4BT Exhaust Manifold for 3.9L Cummins | Rectangular Port (8V) | T3 Flange | 1998 and Older
The Diesel Power Source® exhaust manifold for the Cummins 4BT 3.9L engine (rectangular port, 8V, 1998 and older) is a high-flow T3 flange manifold cast from ductile iron. Designed for swap, industrial, off-road, and custom 4BT builds, this manifold improves exhaust flow and turbo spool-up over factory manifolds while providing the durability needed for sustained-load diesel applications.
The rectangular port design matches the 8V cylinder head (2 valves per cylinder) found on 1998 and older 4BT engines, which are the most commonly swapped Cummins 4-cylinder engines. The T3 turbo flange is compatible with factory turbochargers and aftermarket T3 turbos including the DPS HE351CW and S300 series.
Why Upgrade the 4BT Manifold?
Factory 4BT exhaust manifolds are designed for the engine's original industrial or commercial application, not for performance. Many stock 4BT manifolds have restrictive runner geometry, poor flow transitions, and limited turbo flange options. Upgrading to the DPS manifold improves exhaust flow to the turbocharger, which means faster spool-up, lower drive pressure, lower EGTs under load, and more usable power across the RPM range.
For 4BT builds using the DPS compound turbo system, this manifold is included with the 4BT Compound Turbo Kit (Rectangular Port). If you already have the compound kit, you do not need to purchase this manifold separately.
Specifications
| Specification | Value |
|---|---|
| Design | Single-piece |
| Material | Ductile iron |
| Turbo Flange | T3 |
| Port Type | Rectangular (8V, 2 valves per cylinder) |
| Coating | Black high-temperature ceramic (1,400°F rated) |
| Engine Fitment | Cummins 4BT 3.9L, 1998 and older |
| CARB Status | Not CARB certified |
Key Features
- Improved Exhaust Flow — Better runner geometry than factory manifolds for improved turbo spool and lower EGTs
- Ductile Iron Construction — Resists cracking and warping under thermal cycling
- T3 Turbo Flange — Compatible with factory turbochargers and aftermarket T3 turbos
- Rectangular Port — Cast specifically for 8V (2 valves per cylinder) cylinder heads
- Ceramic Coated — High-temperature black ceramic finish for heat management
- Swap and Custom Build Ready — Designed for the tight packaging requirements of 4BT conversions
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.
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.
Common 4BT Swap Applications
- Jeep Wrangler and Cherokee Swaps — The most popular 4BT swap platform
- Classic Truck Conversions — Ford, Chevy, Dodge, and International trucks
- Off-Road and Overland Builds — Broncos, Blazers, Land Cruisers, and custom rigs
- Step Vans and Commercial Vehicles — Where the 4BT was originally found
- Marine Applications — Boats using the 4BT's compact footprint
- Industrial and Stationary Power — Generators, pumps, and equipment
Fitment
This manifold fits Cummins 4BT 3.9L engines with rectangular exhaust ports (8V, 2 valves per cylinder), 1998 and older. T3 turbo flange compatible with factory and aftermarket T3 turbochargers.
Have a 1999 or newer 4BT with round ports (16V)? See the 4BT Exhaust Manifold (Round Port, 16V).
Looking for the complete compound turbo system? See the 4BT Compound Turbo Kit (Rectangular Port), which includes this manifold plus both turbos and all piping.
Related 4BT Cummins Products
Frequently Asked Questions
If your 4BT engine is 1998 or older with rectangular exhaust ports (2 valves per cylinder, 8V total), yes. This manifold uses a T3 turbo flange that is compatible with factory 4BT turbochargers and aftermarket T3 turbos. Every 4BT swap is unique, so verify your turbo flange type and clearances before ordering.
Yes. This is the same rectangular port manifold that comes with the DPS 4BT Compound Turbo Kit. If you already purchased the compound kit, you do not need to buy this manifold separately. This listing is for customers who need a manifold replacement only or are building their own turbo system.
Look at the exhaust side of your cylinder head. If the ports are rectangular (wider than tall), you have an 8V engine (1998 and older) and need this manifold. If the ports are round, you have a 16V engine (1999 and newer) and need the round port manifold.
This manifold uses a T3 turbo flange, which is compatible with factory 4BT turbochargers, the DPS HE351CW, S300 series turbos in T3 configuration, and most aftermarket T3 turbochargers commonly used on 4BT builds.
4 Reviews
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Does the job
Simple install and seems well built. Good for my project
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Solid casting
Installed on my 4BT K5 build. Manifold is thick and the flange was straight. Turbo mounted clean and the truck lights the turbo quick.
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Good manifold
Put this on a bread truck 4BT. Everything bolted up easy and the turbo placement worked great. Shipping was fast too.
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Perfect for my 4bt swap
Used this on a 4BT swapped into an old Chevy project. T3 flange lined up perfect with my turbo and the ports matched the head really well. Spool feels better than the old manifold.
