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Performance Roadblocks of the 6.0L Power Stroke

After exposing the performance obstacles that keep the 7.3L from living its best life, we decided to move on to its successor, the 6.0L Power Stroke, to shed some light on its horsepower barriers. Like the 7.3L, the 6.0L makes use of a HEUI injection system, but that’s not this Power Stroke’s biggest performance hindrance. In fact, the 6.0L’s block, rotating assembly and cylinder heads can support roughly 700rwhp in stock form. No sir, this Navistar-built V8’s biggest horsepower handicap is its lack of head-to-block fasteners, as well as the type of fasteners they are. At power levels barely beyond stock, their inadequate clamping force can earn you a blown head gasket, maybe even two.

Plagued by head gasket, EGR and oil cooler problems, it’s no wonder most 6.0L Power Stroke upgrades are geared more toward reliability than they are about breaking through a horsepower wall. But once the engine is studded, you can turn the second-generation, higher-pressure (yet somewhat fragile) HEUI system loose—so long as you maintain a strict maintenance regimen. By simply practicing 5,000-mile oil changes and running a quality oil you won’t have to say goodbye to your injectors 100,000 miles too early. Not unlike the 7.3L, you’ll have to address the issue of airflow. While the 32-valve heads flow well, the factory variable geometry turbocharger becomes a restriction before you can even knock on the door of 500rwhp.

To eliminate a few of the 6.0L’s most notorious failure points and chase your horsepower goal in an unimpeded manner, check out the performance roadblocks you’ll be met with—along with the ones you can avoid—in the article below.

Head Gaskets, Head Gaskets, Head Gaskets

6.0L Power Stroke Blown Head Gasket

Focusing solely on the areas that limit horsepower on the 6.0L Power Stroke, surprisingly there aren’t very many of them. For example, the heads can support as much as 700rwhp in factory form, the rods are capable of handling the same, a bed plate means the 6.0L has never heard of main cap walk and the high-pressure oil pump can support a sizeable injector upgrade. However, pushing further than the 325 hp these engines left the assembly line with can lead to head gasket issues in short order—and at least a week of downtime at a reputable shop to fix the issue.

Roadblock #1: TTY Head Bolts (and Not Enough of Them)

Power Stroke Diesel Head Bolts

So why do the 6.0L’s heads lift so often? It’s a toxic combination of a lack of fasteners and the fact that the engine uses torque-to-yield head bolts. Not exactly undersized, the 14mm diameter of the head bolts would seem sufficient (even overkill) in comparable engines, but there simply aren’t enough of them on the 6.0L. Just four fasteners surround each cylinder, with the inner head bolts having to share the clamp load with the neighboring cylinder. And, once a torque-to-yield fastener stretches, it becomes permanently lengthened, effectively losing its original clamping strength.

ARP Head Studs

ARP Head Studs Power Stroke Diesel

Mod for mod, you can make significantly more power with the 6.0L Power Stroke than you can with the 7.3L, but it’s wise to address the head bolt issue before you get started. Meet the best-selling fastener in ARP’s long and storied history: the ARP2000 head studs produced for the ’03-’07 6.0L Power Stroke (PN 250-4202). They offer improved engagement by threading deeper into the block and offer a tensile strength of 220,000 psi. For even more clamping force, ARP’s Custom Age 625+ studs offer a minimum tensile strength rating of 260,000 psi.

Beyond Head Studs

O-Ringed Power Stroke Cylinder Head

ARP2000 head studs help and Custom Age 625+ studs are even better, but if you’re going after big power with a 6.0L you better O-ring the heads. While this step is cost-prohibitive for most 6.0L owners, for those that plan on their engine seeing high boost and elevated cylinder pressure it’s well worth it. Some mildly modified 6.0L owners opt for O-rings during a head gasket and head stud job for ultimate peace of mind, although it isn’t necessary in sub-700rwhp setups. By far, the most important part of keeping head gaskets alive has to do with the heads and block being flat. Moral of the story: use a good machine shop.

Roadblock #2: Oil Quality

5W40 Diesel Engine Oil

This one is all up to the end-user and how well he or she takes care of the 6.0L engine. Remember, like the 7.3L the 6.0L is equipped with HEUI, which means it relies on engine oil to actuate the fuel injectors. However, the 6.0L sees higher injection pressure than the 7.3L does (ICP can reach 4,000 psi vs. 3,000-3,200 psi on the 7.3L). In an emissions-compliant engine, the oil has its work cut out for it even more thanks to EGR contaminating the oil with soot deposits. This means you need a quality engine oil, and it needs to be changed according to Ford’s “severe condition” interval, which is every 5,000 miles.

Poor Maintenance Kills Injectors

HEUI Diesel Fuel Injector

The 6.0L’s HEUI system has no issues maintaining adequate high-pressure oil with larger injectors in the mix, but a lack of maintenance will cut their life short indefinitely. For example, dirty engine oil is one of the primary culprits in the phenomenon known as stiction. Engine oil that’s wrought with carbon deposits and other contaminants leads to coking inside the injectors, which causes friction and eventually hampers the injectors’ operation. Remember, at full steam ahead the 6.0L moves 18 gallons of oil per minute, the oil gets pressurized as high as 4,000 psi in the high-pressure circuit and is also routed through a very restrictive oil cooler that’s prone to failure, so don’t skimp on the oil’s quality or neglect that 5,000-mile change interval we talked about above.

Roadblock #3: Factory VGT

Garrett VGT Turbocharger Power Stroke Diesel

The 6.0L’s variable geometry Garrett GT3788VA is quicker to build boost than the fixed geometry GT38 and GTP38 found on the 7.3L Power Stroke and can also support 100 more horsepower, but eventually it becomes too much of a restriction in the horsepower-making puzzle. Like all factory turbochargers, the original unit can only be leaned on so far before it’s out of its efficiency range. For the 6.0L, the GT3788VA can support 450 to 475rwhp, but it’s screaming at this point—not to mention it’s moving a lot of hot air. As you get into the 500rwhp range, the drive pressure to boost ratio is getting out of hand also.

Another Roadblock for the Factory Turbo

Unison Ring 6.0L Power Stroke Turbo

A “sticking turbo” is one of the most common reasons a 6.0L Power Stroke loses power. When the unison ring that controls the movement of the variable vanes within the turbine housing binds up or seizes in place due to carbon and soot buildup, the vanes can no longer optimally route exhaust gases across the turbine wheel. For the driver, this equates to poor drivability and usually trips an underboost code. Luckily, gearheads that drive their trucks hard rarely experience the failure. Owners that do a lot of steady-state (highway) driving see it the most.

A Wealth of Turbo Options

Elite Diesel Powermax SSX Turbocharger

One of the easiest ways to make solid power with the 6.0L Power Stroke is to ditch the factory VGT in favor of a fixed geometry turbo. Popular swaps include the use of BorgWarner’s T4 S300 and S400 series chargers (typically the latter for making big power) and we’ve seen 700rwhp or more made on various builds. However, and unlike with the 7.3L Power Stroke, there are a host of viable drop-in, factory-appearing turbos that move enough air to support 625rwhp or more. Some of the big players in the VGT game are RCD Performance, KC Turbos and Elite Diesel Engineering.

After Studding the 6.0L, it’s Open Season

2003-2007 6.0L Power Stroke Diesel Engine

Once the head bolt situation is ironed out, a bigger turbo and injectors can go in and the rest of the factory long-block can be leaned on quite heavily for more power. In the photo above, an ’03 6.0L Power Stroke fitted with ARP Custom Age 625+ studs, 190/100 injectors and a bolt-on 64mm Powermax-SSX variable geometry turbo from Elite Diesel Engineering (hidden back in the factory location) made more than 550 hp and 1,000 lb-ft on the chassis dyno. If the truck hadn’t been conservatively tuned to keep the 5R110 transmission alive, 600rwhp might’ve been on the table.

Not sure how to get started in your quest for more power? Check out our budget diesel mods list for the 6.0L Power Stroke right here!

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