ISX15 Compound Turbo Kit: Proven Technology for Class 8
Posted by Diesel Power Source on Apr 07, 2026
ISX15 Compound Turbo Kit: Proven Technology for Class 8
Diesel Power Source® built its reputation on compound turbo systems for Cummins pickup trucks. Thousands of 5.9L and 6.7L Ram trucks are running DPS compound kits in daily towing and competition use- delivering the combination of instant low-RPM response, sustained high-load airflow, and 200 to 300 degree EGT reductions that single turbo setups simply cannot match.
That same proven compound turbo engineering is now available for the Cummins ISX15 and X15 engine in a complete Class 8 kit. The Diesel Power Source® ISX15 / X15 Compound Turbo Kit brings two-stage compound technology to one of the most widely used semi-truck diesel engines in North America — in configurations that support 550 to 700 HP while preserving Jake brake functionality and mounting in the factory position without cutting or fabrication.
Why Compound Turbos on an ISX15?
The Cummins ISX15 is a 14.9-liter engine producing anywhere from 400 to 600 HP from the factory depending on the tune. It is a strong, reliable engine but its stock turbo system- like all factory equipment- is sized conservatively for the average duty cycle, not for the conditions that push an engine hard: sustained mountain grades, heavy GCW loads, high-altitude runs, and consistent near-maximum power demands.
Owner-operators and fleet managers who push their ISX15 trucks hard know the limitations. High EGTs on mountain grades. Turbo lag on acceleration under heavy load. The constant tension between carrying speed and protecting the engine on difficult terrain. A single larger turbo addresses some of this but introduces its own tradeoff — larger turbines require more exhaust energy to spool, making them slow to respond at the RPM ranges where a loaded semi spends most of its time.
Compound turbos solve this fundamental tradeoff. The small high-pressure turbo provides immediate response at low RPM - boost arrives early, power builds cleanly from the moment the throttle opens. The large atmospheric S488 secondary turbo handles sustained high-load airflow once the engine is in its working range, providing the volume of air needed to keep EGTs controlled on long grades and demanding routes. The two turbos working in series deliver what neither can deliver alone.
From Pickup Trucks to Big Rigs: The Same Proven Technology
The engineering behind the ISX15 compound kit is not new. It is the same compound turbo design philosophy that Diesel Power Source® has developed and refined across thousands of pickup truck installations - applied and scaled to the demands of a 14.9-liter Class 8 engine.
The core principles are identical. A smaller high-pressure turbo sized for fast spool and strong low-RPM response. A larger atmospheric turbo sized for sustained high-load airflow. Inter-stage piping connecting them in series. All matched as a system rather than assembled from separately sourced components.
What changes is the scale. The ISX15 compound kit uses S400-series BorgWarner turbos with T6 flanges - substantially larger than the S300/S400 combinations used on pickup applications - sized for a 14.9-liter engine operating at commercial truck duty cycles. The high-pressure turbo uses a 1.15 A/R turbine housing for fast spool on a large engine. The atmospheric S488 uses a 1.58 A/R housing for efficient flow at the high RPM and sustained loads of a big rig application.
The result is a compound system engineered from the ground up for the ISX15 - not adapted from a smaller platform, but sized and matched for this specific engine and its operating conditions.
Two Configurations: S472/S488 and S475/S488
The kit is available in two configurations that differ only in the high-pressure turbo - the atmospheric S488 is the same in both.
The S472/S488 configuration uses a 72mm compressor wheel on the high-pressure turbo with a 1.15 A/R turbine housing. The smaller 72mm inducer spools faster and delivers boost earlier in the RPM range, making this the better configuration for trucks whose primary use is towing and pulling under load at moderate RPM. If the truck spends most of its miles in the RPM range where the engine is working under a loaded trailer - not screaming at high RPM but working steadily at road speed under weight - the S472 delivers better throttle response and bottom-end pull.
The S475/S488 configuration uses a 75mm compressor wheel on the high-pressure turbo, also with a 1.15 A/R turbine housing. The larger 75mm inducer moves more air at higher RPM, extending the power band further and supporting higher peak horsepower. It spools marginally later than the S472 but supports 600 to 700 HP for trucks with more aggressive tuning or heavier GCW requirements. For trucks targeting maximum sustained output on demanding routes, the S475 is the correct configuration.
Both configurations support Jake brake functionality - a core design requirement. Engine braking on a loaded semi is not optional, and a turbo upgrade that removes it is not a viable solution for a working truck. The ISX15 compound kit was engineered specifically to preserve factory Jake brake operation.
What Is Included
The ISX15 compound kit is a complete system. Every component needed for installation is included in one package - the same approach Diesel Power Source® takes with pickup compound kits.
The kit includes the DPS high-flow exhaust manifold in a press-fit 3-piece HSMD ductile iron design, the high-pressure S472 or S475 turbocharger with forged milled compressor wheel and 360-degree thrust bearing assembly, the atmospheric S488 turbocharger with the same bearing specification, compound mounting brackets and hardware, inter-stage piping from the high-pressure turbo outlet to the atmospheric turbo inlet, all charge air piping and silicone couplers with Kevlar and Nomex liner, V-band clamps, stainless steel braided oil feed and drain lines for both turbos, the exhaust downpipe, a high-flow air filter, and all gaskets and installation hardware.
Nothing needs to be sourced separately to complete the turbo system installation.
Fitment and ESN Verification
The ISX15 compound kit fits Cummins ISX15 and X15 engines on the CM2250 and CM2350 ECM platforms - the engine management systems used across ISX15 and X15 production from 2010 through 2024. Compatible truck platforms include Freightliner, Peterbilt, Kenworth, Volvo, International, and Western Star applications with ISX15 or X15 power.
This kit is designed for previously deleted, non-emissions trucks. Diesel Power Source® does not sell or provide emissions delete components.
Because ISX15 and X15 engines have configuration variations that can affect fitment, an Engine Serial Number (ESN) is required at the time of order. The Diesel Power Source® team verifies ESN compatibility before shipment - if your engine configuration requires any component adjustment, this process catches it before the kit arrives at the shop.
Tuning for Compound Turbos on the ISX15
As with any compound turbo system, tuning is recommended to take full advantage of the increased airflow. The compound kit delivers meaningfully better performance even on the factory calibration in most cases, but a Cummins tune calibrated for the compound configuration - adjusting fueling, boost targets, drive pressure limits, and shift strategy - maximizes the return on the investment and ensures the engine runs efficiently across its full operating range.
Monitoring boost pressure, drive pressure, and exhaust gas temperatures during initial loaded runs confirms the system is operating correctly and gives baseline data for tuning optimization. The Diesel Power Source® technical team is available for support during installation and initial commissioning.
The Class 8 Extension of a Proven Pickup Platform
For owner-operators and fleet managers who know the DPS compound kits from the pickup world, the ISX15 kit is the logical extension of that technology. The same engineering approach, the same matched-system philosophy, the same quality of BorgWarner S400-series hardware - built for a bigger engine and a harder duty cycle.
For those new to DPS compound technology, the pickup platform record speaks for itself. Thousands of working trucks and tow rigs running DPS compound systems have validated the design across millions of miles. The ISX15 kit brings that track record to Class 8.
Order the ISX15 / X15 Compound Turbo Kit - S472/S488 and S475/S488 configurations available. ESN required at checkout for compatibility verification.
See the full ISX15 and X15 performance parts lineup at dieselpowersource.com/commercial-semi/isx15.
Frequently Asked Questions: ISX15 Compound Turbo Kit
How is the ISX15 compound kit different from the S400 single turbo conversion?
The S400 single turbo conversion replaces the factory turbo with one larger S400-frame turbocharger, providing meaningfully more airflow than the stock unit but with the characteristic tradeoff of a large single - relatively slower spool at low RPM. The compound kit uses two turbos in series: a smaller high-pressure S472 or S475 that spools quickly and provides boost at low RPM, feeding into the large atmospheric S488 that handles sustained high-load airflow. The compound setup delivers both faster low-RPM response and higher peak airflow than a single turbo setup, along with cooler charge air temperatures from two-stage compression at lower individual pressure ratios.
Will the ISX15 compound kit work with my factory Jake brake?
Yes. Preserving Jake brake functionality was a core design requirement for this kit. Engine braking is essential for loaded semi-truck operation - particularly on mountain grades and extended descents - and the compound kit was engineered specifically to maintain factory engine brake operation. If you have any specific concerns about Jake brake compatibility with your truck's configuration, provide your ESN when contacting the Diesel Power Source® team and they can confirm fitment details.
How much fuel economy improvement can I expect from the ISX15 compound kit?
Fuel economy improvements vary depending on operating conditions, current tune, and driving habits, but many drivers report measurable gains from the improved combustion efficiency that cooler, denser charge air from two-stage compression provides. The most consistent fuel economy benefits are seen on loaded highway runs and on mountain routes where the compound system maintains efficient combustion at conditions that push a single-turbo truck toward its limits. Proper tuning calibrated for the compound configuration typically delivers better fuel economy results than the compound kit alone.
Does the ISX15 compound kit fit in the factory turbo position?
Yes. The kit is engineered to mount in the factory position without cutting or fabrication. This is a core design requirement - a compound kit that requires significant structural modification to install is not viable for commercial truck applications where downtime is a real cost. The kit includes all brackets, piping, and hardware needed to complete the installation in the factory turbo position on ISX15 and X15 engines across all supported truck platforms.
What is the warranty on the ISX15 compound turbo kit?
The Diesel Power Source® ISX15 compound turbo kit includes a 1-year unlimited mileage manufacturer warranty, backed by the Diesel Power Source® technical support team for fitment, installation, and tuning guidance. Contact the team directly for warranty service or technical questions.
