The real question with a jailbroken Duramax L5P is not just how much fuel or tuning it will take. The limit starts with air. We want to know exactly what ambient air, the turbocharger, the intercooler, and the rest of the intake and exhaust hardware each contribute—or subtract—so we can find the point where the stock system stops helping and starts hurting the engine. The biggest concern is the stock variable-geometry turbo. It has useful compressor capacity, but the turbine side can choke as power climbs, driving exhaust backpressure hard enough to become a serious negative. The intake bridge, EGR-related castings, and other plumbing are also obvious problem areas once the truck becomes a race-only build. Our approach is to log everything with iDash DataMonster, push the stock hardware until we find the fuse, and then replace the restrictions with parts that support real airflow and keep the engine alive. That includes evaluating single-turbo replacements, intake changes, and a racing damper that can drive added charge-air or supercharger hardware. The goal is simple: minimize the parts that subtract power, maximize the parts that add it, and find the true limit of the L5P platform.
Gale Banks introduces a new Duramax L5P project at Banks Power's engine room and frames it as a full limit-finding development effort for 2019. Now that some tuners have effectively "jailbroken" the platform, the goal is to determine how far the engine can be pushed, both with its internal components and with the external hardware around it. Rather than stopping at a modest upgrade level, the plan is to identify the actual limits of the stock-based package and then develop the parts needed to support more serious power builds.
Banks says the program will rely heavily on the company's new iDash DataMonster for logging and analysis. Every performance gain and every negative side effect will be recorded so the team can separate what truly helps from what hurts. A major focus is quantifying the contribution of each stage in the air path. He wants to assign a horsepower value to ambient air, the turbocharger, and the intercooler, then compare those gains against the losses created by the piping and intake manifold system. In his view, those downstream components do not add power; they only subtract from what the boosted air system can deliver. The engineering objective is therefore to minimize those restrictions while maximizing the useful contribution from the turbocharging and charge-air-cooling system, all without sacrificing engine durability.
Banks makes clear that once an L5P is jailbroken and modified in this way, it effectively becomes a racing version of the truck. It would be intended for sanctioned racing use and would no longer be emissions-legal for normal street operation. Within that context, he identifies several obvious hardware areas that need attention when building a serious competition package.
One of the first components he calls out is the intake casting that bridges the two cylinder heads. This casting also incorporates the EGR feed, and Banks refers to it as the "sad giraffe." In a high-performance or compound-turbo application, he sees this part as a clear limitation that will need to be replaced or redesigned. He notes that Banks already produces a replacement casting for military versions of the engine, but that existing part will not fit under the hood of a pickup truck. That means a new solution will have to be developed specifically for the truck platform, especially if the engine moves to a more aggressive turbo system.
The turbocharger is another major focus. The factory unit is a variable-geometry BorgWarner turbocharger, and Banks credits its controller as a remarkable piece of hardware. He also says the compressor side has meaningful capacity. His concern is the turbine side, which he describes as entering "turbine choke" somewhere north of 500 horsepower. At that point, drive pressure rises dramatically, and he sees that as a serious negative for engine survival and overall efficiency.
Banks wants to pin down that threshold with hard data because he has heard of jailbroken L5P builds claiming more than 600 horsepower. He is skeptical about how safe that is if drive pressure is already becoming excessive. Once the team identifies the real limit of the stock turbocharger, the plan is to replace it completely. That may require designing a new mounting foot or adapting to the mounting arrangement already on the engine. From there, Banks intends to test a family of turbochargers to find the best affordable single-turbo replacement for the L5P.
Beyond the turbo itself, the exhaust side also contains race-build compromises that must be addressed. Banks points to the right-hand exhaust manifold, which includes an appendage used to route a substantial amount of exhaust gas back through the cooled EGR system and into the intake bridge. In a racing configuration with no EGR, that feature becomes unnecessary and undesirable, so the manifold arrangement will need to be changed accordingly. In other words, once the emissions hardware is removed for competition use, both the intake and exhaust architecture need to be rethought as a system rather than treated as isolated parts.
Another component Banks highlights is the vibration damper at the front of the engine. Banks has long produced viscous vibration dampers, and he references the much larger setup used on the company's military version of this engine, where the crank nose drives numerous accessories. For the L5P performance program, the company plans to create a racing-oriented damper with a bolt pattern that can support additional front-end drives.
That accessory capability is important because Banks wants the option to run a supercharger from the nose of the crankshaft or to drive a large liquid-coupled pump for a liquid-coupled charge-air-cooler system. He also notes that this damper would not be limited to race use. A street application could also benefit from the added drive capability for improved intercooling or for powering other accessories such as an air compressor. The point is not just vibration control, but creating a robust front-drive foundation for more advanced air-handling and cooling systems.
The engine is headed to Dyno 2, where Banks says the team will push it extremely hard. He is not planning to intentionally destroy the engine, but he does intend to find its fuse point. He openly admits that he does not yet know where that limit will be. His aspirational target is ambitious: somewhere in the 700 to 900 horsepower range in stock long-block form, with the possibility of approaching 1,000 horsepower if the hardware allows it. At the same time, he acknowledges the uncertainty of such testing in blunt mechanical terms-the crank could fail catastrophically or the heads could lift before those numbers are reached. The purpose of the program is to replace speculation with measured results.
Banks says some of the company's preferred tuners will be brought in to participate in the development process. He wants them to see how Banks approaches system development using the iDash setup, including turbocharger development, charge-air-cooling development, and the integration of the entire package. The broader aim is to provide new knowledge that can reshape how these high-output L5P combinations are built.
He closes by pointing to an even more ambitious concept that has interested him for years: a supercharged, twin-turbocharged L5P. Banks says that configuration is being pursued for monster trucks, and he hints that additional surprises are coming for Duramax enthusiasts as the project progresses. The overall message is that this L5P program is not just about one dyno session or one tune file; it is a structured engineering effort to map the platform's limits and develop the hardware needed to go beyond them.