Will a 5.9 Cummins Exhaust Manifold Fit a 6.7?

Even if you’re still debating whether a 5.9 Cummins exhaust manifold will fit a 6.7, let me give you the straight answer right at the start.

Yes, a 5.9 Cummins exhaust manifold will fit a 6.7 in some instances, but it’s not a direct fitment. Some 6.7 models will allow it, while others will not. Fitment will depend on the model year, turbo mounting angle, and whether the truck still has the EGR system in place.

If you do buy or install not knowing for sure, you’re risking boost leaks, overheating, and wasted labor.

This article will explain when it fits, when it doesn’t, what needs to be modified, and what to buy if it doesn’t fit.

5.9 vs 6.7 Cummins Exhaust Manifolds — What’s the Real Difference?

Most new diesel owners assume 5.9 and 6.7 manifolds are the same because the engines look similar. They’re not.

Item	5.9 Cummins Exhaust Manifold	6.7 Cummins Exhaust Manifold
Port shape	Rectangular	Oval
Turbo flange position	Higher & angled	Lower
Flow / Backpressure	Better flow, less backpressure	Higher backpressure
EGT temps	Lower	Higher
Emissions	Not designed for heavy EGR	Designed for EGR & emissions
Durability	More resistant to cracking	Prone to cracking over time
Best use case	Performance / Towing / Tuned	Stock replacement / Emissions legal

The 5.9 manifold flows better and runs cooler. The 6.7 manifold was designed around emissions, not performance.

So why do people want to put a 5.9 manifold on a 6.7 instead of simply using a 6.7 manifold?

• Lower exhaust gas temps (EGT)
• Better boost response
• Less backpressure
• Stronger cast design = fewer cracks
• Reliability for towing & tuned trucks

So yes — the 5.9 manifold swap is popular for performance reasons, not just repair.

Will a 5.9 Manifold Fit a 6.7? (Compatibility by Year, Model, & What Needs to Be Modified)

Direct Fit or Near-Direct Fit

Engine	Model Years	Fitment	Notes
6.7 Cummins (Ram Pickup)	2007.5–2012	YES — easiest swap	Turbo flange lines up; minor line routing changes in some cases
6.7 Cummins (QSB Off-Road/Industrial)	Varies	YES / SOMETIMES	Depends on turbo flange & wastegate setup

Possible small adjustments depending on setup:

• Oil feed/drain hose length
• Wastegate line reroute
• Heat shield clearance

Not Recommended or Not Compatible

Engine	Model Years / Variant	Problem
6.7 Cummins Pickup	2013+	Oval ports mismatch, turbo flange relocation issues
6.7 HO (High Output)	Ram HD / Cab & Chassis	Support bracket and angle conflict
6.7 ISB Commercial / Medium-Duty	Multiple	Port + flange + support bracket conflict

What Happens If You “Force Install” a 5.9 Manifold on a Non-Compatible 6.7

What happens if you intentionally ignore the mismatches and force the installation?  

• Exhaust whistle and/or soot through the ports.
• Boost leak -> power loss + black smoke.
• High EGT because of poor flow.
• Rattling/broken manifold and/or turbo studs.
• Cracked manifold from uneven thermal stress.
• Short turbo life due to misaligned flange/back pressure.
• Worst case est.: leaking manifold -> constant regens -> DPF full -> turbo failure -> costly engine repairs.

If It Won’t Fit — What Are the Best Alternatives?

Replace “No” with “You should buy this instead.” That’s how users make decisions confidently.

Your Goal	Best Option	Why
Cheapest reliable fix	5.9-style 2-piece high-flow aftermarket	Most crack-resistant per dollar
Keep EGR	6.7 EGR-compatible manifold	Legal + simple
Heavy towing / hotshot	5.9 high-flow 2-piece	Fast spool & low EGT
Performance build	T4 manifold	Big turbo options
Fleet maintenance	6.7 cast upgrade manifold	Longevity, OEM-style fit

Final

Question	Answer
Will a 5.9 manifold fit a 6.7?	Yes — but only certain 6.7 years & setups
Best compatibility	2007.5–2012 pickup 6.7 Cummins
Why swap?	Better flow, lower EGT, more durable
Is forcing fit dangerous?	Yes — can damage turbo & emissions system
Best alternative for 2013+ trucks	6.7 performance manifold or T4/T6 conversion

• If your priority is reliability, towing performance, tuned power, or lower EGT, a 5.9 manifold is an upgrade — only when your 6.7 year and turbo position match.
• If your 6.7 is 2013 or newer, don’t risk the compatibility battle.
  A 6.7 performance manifold or T4 conversion gives the same benefits without the risk.

FAQs

Q1: Do I need new studs and gaskets for the swap?
Yes — always use new hardware and gaskets when installing a manifold.

Q2: Can I run emissions with a 5.9 manifold on a 6.7?
Not recommended. Port mismatch can cause regen and turbo safety issues.

Q3: Will the 5.9 manifold swap improve MPG?
Usually, yes for towing because of reduced EGT and backpressure.

Q4: Will the manifold swap void the warranty?
Yes, in most cases.

Q5: Is ceramic coating worth it?
For towing or tuned trucks — absolutely. It keeps under-hood temps lower.