1994-1998 Dodge 5.9L Cummins Exhaust Parts

Exhaust System on the 1994-1998 RAM 5.9L Cummins

From the factory, the 12-valve 5.9L Cummins sends exhaust through a cast-iron manifold with a T3 turbo flange, into the Holset HX35 turbine, down a 3-inch downpipe and out a single exhaust with a muffler. There is no EGR on this engine, and no DPF or SCR to service. That keeps the layout simple: manifold, turbo flange, downpipe, muffler, tailpipe. Most of the work owners do on these trucks happens at the two ends, the manifold up front and the pipe size behind the turbo.

What fails and why

The cast manifold is the weak spot. Cast iron gets brittle after years of heating and cooling, and cracks are not unusual on these trucks, coming on faster when an engine runs hot or carries extra fuel. The signs are an exhaust tick on a cold start, soot streaks around the manifold and boost that is down from where it used to be. When the manifold comes off, the gaskets and studs come off with it, which is why gasket sets and stud kits sit next to the manifolds on this page.

Heat is the other limit. Exhaust gas temperature is what holds a 12-valve back once fueling goes up. One 300 hp 12-valve towing 6 percent grades held 1,200 F, while sustained readings above 1,250 to 1,300 F are the danger zone, with melted pistons as the extreme result. A truck on the stock turbo with no gauges is best kept at stock fueling. Flow matters too: above roughly 400 hp, the factory 3-inch downpipe becomes the restriction, and drive pressure and exhaust temperature climb as bigger turbos go on.

Stock replacement vs. upgrade

If the truck is stock and the manifold is cracked, an OEM-style cast T3 replacement with new gaskets and studs puts it back the way Dodge built it. If you have added power or tow heavy, look at parts that handle heat better. Three-piece manifolds with expansion joints suit 500 to 700 hp street trucks, and billet manifolds in T4 or T6 are the heavy-duty option, with at least one billet design backed by a lifetime no-crack warranty. Behind the turbo, a 4-inch turbo-back or downpipe-back system is the standard street upgrade, while 5-inch systems show up on compound-turbo trucks around 700 hp. For towing, an exhaust brake is the usual add-on.

What we carry

On the manifold side there is the ATS Diesel Performance Pulse Flow exhaust manifold kit for 1994-2002 5.9L trucks and an ATS 45mm wastegate adapter, plus stud and bolt kits from Fleece Performance Engineering (7mm external hex or 4mm Allen socket head), Gator Fasteners (black oxide or chrome), Mishimoto and XDP, and manifold gasket sets from Mahle and BD Diesel. BD also supplies a turbo-mount exhaust brake, a remote-mount 4-inch exhaust brake, a V-band clamp, a manual-transmission lever switch and the Torqloc torque converter control system. MBRP covers the back half with 4-inch and 5-inch 409 stainless mufflers, Armor Lite and Armor Plus mufflers, resonators, universal pipe and adapters, and tips with 4-inch to 8-inch outlets. Pacific Performance Engineering adds 3-inch and 4-inch stainless tips, and Mishimoto adds a 6-inch polished tip and an exhaust heat wrap set. To shop exhaust parts across every truck we cover, see our exhaust section.

Fitment notes

Order for the turbo that is on the truck now. The stock HX35 with its T3 flange takes a 3-inch downpipe, while an HX40-flange S300 upgrade takes a 4-inch, so a turbo-back kit has to match. Tailpipe routing changes with cab and bed: Club Cab short-bed, Regular Cab long-bed and 3500 dually systems differ, so confirm wheelbase and whether the truck has dual rear wheels. Model year 1998 is a split year. Early trucks have the 12-valve with the P7100 inline pump and a mechanical shutoff solenoid on top; later ones have the 24-valve with the VP44 rotary pump and a wiring harness. Check the engine, not just the year. Universal mufflers and tips are sized by inlet, so measure your pipe before you order, or verify by VIN with us.

Frequently asked questions

Why does my 12-valve exhaust tick when it is cold?

A tick on a cold start, especially with soot streaks near the manifold and some lost boost, is the classic sign of a cracked cast exhaust manifold on these trucks. Cast iron turns brittle with heat cycles, and cracks are not unusual at high mileage or on engines that run hot. Replace the gaskets and studs while the manifold is off.

Is a 4-inch exhaust worth it on a 1994-1998 Ram?

The factory 3-inch downpipe becomes the restriction above roughly 400 hp, which is the point where a 4-inch turbo-back or downpipe-back system pays off. That 4-inch system is the standard street upgrade for this engine. Five-inch systems are mostly seen on compound-turbo trucks making around 700 hp.

Which exhaust brake should I pick?

BD offers two styles here: the 2033135 turbo-mount brake listed for 1994-1998 Cummins and the 1037135 remote-mount 4-inch brake listed for 1989-1998 Cummins. Which one works depends on the turbo and pipe size on your truck, so check the product fitment notes against what is installed. Call us if you have changed turbos and are unsure.

How hot is too hot for exhaust temperature?

Sustained exhaust gas temperatures above about 1,250 to 1,300 F are where trouble starts, and melted pistons are the worst case. For reference, a 300 hp 12-valve towing 6 percent grades held 1,200 F. If your truck has no gauges and runs the stock turbo, leave the fueling stock.

Will these parts fit a 1998.5 truck?

Some will and some will not. A 1998 can have either the 12-valve or the 24-valve, so look for the P7100 inline pump with a shutoff solenoid before ordering. Most stud and bolt kits here are listed through 2018 or later for 5.9L and 6.7L Cummins, while the gasket sets and exhaust brakes are listed only through 1998.

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.