This L5P bottom end is being reworked for jobs far beyond a stock pickup. We’re using a cast lower crankcase and cast aluminum oil pan in place of the stock sheet-metal-style lower structure to add strength where the engine needs it for military, marine, and other heavy-duty applications. The lower crankcase also includes oil return provisions with the returns deflected downward so windage doesn’t fight drainback, plus a cast-in windage tray to improve oil control. We’re also building around our own big-pin stroker crank strategy. The goal is more displacement and serious rpm without giving away crank strength, so pin-to-main overlap stays in the conversation instead of getting ignored. That means custom crankshaft, rod, and bearing development aimed at a built L5P that can take real abuse. Add the available flywheel housing options and larger 2020 oil cooler, and this engine is clearly headed toward swaps, racing, and heavy-duty installs where a stock lower end isn’t enough.
Gale Banks gives an after-hours look at a stock-based L5P Duramax long engine that Banks assembles with its own internal components. Although the engine begins as an L5P, this is specifically a Banks-built version intended as a foundation for multiple heavy-duty and performance applications. The engine shown already carries the full Denso fuel system from Duramax and has completed friction testing, pneumatic testing, and leakage testing, but it has not yet been run on the dyno.
Banks is using this long-block program as a flexible platform rather than a single-purpose crate engine. The same basic engine architecture is being prepared for military, marine, transmission-conversion, and racing uses, with Banks modifying the lower structure, oiling, crankshaft, and mounting interfaces to suit those roles.
One of the major differences from a stock L5P is the lower crankcase assembly. Banks shows both a billet version and an early experimental machined piece, explaining that this lower crankcase is intended to strengthen the block. On both sides of the structure are openings that can serve several purposes. Banks refers to them primarily as turbo oil drains, but they can also be used as oil returns for externally lubricated accessories such as an air compressor.
The oil-return passages are shaped so that the returning oil is deflected downward. That geometry is intended to keep crankcase windage from being driven into the return path and impeding flow. The lower crankcase also incorporates a full cast-in windage tray. Banks notes that some parts are not installed in the example shown because the design is still evolving, and he is preparing a patent covering features he says differ from prior designs after extensive research. He indicates that a separate video will cover those details once the patent is filed.
Banks also highlights the oil pan and lower structure materials. Both the lower crankcase and oil pan are cast aluminum, whereas the stock oil pan is sheet metal. That material change is tied directly to the heavier-duty uses Banks has in mind for the engine. The stronger lower-end structure is meant to support applications where durability, rigidity, and oil-control behavior matter more than simply retaining the stock packaging.
This reinforced lower-end approach fits the broader Banks philosophy for the L5P program: take the production engine as a starting point, then redesign the weak or limiting structural elements so the engine can survive in environments and power levels beyond its original intended use.
Banks says one of the dominant uses for this long engine is as a military engine for the Oshkosh JLTV. That application helps explain the emphasis on structural strength and robust lower-end hardware. In addition to the military version, Banks is also developing a marine version of the engine, another use case where durability, cooling, and packaging flexibility are especially important.
He also mentions a version intended to work with GM's 10L90 10-speed automatic transmission. That combination is presented as particularly attractive for swaps and performance builds because it brings modern transmission capability, including paddle-shift potential, to a high-output diesel package.
Another visible difference is at the rear of the engine. The version shown uses an SAE No. 3 flywheel housing, which allows direct mounting to an Allison transmission. Banks specifically mentions Sirius Allison compatibility as part of that configuration. This gives the engine a straightforward path into commercial, military, or other heavy-duty installations where SAE-standard interfaces are preferred.
Banks also has another housing version that uses the conventional GM transmission bolt pattern. That arrangement is intended to allow the engine to mate to GM automatic transmissions, including the 10L90/10L92 family he references. By offering both SAE and GM-pattern rear housings, Banks is building the L5P platform to serve both industrial-style installations and modern OEM-style drivetrain swaps.
Banks is especially encouraged by an updated oil-cooling package expected within a few months. He points to the 2020 oil cooler and describes it as a massive increase in cooling capacity. That improvement matters not only for new builds but also for customers installing these engines into existing vehicles.
He frames the retrofit opportunity around older trucks and pre-emissions vehicles. In that context, a Banks-built L5P paired with a 10-speed automatic becomes a modern diesel powertrain for restoration or conversion projects. Banks also notes that with the latest fuel system, the engine can achieve virtually smoke-free operation without aftertreatment, which he sees as a major advantage for diesel hot-rodding and swap applications.
Banks says the company is preparing to tear down the engine shown while another Duramax is already running in dyno cell two as part of what he calls the "Killing a Duramax" series. The purpose of that testing is to identify structural weaknesses under extreme conditions. Once those weak points are found, the engine program will receive corresponding upgrades.
This testing approach reflects the development strategy behind the Banks L5P: rather than assuming the stock architecture is sufficient, the team is deliberately pushing engines to failure so the next round of parts can address the actual limits. The long-block on display is therefore part of an ongoing engineering cycle rather than a finished, frozen specification.
Banks then points to one of the company's crankshafts and explains that Banks currently builds a big-pin billet crankshaft design along with its own connecting rods. These rods are larger than those used in Duramax engines up to the L5P, though not as large as L5P rods, because Banks wants an engine that can safely turn very high rpm. His target is well over 6,000 rpm.
He explains that Banks had developed these big-pin cranks before the L5P was even on paper. The design is a stroker crank, and Banks says the company built 7.0-liter, 427-cubic-inch engines using a 0.5 mm overbore combined with the increased stroke in this crankshaft. A key engineering concern is pin-to-main overlap. As stroke increases, the crankpin centerline moves farther from the main journal centerline, reducing the overlap between those diameters. That overlap is a major contributor to crankshaft strength. Banks says he maintained slightly better-than-stock pin-to-main overlap in these crankshafts, which he credits for their exceptional strength.
Because the desired rod-bearing size did not exist, Banks had to develop a matching bearing and connecting rod package. He describes that process as extremely difficult and says it gave him a new appreciation for why many experienced engine builders avoid creating a new rod-and-bearing size from scratch. Even so, he presents the finished result as a worthwhile solution for the rpm and strength goals of the program.
The final step he describes involves adapting these billet crankshafts to the L5P's crank-position system. On the L5P, the crank-position timing wheel is located at the rear of the crankshaft. Banks plans to machine the back side of the billet crank counterweight so that this timing wheel can be incorporated there.
That modification is part of a broader effort to turn the platform into a serious racing engine. Banks suggests it may become the first truly built L5P on the market. The overall direction is clear: start with a Duramax production foundation, reinforce the lower end, improve oil control and cooling, create stronger stroker crank and rod hardware, and then push the engine into applications ranging from military and marine service to high-rpm diesel racing.