cummins swap, see the Fummins/Chummins 12V Manifold which places the turbo low and to the rear to clear the heater/AC core.
Need a T4 flange manifold? If your turbo uses a T4 flange (some aftermarket S400 setups), DPS also offers a T4 exhaust manifold for 12V applications.
Related 12V Cummins Products
Most customers see noticeably faster turbo spool, stronger midrange, and lower exhaust gas temps under load. A freer-flowing, pulse-divided manifold helps the turbo light sooner and reduces drive pressure, which improves towing and overall responsiveness.
It’s one of the best first mods for a 12-valve. You get cooler temps, better drivability, and a solid foundation for adding an upgraded turbo later.
Yes. This T3 exhaust manifold fits 1989–1993 1st gen and 1994–1998 2nd gen Dodge Ram trucks with the 5.9L 12-valve Cummins engine. It is a direct factory bolt-on replacement for the stock T3 flange manifold (OEM 3911349).
No. Unlike most competitors who machine a 24V round-port casting to fit the 12V head, this DPS manifold uses a dedicated rectangular port mold engineered specifically for the 12V exhaust port geometry. This means full-size, unobstructed port openings that match the 12V head for maximum exhaust flow.
Stainless steel expands up to 2x more than ductile iron during heat cycles. That extra expansion stresses the cylinder head, gaskets, and bolts, leading to leaks and failures over time. The DPS manifold is cast from nickel-laced ductile iron with 3-piece expansion joints, which allows natural thermal flexing without putting stress on the head or gaskets. It is designed for long-term durability under repeated thermal cycling.
Yes. This DPS exhaust manifold has been granted an exemption by the California Air Resources Board (CARB) and carries an Executive Order (EO) number. It is legal for use in California.
The DPS T3 manifold flows 23% more than the stock manifold. Customers consistently report approximately 75°F lower EGTs and turbo spool approximately 200 RPM faster. The improved exhaust flow reduces drive pressure, which makes the turbo work more efficiently and the engine run cooler under load. This is one of the best first modifications for any 12V Cummins that tows or works hard.
Yes. Standard bolts and gaskets are included. You can upgrade to the Serrated Spin-Lock Bolt Kit and Multi-Layer Gasket Kit at checkout for improved sealing and bolt retention. When selecting the upgrade, the standard hardware is replaced by the upgraded components.
15 Reviews
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Manifold for 91 12valve
It spools faster on boost an increase on boost would recommend to anyone
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Manifold
Great looking quality better looking than some of the other manifolds I’ve seen and has dual ports for temp sensors recommend it.
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DPS X 98 12V s362 turbo215 Pump
This Manifold has done what is says. Turned up 12V 362 turbo injectors and AFC mods on a 5 Speed. Lowered EGT by 75 degrees and spools at around 1550 Rpms about 200 Rpms faster than the stock Manifold. Easy to install Nice coating and welded between flanges all in a 3 piece. Sure will last for a long time. Truck runs smoother and doesn't feel laggy at all had to remove some pre boost to tone her down a bit. Thanks DPS just what I needed .
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Perfect!
sounds like new truck at 305k...mine shrank badly on ends, does make my 66mm turbo sing 2-300 rpms earlier and the top end it loud n pulls hard but also has light pedal power too
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12v Manifold
Great manifold and even better price compared to others costing more.
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On time
Shipping was sooner than expected and product is exactly as advertised
