Performance Roadblocks of the 6.7L Power Stroke
As newer, more powerful diesels have come to market, it stands to reason that the amount of performance you can squeeze out of them beyond stock has gone up significantly. In a continual effort to meet stricter emission standards while also accommodating the customer’s lust for “best-in-class power ratings, compression-ignition engines now come with higher pressure injection systems, better turbo technology and stronger hard-parts than ever before. However, there can be exceptions to this rule, especially when the manufacturing of an engine changes hands. Case in point, the fallout from all the reliability problems surrounding the Navistar-produced 6.0L and 6.4L Power Stroke culminated in Ford taking its engine program in-house. Under the FoMoCo umbrella, a vastly different V8 diesel power plant emerged. It made more horsepower and torque in factory form than the 6.4L did, but some of the stock components didn’t support the kind of performance truck owners had grown accustomed to with the previous Power Stroke.
In the early years, a restrictive OEM turbocharger limited the 6.7L Power Stroke to a horsepower wall of 500rwhp or less. The answer back in 2012-2013 was to replace the stock turbo with a fixed geometry unit with a larger compressor wheel. But with the airflow issue solved, the next roadblock surfaces: the factory high-pressure fuel pump (the CP4.2) can’t support an all-out effort from the injectors, namely when hot tuning files command longer injector duration (i.e. injector on-time). Not to worry, a second pump can be installed and it’s game-on until 600 to 650rwhp. Then the second-generation 6.7L Power Stroke changed everything when it arrived in ‘15. A better turbo, larger displacement CP4.2, and higher-flowing injectors—each of which can be retrofitted onto older engines—was all part of the package.
Below, we’ll walk you through the performance roadblocks the ’11-’14 and the ’15-’19 6.7L Power Stroke face, as well as how you can get around them.
Roadblock #1: OEM Turbocharger
Like any Power Stroke, significant gains can be had by recalibrating the powertrain control module (PCM). Just like the first horsepower hurdle the 6.4L Power Stroke encounters, the 6.7L Power Stroke runs out of air via turbocharger long before the injection system has given all it has to offer. The turbo limitation is especially harsh on ’11-’14 engines, which were equipped with the Garrett GT32 SST, a variable geometry turbo featuring dual 46mm compressor wheels (inducers) and a dinky single 64mm turbine (inducer). 2011-2014 model year Super Duty’s rarely crest the 500rwhp mark thanks to the GT32 SST.
New Turbo in ‘15 Allows For 540rwhp
Beginning with ’15 model year engines, which also came with a longer stroke CP4.2 and revamped injector nozzles, a single compressor wheel VGT from Garrett’s GT37 family of turbochargers debuted. Its larger compressor (61mm inducer) and turbine wheel (72mm inducer) plays a key role in ’15-’19 trucks making 540rwhp on tuning alone. Still, given the untapped potential of the new style CP4.2 and especially the injectors, the turbo remains the key barrier to more horsepower on the 6.7L Power Stroke.
GT37, Retrofit Kits & Upgrades
Taking advantage of the improvements made to the second-generation 6.7L Power Stroke, the aftermarket set to work swapping the new-style turbo and larger displacement CP4.2 onto ’11-’14 engines, which yielded solid gains. Not only does saddling a first-generation 6.7L mill with a late-model pump and turbo push an ’11-’14 Super Duty past 500rwhp, but the turbo can be upgraded at any time with one of the many aftermarket drop-in options that are available. When adding a 63mm or 64mm version of one of the latter options to a ’15-’19 truck, 600rwhp is possible. Fleece Performance Engineering and Midwest Diesel & Auto have both worked some pretty impressive magic on the factory-based, GT37 platform.
Breaching 600rwhp With Compound Turbos
One way to blow past the 600rwhp threshold without upgrading the factory turbo on a ’15-’19 6.7L Power Stroke is to add a second, larger turbo to the equation. We’ve seen No Limit Fabrication’s compound arrangement support 625rwhp by combining a 76mm Precision Turbo & Engine atmosphere charger with the stocker. In the configuration shown above, the factory CP4.2 and injectors went untouched and the truck ran squeaky clean and extremely strong.
Roadblock #2: The CP4.2
The Bosch piezo injectors used in all 6.7L Power Stroke engines are quick-firing and capable of supporting big horsepower (700+ rwhp). However, the factory CP4.2 isn’t capable of maintaining adequate rail pressure when max effort PCM tuning calls for longer duration (again, injector on-time). To get around this, a second high-pressure fuel pump (typically a Bosch CP3) can be added to the 6.7L Power Stroke and belt-driven from the second alternator’s location. The other alternative is to replace the stock pump with a stroker CP4.2 from Exergy Performance or RCD Performance.
750rwhp on Stock Injectors
Once the CP4.2 situation is addressed, either by installing a stroker version or adding a second injection pump, the true potential of the factory injectors can be unleashed—and it’s enough to bend connecting rods (more on that below). Incredibly, with the right air in the mix as well, the stock injectors can support more than 700rwhp. Equipped with Exergy Performance’s 10mm stroker CP4.2 and No Limit Fabrication’s compound turbo system (which entailed a 63mm Fleece VGT in the valley and a 76mm Precision turbo out front), several late-model Super Duty’s have put down between 730 and 750rwhp. At this point, and thanks to having in excess of 60 psi of boost on tap, ARP head studs should definitely be considered.
Roadblock #3: Factory Connecting Rods
It’s more extensive and expensive to get around this particular roadblock. Unfortunately, the connecting rods used in the 6.7L Power Stroke are thinner and nowhere near as strong as the units found in the 6.4L. However, they’ve proven capable of living lengthy lives in 650rwhp applications and can even survive 700rwhp with good PCM tuning. Beyond that point, you are likely on borrowed time.
Aftermarket Rods Are the Only Way Forward
At the factory level, very few connecting rod changes have taken place for the 6.7L Power Stroke between ’11-’19. In January ,2016 the wrist pin diameter increased to 35mm from 34mm. After that, updated connecting rods made their way into the Job 2 engines destined for ‘17 trucks, but the verdict is still out as to just how much more horsepower and torque they can handle, if any. If you’re in the middle of preparing an engine build, it’s best to fork over the cash for a set of aftermarket rods. Carrillo, RCD Performance and Wagler Competition Products all make a solid product.
Big HP Solution for Stock Rods
While a stock bottom end 6.7L Power Stroke can make considerable power with an upgraded high-pressure fuel pump and compound turbos feeding it, pushing 700rwhp or venturing beyond it puts the owner in no man’s land. For ’11-’19 Ford owners not looking to push the limits of the stock rods, a single, large frame fixed geometry turbo such as a BorgWarner S400 is a sound option. A big single won’t offer the kind of drivability a set of compounds will, but the lower peak torque production and drive pressure created by the S400 will keep the rods alive much longer.
The Heads and Valvetrain Have Proven Solid
Though the 4-valve, reverse-flow aluminum heads aboard the 6.7L Power Stroke aren’t known to be a major point of restriction, several companies offer CNC porting which is said to yield gainful results. In the 700rwhp and less realm, the stock heads will support power just fine, but it’s wise to upgrade to stiffer valve springs and chromoly pushrods should you ever need to venture under the valve covers.
Curious what horsepower obstacles you’ll have to overcome with your 6.0L Power Stroke? Find out right here.
