1989-1993 Dodge 5.9L Cummins Exhaust Systems

Exhaust pipe on the 1989-1993 RAM 5.9L Cummins

On the first-gen 5.9L Cummins, the Holset H1C turbo bolts to the exhaust manifold at a T3 divided flange, and its outlet feeds a downpipe. From there, a single system runs under the cab to the muffler. The catalog route for these trucks is a 4 in aluminized downpipe-back system, which replaces the factory pipe and muffler only. Diesel Army's first-step upgrade list includes enlarging the exhaust pipe after the downpipe. For a rough idea of what a bigger pipe does, Banks measured backpressure dropping from 1.6 to 0.6 psi with a 4 in system on a semi-stock 1996 12-valve. That was a later P-pump truck, so treat it as a guide for a first-gen, not a promise.

Repairs and custom work

Not every job calls for a full kit. If you're repairing a section, joining pipes of different sizes or routing a custom run, universal pipe and adapters fill the gap. Stack and dual-exit setups on first-gens are custom turbo-back fabrication rather than catalog kits, and universal parts are the building blocks for that kind of work. Any time the turbo comes off for downpipe or manifold work, it makes sense to reseal it with a fresh turbo mounting gasket set.

What we carry

MBRP universal pipe and an MBRP universal exhaust adapter for joining or transitioning sections, plus the Mahle GS33582 turbocharger mounting gasket set, listed for 1991-1997 5.9L Cummins engines. For mufflers, tips and other exhaust parts, see our full exhaust section.

Fitment notes

Order 2x4 or 4x4 parts to match your drivetrain; one HX40 downpipe kit, for example, is marked for 2x4 applications only. On W250 and W350 trucks, an install video for one 4 in system warns of possible trouble at the transfer case and hanger holes that may need drilling slightly larger. The downpipe has to match the turbo: H1C/HX35-style and HX40-style outlets take different downpipes, and HX40-style 4 in downpipes are made in 2x4 and 4x4 versions for trucks that have moved to that turbo. The Mahle gasket set's listing starts at 1991, so 1989 and 1990 owners should confirm fit with the fitment checker or a call. Verify by VIN.

Frequently asked questions

What size exhaust do aftermarket kits use on a 1989-1993 Ram?

The catalog kits for these trucks are 4 in aluminized, downpipe-back systems finished with a 5 or 6 in tip. They replace the factory pipe and muffler only.

I upgraded to an HX40. Does my downpipe change?

Yes. The downpipe flange has to match the turbo, and HX40-style outlets use a different downpipe than the H1C/HX35 style. HX40-style 4 in downpipes come in 2x4 and 4x4 versions, so match yours to the drivetrain too.

Is there a stack or dual exhaust kit for a first-gen?

The stack and dual-exit setups documented on these trucks are custom turbo-back fabrication, not catalog kits. Universal pipe and adapters like the MBRP pieces here are where that work starts. Call the shop and we'll talk through what your build needs.

Not sure what fits? Call the shop at the number in the header, or use the fitment checker on any product page. We install everything we sell.