Here's Why The Cummins 12-Valve Is One Of The Greatest Truck Engines Of All Time
No diesel engine on earth is as legendary as a 12-valve Cummins. Not only is the inline-six known for its awesome stock torque figures, but the 1,100 pound iron hulk from Columbus, Indiana has a reputation for being almost literally unkillable, even after it’s been modified to produce prodigious power figures. The “five nine” is a tough sunovabitch. Perhaps the toughest of all sunovabitches
Today, in the fourth installment of “Engines You Should Know,” I’m breaking out some heavy weaponry to convince you once and for all that inline-sixes are simply the best engines of all.
If somehow the modern all-aluminum 4200 Vortec Atlas engine from General Motors didn’t convince you, I guess I can understand. If the supremely mod-able 2JZ-GTE in the Toyota Supra still didn’t have you nodding your head, then perhaps you need to see a doctor. And if after those two, the bulletproof Ford 300 inline-six wasn’t enough for you to see the light, well, I have the antidote to your ailment: the legendary Cummins 12-valve, the engine that served as the backbone of the now-bustling diesel performance community.
To help tell the tale of the “five nine,” I reached out to Cummins’ marketing director David Goggins, who told me that the engine’s durability is rooted in its design for grueling industrial applications, saying:
A lot of the reason that engine is as durable as it is is because we designed it to be a heavy duty, commercial kind of engine.
He went on to say that the 5.9-liter engine actually originally started as a joint venture between the Indiana-based diesel engine company and Case Corporation, which builds tractors and construction equipment.
And indeed, starting in 1984 (well before the 5.9-liter engine ever found itself powering a Dodge Ram), Cummins offered three different variants of the 5.9-liter called the 6B, 6BT (turbocharged) and 6BTA (turbocharged, aftercooled), which served duty in tractors, combines, excavators, road graders, pavement rollers, boats, field sprayers and even school buses.
These are all seriously heavy duty applications. Add that to the fact that these engines were available in dozens of different markets with different climates and work environments (like Russia, China and India), and you can imagine how relatively understressed that Cummins Turbodiesel was once it finally made its way into a Ram pickup in 1989.
When Dodge put the Cummins Turbodiesel into its Ram in 1989, a legend was born. GM and Ford couldn’t compete with their relatively gutless diesel offerings; the Cummins blew them out of the water. Even though the Cummins 12-valve only cranked out 160 horsepower, with its long-stroke and undersquare design (4.02-inch bore, 4.72-inch stroke), the engine made 400 lb-ft of pavement-destroying grunt. Chevy’s 6.2-liter and Ford’s 7.3, by comparison, weren’t even making 250 and 350 lb-ft, respectively.
But perhaps even more impressive than its factory torque numbers is the engine’s reputation for longevity. Once you start looking at the mechanical bits, you begin to see just how overbuilt the B-Series engine really is. The block and head are cast iron, the crankshaft and connecting rods are forged, the seven main bearings are massive, and like many heavy-duty diesel trucks, the crank and cam are connected by a steel timing gear—not a chain or belt like you’d find in normal cars and trucks. The Holset turbos are also know to last until the end of time.
There’s really not a lot going on with this engine; simplicity, really, is what makes the silky-smooth inline six unkillable. The cam is in the block, actuating pushrods to open and close two valves per cylinder, the geroter-style oil pump is right up front on the accessory drive, there’s no aftertreatment system (just a muffler), and the fuel injection system is purely mechanical.
I talked with Tyler from Diesel Power Products, a Washington-based Diesel performance parts supplier, and he told me the basic formula for why the Cummins 12-valve is such a beast, saying it’s just “too dumb to die.” And that mechanical fuel injection system, he says, is the key to what truly makes the 12-valve “dumb” (but in a good way).
Unlike the later 24-valve ISB model that came around in mid-1998—which used a Bosch VP44 electronic rotary style pump—the 12-valve offered between 1989 and 1998 used a fully mechanical fuel injection system that used the cam to time when fuel was injected into the cylinders.
This, Tyler told me, made the engine “The most reliable, simplest, as basic-as-it gets, fully-mechanical diesel engine” a diesel tuner could ever ask for; in fact, the vehicle literally only needed a couple wires to turn the motor over with a starter; and once it was running, the engine needed no electronics at all. Compare that to the bag of snakes all modern engines have under hood, and you realize just how simple this motor is.
Perhaps even more interesting than reliability and simplicity, Tyler says, is that the fully mechanical fuel system gave the end user “complete control” of how the engine generates its power.
The Cummins 12-valve is hilariously simple and reliable, but what puts it over the top as the greatest diesel pickup truck motor of all time is how easily it can be modified to produce hilarious power numbers. Tyler told me “there’s no other platform like it in the diesel industry as far as control.” And a lot of that control comes from what’s known as the coveted “P-Pump.”
Early diesel Rams (’89 to ’91) came with a mechanical VE rotary fuel injection pump that really wasn’t so great for tuning. But from 1994 to 1998, Cummins threw on the Bosch Bosch P7100 mechanical injection pump, also known as the “P-Pump”—a part that changed the diesel tuning world forever.
The P-Pump opened up a whole new array of tuning options; Tyler says the P-pump is so versatile, it allows owners to add power with almost no effort whatsoever, saying:
It’s pretty much the only platform in a truck where you can literally not spend a dime and gain 70 horsepower without opening your toolbox.
The P-Pump, as Tyler puts it, is “basically a little engine in itself.” Driven by the engine’s cam gear, the P-Pump is an injection pump that gets fed fuel from the lift pump (which takes fuel from the tank). The injection pump’s six plungers—which ride on a camshaft in the pump housing—move up and down in barrels. That upward movement pressurizes the fuel and pushes it through the delivery valve, which meters the fuel and sends it into the engine’s cylinders through an injector.
The way the P-Pump is set up allows for lots of easy modifications. Among those mods are fuel plates with different “cuts” to reduce the restriction of fuel flow at high engine speeds.
Between installing a new fuel plate (or just hacking up the old one with a grinder), replacing the governor spring with a stiffer one (usually owners go with a 3k to 4k spring) for better throttle response, and tuning the preboost screw (for better low rpm fueling) and starwheel (for improved throttle response), basic adjustments to the P-Pump can add 150 horsepower to a Cummins 5.9. This, of course, assumes that the injectors, lift pump and turbo have been adjusted accordingly.
Tyler puts it simply: “You can turn up the little engine to turn up your big engine.”
There’s even more Cummins 12-valve owners can do to add power besides fiddling with the P-Pump. With a different intake and exhaust, bigger turbos, a better lift pump, bigger injectors, perhaps a beefier crankshaft damper, new valve springs and pushrods, some basic head tweaks, and maybe a girdle at the base of the block to prevent crank wrap, many of the stock internals can handle 1,000 horsepower without issue.
It’s A Legend
While Ford and GM have swapped out their diesels a number of times since 1989, architecturally, the Dodge’s Cummins has remained fairly similar to the original.
Still, the Cummins 5.9 saw a number of little throughout the years. A few years after its introduction in mid 1991, the engine added an intercooler. Then in 1994, the motor changed from a rotary Bosch VE rotary pump to the P-Pump.
The 12-valve went away in 1998, replaced by a 24 valve which offered better breathing. At the same time they made the swap to 24 valves, Cummins put in Bosch VP44 electronic fuel injection; though the injection pump was still driven by the cam, the timing of fuel injection was no longer mechanical, instead driven by a solenoid.
In 2003, the Ram’s 5.9-liter switched to a Bosch common rail system. The big change happened in 2007. For the beginning part of the model year, the 5.9-liter stuck around. But starting in January of 2007, the 5.9 was finally replaced by a bored and stroked version with 6.7-liters of displacement. The change brought a fairly complex after treatment system with it to meet emissions, which warranted the increase in displacement to maintain performance.
Many diehards decry the complex emissions components and the electronic fuel injection system, as they both do a number on tune-ability. Regardless, the 6.7-liter Cummins, and frankly any truck with a big chrome “C” on the fender, gets tons of respect from diehard diesel enthusiasts around the world.
But undeniably, of all Cummins pickup truck engines, the 12-valve 5.9-liter is the king. Cooper from Diesel Power Products says “It’s probably the most reliable platform ever made on any diesel truck.”
It wasn’t perfect, as many 12-valves were plagued with the “Killer Dowel Pin,” (seen in the picture above) which could back out and get squeezed between the cam gear and the gear cover, ultimately destroying the engine. But that’s a fairly straightfoward fix, and if you look at the nearly 10,000 people who are part of the Cummins High Mileage Club, and the dozens of 5.9-liter owners who have crested 1 million miles, you realize why this motor is regarded by many as the very best diesel engine ever put into a pickup.
11 Reasons Why the 12-Valve Cummins Is the Ultimate Diesel Engine
A simple design with unmatched reliability, tremendous performance potential and rugged, million-mile durability sums up the appeal of the 12-valve 5.9L 6BT Cummins. The 12-valve 5.9L 6BT Cummins came out of the box with 230hp, 440 lb-ft of torque and a P7100 inline injection pump. While it began life as an agricultural engine, its popularity picked up immensely once it was put into Ram trucks starting in 1989.
To thousands of diesel lovers, this 1,100-pound hunk of iron is the patriarch of the modern diesel performance era. The ¾-ton and 1-ton Dodge Rams they grace can be made to produce 500 rwhp with relative ease, rack up more than 20 mpg on the highway and easily last more than a half a million miles. In addition to being the power plant of choice in the truck pulling game, the 12-valve is a regular choice in the engine swap world as well, powering countless Jeep, rat rod, muscle car and dragster projects.
But exactly why is a 20-year-old diesel — straddled with ancient injection technology — so high on everyone’s priority list? Scroll along as we pinpoint all of its strong suits. From free horsepower to a near-indestructible design, to the immense parts interchangeability that exists across all model years (including on-road, off-highway and marine applications), the following 11 reasons spell out why the 12-valve version of the 5.9L is so legendary.
1. Simple Design
Meet the 12-valve version of the 5.9L Cummins, produced from ’89-'98. A cast-iron block and head, forged-steel crankshaft and connecting rods, an inline-six design and mechanically controlled direct injection all play into the hands of a power plant built for maximum reliability and longevity. A stroke of 4.72 inches (accompanied by a 4.02-inch bore) yields 359 cubic inches, incredible low-rpm torque and remarkable fuel efficiency.
Along with it being in an inline engine’s nature to produce gobs of torque, they’re also easier to work on than the V8 competition. You can pull the turbo in minutes and a novice mechanic can replace the water pump in well under an hour. The one drawback is that with very few performance modifications, the 12-valve is known to wreak havoc on transmissions and axles. So while added power comes easy, the rest of the powertrain often requires reinforcement in order to cope with what the 5.9L can dish out.
2. Stout Connecting Rods
The forged-steel connecting rods found in the 12-valve 5.9L (and ’98.5-’02 24-valve engines) are of an I-beam design and capable of easily handling 800 rwhp in stock form. For drag race and sled pull applications, a host of aftermarket companies offer polished, shot-peened and balanced versions of the factory rod, which can be made to withstand 1,200 rwhp (give or take) before bending.
3. Heavy-Duty Rod Bolts
Even though the factory rods can handle north of 800 rwhp, the stock rod bolts are on borrowed time past this point as they can back out with age and increased engine speeds. Luckily, ARP manufactures heavy-duty rod bolts for the ’89-’02 5.9L, which offer approximately 23 percent more tensile strength than the factory units (PN 247-6303).
4. 6 Bolts Per Cylinder
With six 12-mm diameter head bolts per cylinder, the 5.9L Cummins is rarely ever at risk of blowing a head gasket, even with serious boost and cylinder pressure in the equation. In fact, the stock head bolts can stand up to as much as 100 psi of boost before stretching! For this reason, a lot of 5.9L gurus simply re-torque the factory hardware (vs. adding head studs) before pushing big boost.
In this photo, the owner of a ’94 Dodge Ram re-tightened the head bolts (from the center out) to 150 ft-lb at the same time he added a compound turbo arrangement. His fuel and air mods would eventually subject the stock head bolts to 80 psi of boost — and the head never lifted.
5. P7100 (The Holy Grail)
While the 12-valve was produced from ’89-’98, most folks seek out the ’94-’98 version. These engines were equipped with the mechanical Bosch P7100 injection pump (also known as “P-pump” or inline pump), which features six plunger and barrel assemblies, a cam and delivery valves. When the camshaft rotates (the cam is in charge of the firing order), its lobes move the six plungers up and down in their respective barrels (thereby creating injection pressure).
As you can imagine, there is a lot of room for improvement with so many moving parts inside the P7100. Larger diameter plungers and barrels, bigger delivery valves, quick-rate cams, different rack plugs and performance fuel plates are all available.
In addition, advancing the timing of the P7100 improves performance considerably. Most factory P-pumps were set at a conservative 12.5 degrees (BTDC), but bumping up into the 18-19-degree range is always good for a noticeable boost in power, and is also considered about as far as a daily driven setup should be taken (before cold start and drivability issues surface). In competition sled pull engines, it’s not unheard of for pumps to be set at 40+ degrees of timing.
6. Free Horsepower
Being a mechanically-injected engine, you’re not beholden to electronically interfacing with the ECM when you make fueling changes on the 12-valve Cummins. This means you can add horsepower with a few simple hand tools and your own two hands. The free mods begin with the AFC (air fuel control) housing shown below, which sits at the rear (top) of the aforementioned P7100 injection pump.
Moving the AFC housing all the way forward (toward the front of the truck), turning the star wheel beneath the AFC housing toward the passenger side of the engine, removing the fuel plate and disabling the turbocharger’s wastegate are all methods of adding horsepower. In fact, performing all of the above often results in a 100-hp gain, if not more.
7. Interchangeable Parts
While not everything is interchangeable between the ’89-’93 5.9L and the ’94-’98 versions, a host of parts can be swapped over. Among the list of interchangeable hard parts includes the camshafts, connecting rods, the turbos are similar and a P7100 injection pump can be added to the ’89-’93 engines (in place of the fuel-limited rotary VE pump) with the right components and know-how. Adding a P7100 to the first generation 12-valve engine effectively takes the truck’s horsepower capability from 350 rwhp to 600 rwhp. For those kinds of gains it’s definitely worth the hassle of hunting down all the conversion parts you need.
8. Affordable Injector Upgrades
Unlike today’s electronically controlled, common-rail diesel injectors that can run upwards of $3,000 per set, performance injectors for a 12-valve typically range from $450 to $1,000 (give or take). One common injector comes from the 370-hp version of the 12-valve used in marine applications. Made by Bosch, the marine 370 injectors feature a 5-hole nozzle with 0.012-inch diameter orifices (known as 5x12’s in Cummins-speak), can add up to 100 hp and retail in the $450 to $500 range.
A set of Stage 4 units from Dynomite Diesel Performance (shown above) will run you just over $1,000, but due to their 5x0.014-inch nozzles can support more than 800 rwhp with the right amount of airflow. The largest streetable injector we come across are the popular 5x0.018-inch nozzle units. Without a doubt, mechanical injectors are where it’s at for making budget-friendly horsepower.
9. HX35: One Tough Customer
The Holset HX35 found on ’94-’98 12-valve engines is one of the toughest factory turbochargers we’ve ever come across. Even though it was designed to see 20 psi of boost in the 5.9L Cummins’ application, it doesn’t seem to be out of its efficiency range at double the boost. While making 35 to 40 psi (courtesy of a disabled wastegate), the HX35 not only yields more power, but lower exhaust gas temperature (EGT) as well. And with a larger (14cm) or modified (ported) factory 12cm exhaust housing, exhaust flow increases, drive pressure drops and the HX35 can support 450 rwhp — not bad considering these engines start out with 160 to 215 hp at the crank, depending on the model.
10. High-Flow Heads
Despite all the progress that’s been made with the 24-valve head design over the years (a 24-valve head has been used on the Cummins line since ’98.5), competitive sled pullers and drag racers seeking the most horsepower possible almost always revert back to the 12-valve cylinder head. In fact, it’s not uncommon to find a 12-valve head sitting atop a 6.7L Cummins’ block in the upper echelon of diesel motorsports. With the intake shelf milled off, the intake and exhaust ports opened up and multi-angle valve jobs with huge valves added, the 12-valve unit can’t be topped in the flow department. But while a worked over factory 12-valve head can flow extremely well, due to the way they were cast, there is only so much material you can remove before you compromise the structural integrity of the head (they often crack after limited use).
Looking to get more flow and reliability out of a competition 12-valve head, Hamilton Cams had completely new cylinder heads cast (pictured above), designed specifically to incorporate more meat around the ports (especially on the exhaust side). More material means more porting (material removed) is possible without sacrificing durability (cracking). Hamilton’s top-of-the-line Warhead cam can be made to flow a whopping 310 to 340 cfm per cylinder (vs. 150 cfm on a stock 12-valve head), and in dyno testing has shown gains of as much as 300 hp on 2,500 to 3,000 hp Super Stock class sled pull engines.
11. Endless Performance Potential
With maxed out 12-mm, 13-mm, even 14-mm P-pumps, 5x18, 5x25 or larger injectors, and today’s highly advanced aftermarket turbochargers, the sky is the limit on what a 12-valve can do in a competition environment. This ’93 Dodge W250, owned by Cole and Cory Dow, is one of the best examples of everything a 12-valve is capable of. The truck was a competitive sled puller, ran 9s in the quarter-mile (yes, 9s!) and even did a little street driving — to the tune of more than 18 mpg.
Their ’93 model year Cummins is graced with the coveted 215-hp variant of the P7100, a cam out of a ’94 engine, an S475 BorgWarner turbo, a water-to-air intercooler and a custom header the Dow’s fabricated themselves. At the dragstrip, nitrous is added to the equation, which culminates in 1,100-rwhp and 9-second blasts through the 1320. The old Dodge gets its power to the ground via a J&H Performance-built 47RE four-speed automatic and a Sun Coast manual valve body. Don’t believe a 6,000-pound, 25-year-old Dodge can run 9s? Check out this 9.87-second run, and then back it up by watching this 9.64-second pass at 139 mph!
Cummins Engine Information
To ensure proper runability the ECM and PCM must year match. If there is a mis-match you will encounter runability and other issues.
The 1999½ - 2002 24-Valve engines are computer controlled and provide a bit more horsepower than the earlier engines. For this engine we provide wiring instructions to help you make it run in your Ford or Chevy. The Dodge PCM is required if you want to use OBDII diagnostics or an aftermarket tuner that requires the data link connector. Without the Dodge PCM,diagnostic information can still be accessed at a Cummins dealer through the Cummins data link connector located in the engine wiring harness, but certain performance programmers will not work as a result.
Be prepared to use the Auto trans style Cummins ECM when adapting the 24 valve Cummins to an automatic transmission. Apparently there is a difference in how the ECM adjusts fueling depending on the idle load. When a standard trans style ECM is used with an Auto trans the engine may lope (run rough) at idle. This issue seems to be even more evident when high performance upgrades are added.
The 2001-2002 engines require an electronic speed signal input to run properly. Ford trucks that have a rear axle speed sensor can easily accommodate this, and it can be done in an older truck with an aftermarket speed sensor. It’s just another thing you need to know.
Be aware that some of these engines have what is referred to as a "53 block." This number is cast onto the side of the block just above the oil pan rail on the rear driver’s side or front passenger side. These blocks are known to crack on the exterior water jacket.
The thermostat housing on these trucks also points toward the driver’s side of the truck, so if you plan to run a Ford radiator that has the upper hose connection on the passenger side of the radiator, you will want to buy our straight up thermostat housing to make your upper radiator hose connection easier.
0 - 3200
Max Stock Torque- 555-650 lb-ft
See our Common Rail Conversion Information article for more detailed information.
Cummins Common Rail 2003-2009, 5.9L/6.7L - Generation 3
The Cummins common rail engines are a great choice for your conversion. They offer great power and reliability. Engine tuning upgrades can be done electronically with several tuning service businesses existing in the US and Canada. Full engine diagnostic capabilities are also retained.
There are differences in the various model years you’ll want to be aware of before sourcing an engine. If you are unsure if your ECM is from an automatic or manual transmission truck we can verify this if you provide us with the ESN listed on the ECM. Below are some conversion related notes for your consideration.
2003-2004 with Manual Trans ECM:
- Original APPS (accelerator pedal position sensor) mounted under battery.
- ECM is compatible with DCS’s harness modification service and pedal module.
- Key recognition security system was optional on some models which may require a re-flash of the ECM.
2003-2004 with Automatic Trans ECM:
- Original APPS (accelerator pedal position sensor) mounted on engine. Tihs is retained. Pedal kit is required to operate the engine mounted APPS.
- ECM is compatible with DCS harness modification service.
- Key recognition security system was optional on some models which may require a re-flash of the ECM.
- Must designate automatic trans engine is used if using DCS harness modification service. There are differences compared to the manual trans engine.
- Both the Automatic and Manual trans are compatible, however the Manual trans ECM has been reported to be more desirable for power & tuning.
- Key recognition security system was optional on some models which may require a re-flash of the ECM.
2006-2009 5.9 & 6.7 Liter:
- Dodge TIPM (Totally Integrated Power Module) required for OBD port communication (On Board Diagnostics).
- ECM re-flash necessary to eliminate SKIM (Sentry Key Immobilizer Module) security function.
2010 & Newer: Generation 4
- DCS currently does not offer technical support on these engines.
We offer this information to make you aware there can be many differences between an Industrial Cummins engine vs. a Dodge Cummins engine. The cost and time switching these engines over can be substantial.
12 Valve Industrial Engines
Details that often differ from automotive style engines:
- injection pump
- timing cover
- turbo inlet/outlet
- throttle linkage & cable
- lower radiator hose nipple
- a/c compressor bracket
- fan support & pulley
- belt tensioner bracket
- oil pan & pickup tube
- exhaust manifold
- air horn
- lower compression ratio
24 Valve Industrial Engines
- Injection pump will not communicate with Dodge ECM
- No electronic tuning capabilities
- Much lower governed RPM is common (as low as 1,900 RPM!)
- fly-by-wire TPS (throttle position sensor incorporated in the accelerator pedal)
- Lower rad hose connection, a/c pump bracket
- Fan support/pulley
- Thermostat housing/alternator mount
- Belt tension bracket
- Oil pan and pickup tube (too long of a sump)
- Exhaust manifold
- Air horn (Intake)
- Factory diagnostics require Cummins Insight®
Possible Options to make an Industrial 24 Valve conversion-friendly:
1.) Use a mechanical injection pump from a 1994 -98 Dodge 12 Valve engine known as “P-pumping” the 24 Valve engine
2.) Get ALL of the DODGE electronic engine components (VP44, ECM, PCM, TPS & throttle cable)
Common Rail Industrial Engines
Our adapter plates will not work with the Common Rail industrial engines due to the engine’s rear-gear timing system.
*Diesel Conversions® is not affiliated with Cummins, Ford, or Dodge. Our uses of these trademarks are for descriptive purposes only.
Diesel Conversion Specialists
A Very Brief History of the 12-Valve Cummins
If you’re a fan of big, North American pickup trucks, you’ve probably heard a thing or two about the Cummins diesel engine used in heavy-duty versions of the Dodge Ram. You may have even heard about what truck fans like to call the “12-valve”. To most people, more valves per cylinder would seem like a good thing. However, the 12-valve Cummins has achieved somewhat of a cult status in the truck scene. The 12-valve is as revered as the 2JZ or the K-series, and some people will even tell you that it’s the greatest engine ever made. Of course, you’re probably wondering why.
First of all, let’s talk about why it’s called the Cummins. The engine is made by Cummins, Inc. of Columbus, Indiana. Founded by diesel mechanic Clessie Cummins in 1919, Cummins has become one of the most respected diesel engine manufacturers in the world. Most of Cummins’ engines are used in heavy machinery, buses, transport trucks, and even as generators. There are few companies that know their way around a diesel engine like Cummins does.
So when it came time for Dodge to up the ante in the world of heavy-duty pickups, they turned to Cummins for help. General Motors had the ultra-efficient Detroit diesel, while Ford had the powerful IDI diesel engine made by International Harvester. Both of these engines were V8 diesels specifically designed for use in a pickup truck as an alternative to thirsty gasoline engines. In contrast, Dodge decided to borrow the existing B Series Cummins engine. The B Series was a straight-six diesel engine widely used in mail trucks, school buses and even in mining operations as generators. It needed to work in the Ram, too—Dodge was already several years late to the diesel truck party.
The first Cummins diesel to be fitted into a Dodge Ram was a 5.9-litre, 12-valve straight-six called the 6BT. From 1989 to 1998, the 6BT would cement its reputation as one of the greatest diesel engines ever made. Fitted from the beginning with a Holset turbocharger (which wasn’t intercooled until 1991), the “12-valve” became a legend for its power, efficiency, and reliability. The Cummins diesel helped usher in a new era of American trucks: never before had the humble pickup been able to work as hard as the Cummins-engined Ram. What made the Cummins so popular was the fact that its peak power and torque was insanely usable—in fact, the redline is only at 3,000 RPM! The 12-valve was able to get respectable fuel economy while producing torque figures never-before seen in an ordinary pickup truck.
By 1998, emissions regulations necessitated the switch from the 6BT “12-valve Cummins” to the ISB “24-valve Cummins”. Although the 24-valve was more powerful than the 6BT and was, by all means, still a very good engine, it never achieved quite the same popularity as the original 12-valve. Today, the 5.9 12-valve diesel is still very much sought-after by truck buyers for its reliability, mechanical simplicity, and efficiency. They are also very popular among enthusiasts, as the iron block can handle a lot of power. Mind you, because it’s essentially a scaled-down dump truck engine, this shouldn’t come as much of a surprise.
By now, I hope that I’ve been able to give you the impression that the 12-valve Cummins is a pretty good engine. But is it really one of the best engines ever made? I think you could make a pretty good argument in favour of the 6BT. From a tuning perspective, the 6BT was simple to work on, capable of handling huge amounts of power, and well-supported by both OEM and aftermarket parts manufacturers. If you could make a roadworthy brick shithouse, the Cummins would probably be the most fitting engine you could put in it. It might not set lap records at the Nurburgring, but if there’s a tree stump that needs to be pulled out of the ditch, a Cummins will probably get the job done.
This content was originally posted by a Car Throttle user on our Community platform and was not commissioned or created by the CT editorial team.
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Cummins 12 valve
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