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Proper Piston Replacement

While the “Fast and the Furious” crowd may have lost interest in the sport compact market, interest in the cars hasn’t dropped off completely.

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By Doug Kaufman, editor, Engine Builder magazine, a sister publication of Underhood Service

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The sport compact market, it was thought, was going to breathe new life into the performance engine market, and for many years, the rapid growth of the market seemed to indicate that there was no limit to how big those little engines could get.

Then something happened: the “Fast and the Furious” crowd suddenly lost interest. The glamour of adding big wings and big tail pipes as well as neon lighting and slamming the suspension seemed less interesting to much of the country.

But, even as the rabid frenzy has died down and certain organizing bodies have dropped out of the market segment, interest in the cars hasn’t dropped off completely.

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For piston manufacturers, keeping up with what’s current as well as what’s coming, requires both fine analysis and a big picture perspective.

“The ‘Fast and the Furious’ set has grown up and the fadboys are gone,” says Brian Nutter from Wiseco. “It’s settled to a sustainable plateau now. Our lineup has matured at this point, but we’ll continue to release pistons for the new ‘hot models’ that are released every year.”

The sport compact world is still alive, says Ross Pistons’ Chris Madsen, “but it’s not quite the same as it was five years ago. For example, there’s not just racing against each other anymore, there’s racing in heads-up venues like the American Drag Racing League, the Street Car Super Nationals and the Outlaw 10.5 classes of racing where big-inch V8s are the norm. Not many years ago, would anyone have imagined sport compacts competing — let alone holding their own or winning — against the likes of nitrous-breathing, blown or turbocharged V8s?”

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Trying to pin the performance market down to a single segment is the surest way to be confused, because there are so many ways the American racing enthusiast has to scratch his itch. And for the piston manufacturers interviewed for this story, each one of those ways has different technical requirements and technological opportunities.

Hot ‘n New

Despite its reputation as a “bolt-on, poser” sport, the sport compact market did introduce a new generation of young people to automotive performance. Now that many of those drivers have matured, what’s next for performance? As always, what goes around comes around.

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“The GM LS1 and the modular Fords seem to be the new American muscle car engines,” says Ron Beaubien of Diamond Pistons. “And once again, Camaros and Firebirds are playing a role. They haven’t built them for awhile and they’re starting to show up on the used car lots, so younger guys can afford them. They take well to modifications, there is so much aftermarket equipment — it’s an easy deal to build them up thanks to all the stroker cranks and rods and, yes, pistons available for them. You can put together a monster pretty quickly.”

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Trey McFarland, of MAHLE Motorsports, agrees that American muscle is still popular. “For at least the near future, the small block GM is still king, with big block GM and small block Ford following. The GM LS family and L92 series of engines is showing the strongest growth from a single category.”

Though the small block Chevy continues to reign supreme, KB Piston’s Scott Sulprizio agrees that huge changes are coming for Ford and Mopar fans. “The sky’s the limit for Fords, and with the new Hemis, Chrysler is an up and coming market.

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“The beauty of our market,” continues Sulprizio, “is its diversity. Whether it’s in sport compact, IMCA modifieds, SCCA or NHRA, we’ve seen things continuing to change. As manufacturers, we have to be ready for those changes.”

Federal-Mogul’s Raymond King says light-duty diesel pistons are finding their way into the performance mix these days as well. “It’s either because they’re seeing lots and lots of road miles as true work vehicles or owners are looking for performance improvements — and diesel performance is a definite market category.”

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Demand in the market is what drives the development of pistons from Egge Machine Company. “Companies have to advance in various ways to keep up with the demands of their markets,” explains Egge’s Ernie Silvers. “For us, we continue to maintain the way things used to be because that is what fits our market. We produce cast pistons for vehicles if they are no longer available in the traditional aftermarket and if enough people ask for it. In the past 12 months, in fact, we’ve added nine new part numbers for a number of vintage engines thanks to customer requests.”

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Design Integration/Product Specification

“When the original equipment manufacturer designs an engine, it develops all of the parts to be integrated into the design,” explains Sulprizio. All of the internal components — from cylinder heads to pistons to connecting rods, valves, camshafts and gaskets — are designed to work in harmony to produce the greatest performance, most fuel economy or whatever combination of the two the OEM desires.

“What we do in the aftermarket,” says Sulprizio, “is essentially the reverse. We find people changing the rods, valves and heads, literally, everything in the motor. They take what the OE determined worked best and become the engineer themselves. For a piston manufacturer, this requires us to meet a broader set of needs.”

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Of course, change can be very good for our business and offering a range of products to meet your customer’s demand is vital. But how do you choose? The question “forged or cast?” continues to rage. It’s a more complicated question than you might imagine and the answer depends on each application.

Forged pistons are recognized as the absolute strongest products available, capable of standing up to nearly anything. “Wiseco’s motto is ‘forgings designed around pistons rather than pistons designed around forgings,’” says Nutter. “We feel this gives the customer the best strength-to-weight ratio at the best price.”

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Ross’ Madsen agrees that aluminum forged pistons are the best material available for mid- to high-power race engines. “I believe 2618 T-61 aluminum is very strong yet pliable and forgiving. In cases of detonation, 2618 is able to flex, give and dissipate heat under the extreme pressure spikes unlike other materials. That’s not to say it’s bullet-proof, but the life expectancy is much higher.”

KB’s Sulprizio says his company’s history (founded in 1922 as United Engine Machine Company by his grandfather) has been in developing and manufacturing cast pistons. “About six years ago, we started a forging line, so now we have a variety of products to meet customers’ needs, from hypereutectic to forged.”

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Hypereutectic cast pistons were introduced nearly 20 years ago for OEM engines that required something stronger than an ordinary cast piston. Hypereutectic alloys contain a much higher level of silicon than in a typical cast piston alloy, providing additional strength and reduced thermal expansion — in other words, the hypereutectic piston, thanks to its higher silicon content, will expand less when the engine reaches full operating temperature.

“The higher silicon content allows the piston to be machined to a tighter tolerance when cold, explains Federal-Mogul’s Tim Frank. “Because the steel of the cylinder bore typically expands at a different rate than the aluminum of the piston, hypereutectic pistons let engine builders fit the bores better.”

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F-M’s King says that most pistons used by OEMs today are of the hypereutectic type. “This allows better noise control, and gives advantages in ring designs and fuel emissions
standards.”

Sulprizio points out that castings offer significant benefits for people who want low thermal expansion. “It doesn’t have the ductility of the forging, but for people who are really good at managing their motors, it’s a product you can race with tight tolerances.”

The question on everyone’s mind, Sulprizio acknowledges, is “How much horsepower can this piston take?” Because forged pistons have the “strength” label, does that mean hypereutectic are weak?

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“I look at it this way: 20 years ago, the OEs couldn’t put out twin-turbos or other exotic engine components and have them effectively managed on the street. Today, however, turbos, small-displacement motors and high horsepower is the norm. The difference? The computer.”

Today’s computer-controlled engines are more carefully and precisely managed, allowing a greater range of performance than ever thought possible. “I try to describe it to people who want to just talk horsepower like this: ‘It’s really what you can manage. I can’t tell you you can’t make 400-500 hp with a hypereutectic piston, because if you can manage the rest of the engine you certainly can,’” says Sulprizio.

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“The OEs have improved their management — they’re running cast pistons yet they’re making more high horsepower, high-output, small motors than ever before,” he says. “It’s how well you play the engine management game.”

Because both KB and Federal-Mogul supply forged pistons as well, representatives from both companies take pains to explain that applications for both exist, and that proper selection comes down to recognizing the ultimate requirement of the engine.

What’s the Buzz?

Even with the surge of nostalgia vehicles and restoration engines, advancements in internal engine components continue to be made. Those changes are certain to affect the piston of the future, in both gas and diesel applications.

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“One of the more interesting changes that is just over the horizon will be in piston crown configuration for direct injection, non-auto ignition applications,” says MAHLE’s McFarland. “On a direct injection diesel piston the crown of the piston also acts as the combustion chamber and normally has an easy-to-machine round-shaped bowl. The direct injection, non-auto-ignition engines often have a deflection ridge designed to promote more complete atomization. This ridge, in most cases, requires 3D milling and a number of variables come into play when designing the shape (injection timing, duration, psi, rpm, boost psi if applicable). The proper design of a direct injection piston auto-ignition (diesel) or non-auto-ignition is considerably more involved.”

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Future piston designs will absolutely feature deck thickness requirements, says Wiseco’s Nutter. “Different forging designs have different deck thickness requirements because the structure underneath really serves to support it. The smaller the unsupported area, the thinner it can be.”

For a company like Federal-Mogul, which develops pistons for both OE applications and the aftermarket, the development of new designs can be years in advance of their actual production — but that time frame is shortening. “A few years ago, the typical window of development for new products was five to seven years,” explains F-M’s Frank. “Now, those dates are three to five years out and the OEM is always pushing to reduce development time even further. The shift is definitely toward piston architecture: the piston designs are becoming more ‘deliberate,’ especially where the surfaces bridge and carry stresses better without adding weight.”

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Of course, if it’s seen first at the OE, eventually it will find its way to the aftermarket. And, luckily, the aftermarket continues to be up to the challenge.

“Skirt coatings, offset pins, Nitrided/Napier rings were happening for us from 2002 to 2008 and, at this point, we consider these features ‘standard’ rather than ‘trick,’” says Nutter.

“The change over to direct injection is going to be a hurdle that tuners haven’t seen since the early ’80s,” Nutter continues. “The VVT systems are a small hurdle for the domestic engine builders — but Honda and BMW builders work with it every day and everyone will have a good understanding of tuning it within five years.”

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Coatings will continue to play an important role in piston design and development. “There are a lot of coatings available and most have some benefit for some applications. The most widely used are anti-friction skirt coatings that reduce frictional drag. MAHLE’s Grafal anti-friction skirt coating is also a compressible membrane that has a unique cushioning property that greatly eliminates the metallic contact between the piston skirt and the bore,” says McFarland. “Thermal barrier coatings on the crown are becoming popular, but there are a number of different types with different benefits and it is important that the right coating is used for the right application.”

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Federal-Mogul’s Scott Gabrielson explains that as performance goes up, the piston tends to run hotter. “Our Thermo-Shield coating on the top crown, top ring groove or both can reduce microwelding between the piston and ring. Certain applications, such as the Ford 4.6L in the Mustang and the old supercharged Buick 3.6L engine are particularly prone to the microwelding condition.”

The advancements in coatings have been helpful, Diamond’s Beaubien says, because the base materials have stayed the same despite increases in power demands. “It’s like a finely tuned piano,” he says. “Everything has to work so well together. The wave of the future is narrower rings, narrower radial widths, thinner oil rings that free up friction while reducing radial tension and making more horsepower. Pistons are more structurally sound and a lot lighter. Keeping up with the cylinder head designs will continue to be a challenge.”

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While piston-makers believe growth in the market will continue, they’re finding that designing pistons within the parameters of the other engine components will require manufacturers to be more flexible than ever.  

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