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Cummins ISC 8.3L Engines

Cummins 24 Valve Engine Front ViewIn the long and storied history of Cummins engine lineage, it doesn’t get more legendary than the 8.3L platform. What began as the mechanically injected 6CT 8.3L and then transformed into the electronically controlled, CAPS-fueled ISC 8.3L, was eventually followed by the high-pressure common-rail (HPCR) ISC 8.3L. No matter the injection system, the ISC 8.3L brought three decades of durability to the medium-duty segment. Used in everything from school buses to excavators (known as the QSC 8.3L in off-highway applications), and gen-sets to dump trucks to motorhomes, the 8.3L Cummins continues to enjoy a reputation for reliability, longevity, sufficient power, and easy serviceability. This time, we’re highlighting the ISC 8.3L Cummins, an engine that is much-celebrated in the motorhome segment, and one that continues to power countless RV’s down the road today.


Big Changes In ’98

Red Cummins ISC 8.3 Engine Side View

If you’re familiar with the story of how Cummins replaced the 6BT 5.9L with the ISB 5.9L, the story between the 6CT and ISC 8.3L will definitely rhyme. The 6CT to ISC changeover took place during the same period and many of the same technologies were implemented. For starters, the ISC was treated to a stiffer block with integrated fluid passages rather than utilizing external, wear-prone lines. The ISC gained a 24-valve cylinder head for improved airflow which paved the way for increased horsepower and torque. The vertically mounted injectors were also centered directly above the piston to help improve combustion and low-end torque—and the pistons they were positioned above were treated to revised bowls to further optimize combustion. And mirroring what had happened with the smaller, B-series variant, the Interact System (the IS in ISB and/or ISC) was implemented, where full-authority and fully customizable electronics were on board. Unlike the 5.9L inline mills but just like the 6CT, the ISC retained the use of mid-stop, wet cylinder liners. Then came perhaps the biggest change in Cummins 8.3L specs, the CAPS injection system…


1998-2005: CAPS

Cummins Isc 8.3 Diesel Injection Pump Side ViewJust as with any on-highway diesel engine produced around the turn of the century, the Cummins ISC 8.3L was designed to meet more stringent emissions regulations. Precise control over fuel injection events (in particular, being able to control them independently of engine speed) was a major part of meeting those standards—and the Cummins Accumulator Pump System (CAPS) allowed Cummins to do it. The CAPS system, which was patented by Cummins, is based around the use of a computer-controlled, distributor-style injection pump with individual injection lines spanning from the pump to each injector. The pump is capable of producing injection pressure as high as 1,200 bar (roughly 17,400 psi), which is sent to the injectors. The CAPS pump is supplied low-pressure fuel via a lift pump.


2003-2006: HPCR

Red Cummins Isc 8.3 24-Valve Common Rail Engine Side ViewOnce again, if you’re familiar with the ISC’s little cousin—which in this case is the ’03-’07 5.9L Cummins 24-valve common-rail engine—then you know where the story went in 2003. While engines utilizing the original CAPS system weren’t phased out completely until 2005, beginning in 2003 the Cummins ISC 8.3L was equipped with high-pressure common-rail injection. Because EPA regulations called for a 90-percent reduction in particulate matter (PM) output by 2007, Cummins (like many manufacturers) knew the most effective way to achieve it was through the use of a high-pressure common-rail (HPCR). The system could build injection pressure in excess of 29,000 psi and its quick-reacting, solenoid-activated injectors could carry out multiple injection events per combustion cycle—ideal for lowering engine noise, reducing emissions, and making more than adequate horsepower and torque.


2007-2009: HPCR, EGR, VGT, and DPF

Red Cummins ISC 8.3L Engine Front ViewAs diesel emissions tightened up even more, Cummins added a host of new technologies to the Cummins ISC 8.3 starting in 2007. High-pressure common-rail would remain, but in order to help meet the 2007 PM standard of 0.1 g/bhp-hr, a diesel particulate filter (DPF) was introduced, along with what would become a very welcomed addition to the Cummins 8.3L specs list: the variable geometry, Holset HE431VE turbocharger. A quicker-spooling turbo decreases an engine’s ability to fall “under the turbo,” where excessive PM is often produced. Regeneration cycles, whereby the exhaust gas temperature is deliberately increased in order to convert the soot in the DPF into a fine ash, were part of the DPF system’s functionality. To help curb NOx, an integrated, cooled exhaust gas recirculation (EGR) system was introduced.


2010-On: HPCR, EGR, DPF, and SCR

Red Cummins ISC 8.3L Parts
By 2010, emissions-fighting technology expanded the Cummins 8.3 specs list even further when selective catalytic reduction (SCR) was added to the ISC Cummins and, because SCR and EGR work together to decrease NOx, life was made easier on the EGR system. The SCR technology called for a NOx catalyst, a decomposition reactor, the use of diesel exhaust fluid (DEF), and a DEF dosing valve. All told, the exhaust aftertreatment system included on’10-later Cummins ISC 8.3 engines added 200 pounds of heft to the overall engine package. However, thanks to the high efficiency of its well-engineered emissions system, Cummins was still able to maintain the industry-best fuel economy. DEF usage accounted for roughly just 2-to-3 percent of fuel consumption.


Common ISC Problems And Failure Points

 ISC 8.3L Cummins Diesel Engine Parts

By 2010, emissions-fighting technology expanded the ISC 8.3L Cummins specs list even further when selective catalytic reduction (SCR) was added to the ISC Cummins. And because SCR and EGR work together to decrease NOx, life was made much easier on the EGR system’s components. The new SCR technology called for a NOx catalyst, a decomposition reactor, the use of diesel exhaust fluid (DEF), and a DEF doser valve. All told, the exhaust aftertreatment system included on ’10-later Cummins ISC 8.3L engines added 200 pounds of heft to the overall engine package. However, thanks to the high efficiency of its well-engineered emissions system, Cummins was still able to maintain industry-best fuel economy. DEF usage accounted for just 2-to-3 percent of fuel consumption.

  • Lift Pump Failure
  • CAPS Pump Failure
  • Cracked Blocks
  • Leaking EGR Cooler
  • Failed Head Gasket
  • Dropped Valves


The ISC Remanufacturing Process At Big Bear Engine Company

Red Cummins ISC 8.3L Long Block Engine on Top of a Blue Plastic

If a customer’s Cummins ISC 8.3 is unfortunate enough to suffer a serious internal engine failure but at the same time is fortunate in that many of the engine’s external components can be reused, a remanufactured ISC long block is a great solution. Coincidentally, a reman long block is about as financially feasible as replacing an ISC engine gets.

When remanufacturing an ISC 8.3L, our team of machinists and engine builders perform a full core tear down, cleaning, and inspection, and also handle all machining before the engine leaves our care. This process guarantees that each ISC 8.3L leaves the Big Bear Engine facility in perfect running condition every time.

Of crucial note in the Cummins ISC 8.3L reman process is that all of our long blocks are built with a mixture of both remanufactured and new parts. We do not recondition or refurbish old engine parts. Instead, we comprehensively rebuild your ISC back to OEM Cummins specs.


Comprehensive Cleaning

Dirty Cummins ISC 8.3 Cylinder Block
In an effort to avoid the early termination of both parts and the engine itself, we remove all impurities by stripping the block, head, rods, crankshaft and camshaft, each of which is subjected to an extensive cleaning process in a chemical jet wash or hot tank.



Cummins Isc 8.3 Crankshaft on the FloorFactory Cummins ISC 8.3 crankshafts are precision machined to exact tolerances, polished (for reduced bearing and oil resistance) and magnafluxed (to check for cracks). After that, the crankshaft is inspected by our quality control department.


Cylinder Head

Cummins Isc 8.3 Cylinder Head on Top od a White Paper MatTo both guarantee a proper mating surface with the block and achieve a finish that is compatible with the latest gasket materials, each cylinder head is resurfaced after passing initial inspection. Valve height is mic’d and the head is vacuum-tested to ensure precise valve sealing is present.



Each Cummins ISC 8.3 block is carefully inspected for cracks or other signs of damage. ToCast Iron ISC Block On the Floor eliminate distortion once the cylinder head is fastened to the block, the cylinders are bored and honed to precise tolerances. This process reduces the causes of engine blow-by considerably. All block surfaces are machined and then inspected to achieve a perfect finish.



Cummins Isc 8.3 Camshaft Close-Up ViewEach Cummins ISC 8.3 camshaft is inspected and properly machined to ensure it provides the correct lift. Lobes are also measured with a micrometer to make certain that all OEM tolerances are met.


Connecting Rods

Cummins Isc 8.3 Connecting Rods on a White BackgroundEach connecting rod is also carefully analyzed for signs of bending and/or twisting. From there, ISC rods are cleaned and then machined to OEM specifications. That process is followed by each unit being honed to its usual diameter of original equipment, which provides for even distribution of stress across the rod bearings.


New Cummins ISC 8.3 Parts

Cummins ISC 8.3 Diesel Engine Rebuild Parts Fresh pistons and rings, bearings, wet sleeves, gaskets, and seals come standard on all reman Cummins ISC 8.3 long blocks. These brand-new parts ensure dependable performance and reliability throughout the life of the engine. The new parts employed in a Big Bear long block are a combination of OEM and aftermarket components.


Further Insurance

Red Long Block Engine on Top of a Blue PlasticIn addition, wearable parts are replaced in every single engine. All Cummins ISC 8.3 core material is inspected and examined against the original specifications to certify correct dimensional tolerances. In the end, the goal of remanufacturing an engine is to restore it to a state that is as close to new as possible. Alternate parts are either new or requalified, and if new the parts are produced using the exact same manufacturing process employed on the original engine. All testing is performed according to manufacturer specs and original production standards.


ISC 8.3L Long Block Parts List:

  • Block
  • Crankshaft
  • Sleeves
  • Connecting Rods
  • Pistons and Rings
  • Cylinder Head (loaded and complete)
  • Camshaft
  • Lifters and Followers
  • All Required Upper and Lower Gaskets and Seals
  • 1-Year Warranty

Note: We can provide a new oil pump, water pump, turbo, injectors, and fuel pump for an additional cost, but these components will not come assembled to the engine.

**1-Year Warranty: First 6 Months Parts & Labor, Second 6 Months Parts Replacement Only. Ask your sales representative for a full copy of our manufactured long-block warranty.


ISC 8.3L Applications:

  • Medium Duty Trucks (ISC)
  • Motorhomes (ISC)
  • School Buses (ISC)
  • Marine Vessels (QSC)
  • Excavators (QSC)
  • Generators (QSC)
  • Heavy Equipment (QSC)


Cummins ISC 8.3L Specs

Engine Data

ConfigurationInline-six (I-6)
Displacement8.3L (506 ci)
BlockCast-iron with mid-stop (wet) cylinder liners
HeadCast-iron, 4 valves per cylinder, 6 head bolts per cylinder
Connecting RodsForged-steel
Firing Order1-5-3-6-2-4
ValvetrainSingle cam, overhead valve, roller camshaft followers
Oil Capacity6.3 gallons
AspirationFixed Geometry Turbocharger (’98-‘06), Variable Geometry Turbocharger (’07-on), charge air intercooled or aftercooled (depending on application)
Clutch Engagement Torque500 lb-ft
Injection SystemCummins Accumulator Pump System (CAPS) (’98-‘05), High-Pressure Common-Rail (HPCR) (beginning in ’03)
Emissions EquipmentEGR (’07-on), DPF (’07-on), SCR (’10-on)
Weight1,630 lbs (dry)
Horsepower240 hp to 400 hp (depending on application)
Torque670 lb-ft to 1,075 lb-ft (depending on application)
Governor SpeedHydromechanical or PSG (2,200 – 2,500 rpm)

Call Big Bear Engine Company today at 844-340-4114 for immediate sales and support for the Cummins 4BT, Cummins 6BT, 6CT, ISC, 855, QSB 4.5 L or CAT 3306. If you have any questions check out our FAQ Page. We are always ready to help or just listen to your crazy off-roading adventures!

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