The real problem is heat growth. A manifold can move as temperature climbs, and if the port match goes away, the manifold or even the gasket starts hanging into the exhaust port and killing flow. Our Big Hoss Duramax race manifold is built around that issue. We control location with one bolt-size hole and one slot so the casting can grow and contract across the gasket without losing alignment. The ports are CNC-machined and intentionally overmatched horizontally, and we use truth plates on both the head and manifold so the fit is right from the start. We also built a larger multi-layer steel gasket because the stock-style gasket can intrude into the port on some heads. The result is a manifold that supports the head instead of becoming the restriction, especially in sustained wide-open-throttle use.
The video focuses on a new Banks exhaust manifold program for the Duramax platform. The manifolds are being developed for two demanding uses: Banks' Bonneville diesel streamliner and a pickup-truck application. The core engineering goal is to create a CNC-machined manifold that can expand and contract with heat without losing port alignment at the cylinder head. Rather than treating thermal growth as an unavoidable compromise, the design is built around maintaining proper alignment across the operating range.
To manage expansion, the manifold uses a locating strategy based on one bolt-size hole and one slot. That arrangement controls the manifold's position while still allowing it to grow and contract as temperatures change. Banks emphasizes that this is critical for a high-heat diesel exhaust manifold, especially in sustained wide-open-throttle use. The manifold ports are intentionally overmatched in the horizontal direction, meaning the manifold opening is wider than the head port. This prevents the manifold from intruding into the port as it moves with heat.
Banks also uses truth plates for both the manifold and the cylinder head so the port relationship can be established accurately. The intent is to ensure that the manifold slides across the gasket surface during thermal cycling without ever hanging into the port and disrupting flow.
The example shown uses an aftermarket cylinder head from Wagler. Gale explains that these heads are also being used on Banks' Top Dragster and are planned for the Bonneville streamliner as well. In that context, the manifold is not just a bolt-on part but part of a larger airflow system where preserving the head's flow capability matters. Banks' position is that a well-flowing head can be compromised by an improperly matched manifold, so the manifold must be designed not to diminish the cylinder head's performance.
That concern is especially important for the streamliner project, where the engine will operate under sustained load rather than short bursts. The current diesel land-speed record is described as 350 mph, while the Banks streamliner has already reached 382 mph. Gale notes that 400 mph is the broader target, and the manifold is being designed with that kind of continuous high-temperature operation in mind.
The manifolds are fully CNC-machined from castings, and Banks states that this may be the only CNC-ported Duramax exhaust manifold on the market. The machining process includes surfacing the ends, CNC-machining the outlet, and CNC-machining the ports. The work is done in a large CNC machine capable of handling much larger components, even something as large as a V12 engine block, though in this case it is set up for the Duramax manifold casting in raw form.
Banks is producing two different outlet sizes, both CNC-machined. The outlet plane is also precision-aligned, using the same philosophy applied to the head-to-manifold interface. That precision is intended to preserve flow and maintain consistency from the ports through the outlet.
Although the manifold is being developed for the streamliner, it is also intended for pickup-truck use. To support that dual-purpose role, the casting includes a heat-shield mounting provision for a street-driven truck application. Banks has a heat shield designed to protect the steering gear, allowing the same manifold architecture to serve both racing and street environments.
The manifold also includes instrumentation provisions on both banks. Each side has a drive-pressure, or turbine-inlet-pressure, fitting and a thermocouple fitting. That allows separate monitoring of each bank so the user can compare bank-to-bank behavior and identify issues such as injection imbalance. These provisions reflect the manifold's role as both a performance component and a diagnostic tool in a serious diesel setup.
A major issue highlighted in the video is the mismatch between the aftermarket head and the stock exhaust gasket. When the stock gasket is placed against the head, it visibly hangs into the port. Banks presents this as a clear example of how flow can be damaged even when the cylinder head itself is capable of better performance. In other words, the gasket alone can become a restriction significant enough to undermine the value of the head and manifold work.
Gale mentions that some people trim stock gaskets with snips to open them up, but that approach reduces sealing area and is not considered an acceptable solution. The problem is not merely cosmetic; it directly affects exhaust flow and therefore overall engine performance.
To address that mismatch, Banks is developing its own large-port multi-layer steel gasket. The gasket is sized to fit the actual port situation rather than forcing the port to conform to a restrictive stock opening. According to the explanation in the video, this gasket is intended to work with either stock or ported cylinder heads.
The manifold and gasket are designed as a system. With the truth plate mounted, the manifold opening can be seen to be slightly larger than the port in all directions, and especially wider in the horizontal direction. That deliberate overmatch ensures that as the manifold heats up and grows, it never protrudes into the port when cold or hot. Instead, it slides across the face of the Banks gasket while maintaining sealing and preserving flow area.
The overall engineering story is that Banks is designing the manifold for the harshest intended use first: sustained wide-open-throttle operation in the Bonneville streamliner. In that environment, thermal stability and consistent port alignment are essential. The manifold must maintain proper relationship to the head regardless of temperature, preserve the flow capability of the Wagler head, and provide accurate monitoring through pressure and thermocouple ports on both banks.
By combining CNC porting, precision outlet alignment, controlled thermal expansion, and a purpose-built multi-layer steel gasket, Banks is trying to eliminate the common exhaust-side mismatch problems that can quietly reduce performance. The result is a manifold intended to support both extreme land-speed racing and pickup-truck use without sacrificing port alignment or sealing as temperatures change.