After we made our 6.0L vs 7.3L Powerstroke article, it became very apparent that there is a surprising amount of 6.4L Powerstroke fans out there who wanted to see a similar video. Both the 6.0L and 6.4L Powerstroke are arguably some of the most problematic diesel engines of all time, however, they both have a lot potential when modified correctly, so let’s dive in and figure out which one is better.
It would probably be an understatement to say the 6.0L Powerstroke is one of the most hated diesel engines of all time. It was riddled with problems when compared to the older 7.3L Powerstroke, however, with the right modifications it was a decent engine, but ultimately, Ford had to stop placing the 6.0L Powerstroke in their heavy-duty trucks for a few reasons, mostly due to emissions and power output.
Although Ford and Navistar’s relationship began to breakdown because of the issues with the 6.0L Powerstroke engine, they still ended up working together to produce the 6.4L. The 6.4L’s architecture was similar to the 6.0L’s and they share a lot of similarities, but there are quite major differences. A lot of the changes on the 6.4L were put in place to improve emissions, which get stricter nearly every year.
Eventually, the design flaws and endless warranty claims associated with the 6.0L and 6.4L engines forced Ford to ditch Navistar and bring their diesel engine program in-house for the 6.7L Power Stroke, but that’s a discussion for a different time.
Both engines use a 4.13-inch stroke, however, the 6.4L uses a larger 3.87-inch bore, which is what allows for that extra 400cc of displacement. Of course, that larger bore requires a completely different piston which is one of the major problems with the 6.4L, but we’ll get to that later. They both use a cast-iron block with cast iron heads, 4-valves per cylinder with a single cam in the block.
One of the biggest and most notable between these two engines is the injection system. The 6.0L uses a revised version of HEUI injection similar to that of the 7.3L, but unlike the 7.3L, the system used on the 6.0L is full of all sorts of issues.
The 6.4L, on the other hand, uses a common rail injection system with advanced piezoelectric injectors and a high volume K16 VDO injection pump. Unfortunately, the 6.4’s injection system is also full of major problems and can lead to several catastrophic failures in the engine.
As we’ve discussed in previous articles, the 6.0L was the first Powerstroke engine to receive a variable geometry turbocharger. The variable turbo gave it good throttle response and tons of low-end torque while still maintaining good top-end power. This works by using electronically controlled vanes in the exhaust housing which change the effective internal size of the exhaust housing, which ultimately changes exhaust gas velocity. Unfortunately, the variable turbo on the 6.0L was known for being a little problematic.
When Ford and Navistar moved from the 6.0L to the 6.4L, they introduced a compound turbocharger setup, which combines two turbos in series. This compound system was manufactured by BorgWarner and combined a 65mm fixed geometry turbo with a 52mm variable geometry turbo. When combined these turbos produced over 40psi of boost in totally stock form. One of the nice features of the compound turbo system is its potential to support nearly 600whp.
Part of the reason Ford killed off the old 7.3L Powerstroke was that it wasn’t meeting emissions standards, and the 6.0L was the first Powerstroke to feature an exhaust gas recirculation system. The EGR system does a good job of reducing emissions output, however, its not the most reliable system in the world.
Moving to the 6.4L, emissions standards were getting hard to meet, so Navistar simply added another exhaust recirculation system and a better EGR cooling system. Approximately 25 percent of all the air a 6.4L breathes in contains exhaust gases, and although Navistar tried to fix the EGR issues of the 6.0L, the 6.4L was still known for suffering from EGR issues.
The top end of the 6.0L is where many of the most major problems occur. The 6.0L uses four torque-to-yield head bolts per cylinder and the head bolts are only 14mm in diameter, which ultimately allows the head bolts to stretch under high pressure and lead to blown head gaskets. Once the heads are pulled to install new head gaskets, it’s common to find numerous cracks in them.
The by the time the 6.4L rolled around, Ford and Navistar had realized the head gasket issue of the 6.0L and it’s not a problem which plagues the 6.4L. That being said, the 6.4L still suffers from cracking in the heads, but it’s not as common as it is on the 6.0L. The major weak point of the 6.4L is the valvetrain, where the rocker arms can suffer from excessive heat and wear due to lack of oil supply.
Bottom End Strength
The bottom end is one of the areas the 6.0L is pretty decent. The pistons and rods are well known for holding up to extreme mileage and are capable of withstanding upwards of 800whp. The crankshaft is secured with a bedplate which makes the bottom end extremely strong. To put it simply, the bottom end of the 6.0L is one of its better features.
The 6.4L’s bottom end is one of its weak points. To be fair, the connecting rods and crankshaft on the 6.4 are very strong and they’ve been proven to be capable of holding up to 900whp, but the pistons are a different story. Due to excessive cylinder pressure, age, abuse and a design that retains heat, the pistons are prone to cracking in both stock and modified applications. As you can imagine, a cracked piston isn’t an easy to job to fix and can be incredibly expensive.
- 6.0 Pros vs 6.4 Pro
- 400whp+ with tuning vs 550whp+ with tuning
- Bed plate vs bed plate
- Rotating assembly can handle 800whp vs rods with can handle 900whp
- 6.0 Cons vs 6.4 Cons
- Lots of EGR issues vs less EGR issues
- Stretched head bolts lead to head gasket issues vs piston cracking
- VGT sticking vs cab needs to be removed for many repairs
- DPF failure vs HPOP failure
- Both suffers from cracked heads
Unfortunately, both of these engines are plagued with various issues, and there are more problems than what we’ve discussed in this video. The important thing to remember here is that both engines have a decent amount of potential once the most common issues are fixed with aftermarket parts. At the end of the day, both of these engines were so unreliable and bad that Ford ended up developing the 6.7L without Navistar.
That being said, the question remains: which one is better? I think which one is better depends on what you’re willing to do to make the engine reliable. The 6.0L needs a bulletproof kit to become reliable, where the 6.4L will end up needing new pistons. Both engines are pretty stout, with the 6.4L’s factory compound turbocharging system having more potential once the pistons are replaced.