Getting The Lowdown On EcoBoost Piston Design With Mahle

As we continue to enjoy the horsepower war currently raging throughout the automotive industry, one revelation that often gets buried beneath the headlines of the latest high-buck blown V8 model is that turbocharged, small displacement engines are starting to make some serious power.

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For the vast majority of the five decades that the Mustang has existed, the V8 variant was the model synonymous with performance, while lesser powerplants were relegated to commuter car status. Those days are over with the introduction of the turbocharged EcoBoost four-cylinder, which is capable of dishing out some serious grunt when modified, while also yielding better weight distribution and fuel economy.

It can be hard to maintain perspective when flat-plane crank V8s are revving to 8,200 rpm and family sedans are suddenly available with 700 horsepower, but consider this fact: the 2.3-liter EcoBoost four-cylinder engine offered in the Mustang makes more horsepower than the 4.6-liter V8 that debuted in the 2005 Mustang GT, and it does so while returning more than 30 miles per gallon on the highway.

Perhaps of even more importance to enthusiasts is the fact that these EcoBoost engines have massive potential for performance tuning. With EcoBoost technology now in more than five-million Ford vehicles there are a lot of owners who are ready to ratchet up the output of their engines, and the aftermarket is just starting to dig into these powerplants.

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Whether you’re ready for it or not, small-displacement engines using forced induction are likely to continue to rise in popularity in the coming years. Not only do these engines typically offer a the lower cost of entry to enthusiasts, but regardless of trends, OEMs will continue to gravitate in the direction of this design philosophy in order to satisfy the federal fuel economy and emissions mandates that big-block V8 engines cannot.

But with advanced technology comes potential unfamiliar territory, so we sat down with Trey McFarland at Mahle to get the details on how the specifications of the 2.3-liter EcoBoost requires some unique solutions to piston design, and how Mahle improves upon the OEM piece to offer enthusiasts a product that is ready for just about any engine modification you can throw at it.

Four-Cylinder Revival

The SVO name might not have had the gravitas of the GT, but there was no denying that during its production run, it outperformed the V8 variant both in handling and straight line performance. Image: Ford

The SVO name might not have had the gravitas of the GT, but there was no denying that during its production run it outperformed the V8 variant both in handling and straight line performance. While its reign at the top of the Ford Performance food chain was short, it is fondly remembered by enthusiasts with a penchant for boost. (Photo courtesy of Form Motor Company)

For a brief moment in the 1980s, the Mustang GT was usurped as the most powerful offering the Mustang lineup by the 2.3-liter, turbocharged four-cylinder Mustang SVO. Due to ever-tightening federal fuel economy and emissions regulations, the V8s of the day became more marginalized while turbocharged, small displacement engines continued to grow in popularity as both OEMs and aftermarket companies focused engineering prowess on these suddenly viable engine configurations.

Sound familiar? While factory V8s are offering more power than ever before, there’s no shortage of indicators that point toward big displacement engines shifting toward more of a niche market as OEMs contend with federal mandates — all of which will continue to be increasingly stringent in the coming years.

It’s not by sheer serendipity that Ford has once again turned to a turbocharged four-cylinder powerplant for the Mustang at the cusp of a potential paradigm shift in the industry. This is evidenced by the fact that this boosted four-pot is slotted just below the GT in the Mustang performance pecking order, while the naturally-aspirated V6 serves as the base model. And make no mistake – the EcoBoost 2.3-liter is a trick piece of hardware – and is capable of dishing out quite a bit more grunt than it does in stock form.

But things have changed in the last few decades and the advanced technology behind these engines requires some serious engineering by the aftermarket. “There’s tremendous potential in these turbocharged engines,” McFarland said. “But to get that, it means big boost and some pretty good demands for the pistons. Gone are the days of building a tougher part that simply does the job and puts up with the abuse. These days we need to consider how to design for not only big horsepower, but good fuel economy, longevity and drivability as well.”

Gone are the days of building a tougher part that simply does the job and puts up with the abuse. These days we need to consider how to design for not only big horsepower, but good fuel economy, longevity and drivability as well. – Trey McFarland, Mahle

Yet for the Mustang’s EcoBoost engine, there are a number of unique considerations that go beyond the normal factors of turbocharged four-cylinder performance.

Direct Injection Versus Multi-Port Fuel Injection

While direct injection started making its way into production gasoline engines a few years ago, it’s still a relatively new technology, and with it comes some unique considerations.

As opposed to traditional multi-port fuel injection, which sends fuel into the intake tract or cylinder port by way of a relatively low-pressure fuel injector, direct injection sends highly pressurized fuel from a common rail fuel line directly into the combustion chamber of each cylinder.

Because of this distinction, pistons used in most direct injection engines have some unique design features. “Direct injection is effected by a number of things most people don’t consider,” McFarland notes.

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The key difference between direct injection and multi-port fuel injection is that direct inject engines deliver fuel right into the combustion chamber under exponentially more pressure than the injectors on a traditional fuel injection setup output. That additional pressure causes a lot more heat, which needs to be effectively managed in order to yield reliable performance.

“With most direct injection applications – the 2.3-liter EcoBoost included – there’s an injector pocket in the middle of the piston crown. In a direct injection design, the plug comes in right over the top, unlike an MPEFI engine, and it’s under an incredible amount of pressure,” McFarland explained. “The injector pocket serves to direct that spray correctly into the combustion chamber. It also helps improve emissions by yielding a more complete burn and doesn’t send unused fuel where it shouldn’t go.”

The Anatomy Of A Mahle EcoBoost Piston

Of course, there is more to Mahle’s EcoBoost piston than just the injector pocket in the piston crown. In general, direct injected engines build more heat and temperature-related pressure than multi-port fuel injection engines, and while precise timing and control of combustion in high compression engines like the EcoBoost enables the production of increased power, it also generates more heat that needs to be properly managed to ensure longevity and reliable performance.

The injector pocket is there largely to help optimize fuel distribution. “Once you get to high output, big boost applications, it’s less of a concern,” McFarland pointed out. “But to keep the drivability intact for this particular design, you need that injector pocket.” The shape of the pocket is influenced by a number of factors including, injection timing, pressure, pattern, and spray angle, which adds another set of variables to manage when designing the piston.

The injector pocket is there largely to help optimize fuel distribution. The shape of the pocket is influenced by a number of factors including, injection timing, pressure, pattern, and spray angle, which adds another set of variables to manage when designing the piston.

Numbers Don't Lie: Five-Million EcoBoost Vehicles On The Road

Ford has more than five-million EcoBoost-powered vehicles on the road now, creating quite an incentive for aftermarket companies to develop go-fast parts for these engine designs. Since there’s a turbocharger already in the mix from the factory the natural inclination is to up the boost. But when doing so, it’s important to make sure in the internals can handle what you’re throwing at them, lest you end up with an oil pan full of chewed up components. (Photo courtesy of Ford Motor Company)

“The top ring groove sees a lot of heat in particular,” McFarland explains. “This increases the chances of micro-welding. Extreme heat loads can actually cause aluminum transfer from the ring groove to the ring. If that happens, you’ll get metal transfer that tears the ring up, and causes pitting in the bottom of the ring groove. If you have a ring groove that isn’t flat the seal is lost, pressure moves where it shouldn’t, and the result is an increase in emissions and a loss of power.”

To combat this, the stock pistons have anodized top ring grooves and an anti-friction skirt coating. The Mahle PowerPak performance pistons (PN 197755345) include the same treatment, but also have a phosphate dry film lubricant added for protection against galling in the pin bores. The coatings are key in protecting the pistons for maximum durability, especially the anodized ring grooves.

“The EcoBoost piston profile is slightly different from typical piston profiles because the crown of the piston sees a lot of heat, which in turn translates to increased metal expansion, so we have to account for that as well,” McFarland points out. “If you were to switch from traditional fuel injection to direction injection on a specific engine, the piston profile for that engine – specifically the top of the piston – would have to be smaller in diameter to help manage the additional heat.”

Anodized top ring grooves are necessary to protect the top groove from micro-welding, damage that occurs when metal is transferred from the ring groove to the ring, which results in power loss and blow-by. Mahle pistons have phosphate dry film lubricant added for protection beyond the anodized top ring grooves and an anti-friction skirt coating to provide maximum durability.

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In direct injection applications, managing heat is something of a balancing act. This issue is handled by the piston design and oil squirters, which send oil to the underside of the piston to pull heat away from it. Factoring in the effectiveness of the oil squirter system determines how companies like Mahle design its direct injection pistons, particularly when it comes to profile diameter and expected heat expansion of the metal.

Oil squirters, which send oil to underside of the piston to help pull heat out of the piston, are very common — not only on direct injected engines like the EcoBoost, but high-performance fuel injected engines that tend to generate a lot of heat as well, such as the GM LSA V8.

But when it comes time to select an aftermarket piston, McFarland cautions that not all pistons are created equal.

“OEM piston design is dramatically better than it was 20 years ago, so throwing a random aftermarket piece in the mix isn’t necessarily going to yield the result that an enthusiast wants from the modification,” McFarland said. “These designs have become more nuanced to specific applications. At Mahle, we’ve seen that added strength, OEM-level longevity and compression ratio changes are the features that performance customers are looking for. We start with a highly advanced forging process, increase the ring land and cross-section thicknesses as we do with most applications, and design our pistons with a number of special considerations for the particular application.”

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Does the fairly unassuming appearance of the EcoBoost Mustang – with its lack of 5.0 badging credibility – make this the ultimate modern sleeper? Considering the power these four pot engines can generate when modified correctly (while still sounding like a 2.3-liter engine), the answer might be waiting for you at the next stop light.

While McFarland points out that much of the EcoBoost’s design follows the lion’s share of standard design logic behind direct injected, turbocharged engines – and that means there’s a ton of potential for big power – there’s also plenty of room for major mechanical failure if the internals used aren’t up to the task.

“Ford’s 2.3-liter EcoBoost engine is capable of generating horsepower levels in the range of even the most powerful V8s,” McFarland said. “Pistons like our PowerPak offerings are for those who want to leave nothing to chance.”

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About the author

Bradley Iger

Lover of noisy cars, noisy music, and noisy bulldogs, Brad can often be found flogging something expensive along the twisting tarmac of the Angeles Forest.
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