Piston Options and Opportunities
By Doug Kaufman
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: to quote Engine Builder columnist and performance expert Len Emanuelson, 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.
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?”
Trying to pin the 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.
New and Hot
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.
“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.”
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.
“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.”
In addition, King agrees with others that American muscle is a hot topic and with the theme of restoration that runs through this issue of Engine Builder, it couldn’t be more appropriate. “We continue to see piston sales for vehicles we stopped selling brake pads for a long time ago.These engines typically go through several life cycles, but the older they get, the more quality-oriented their owners become, and they tend to specify a premium part.”
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.”
Silvers says in addition to the pistons for the 348/409 Chevy, Flathead Fords, Nailhead Buick and Chrysler Hemi that his company normally produces, pistons for the 1968-71 Olds 350 V8, 1962-65 Ford 260, 1964-67 Dodge 273, Buick 225, 300 and 340 and Pontiac 326 as well as the 1971-74 AMC 401 are in stock. “We’re trying to stay up with the demand in the market, and that means producing them like the OEM did,” he explains.
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.”
Of course, change can be very good for our business and offering a range of products to meet your customers 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 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.”
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 6 years ago, we started a forging line, so now we have a variety of products to meet customers’ needs, from hypereutectic to forged.”
Hypereutectic cast pistons were introduced nearly 20 years ago 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 piston let engine builders fit the bores better.”
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.”
In the aftermarket, Frank acknowledges the need for precision. “The machining process does need to be more consistent when you’re using a hypereutectic product because you’re starting with a closer piston-to-wall clearance. It can be a little more challenging for a non-sophisticated shop to install hypereutectic pistons, but truthfully, the leading PERs and custom rebuilders recognize the value of hypereutectic and that’s all most will use in their later model engines.”
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?
“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.
“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.
“That’s the beauty of our market,” says Sulprizio. “It gives people the chance to work with a variety of parts. Crate motors, for example, take that away, and require builders to work with very carefully specified parts. When people REALLY want to put an engine together, however, they want to have a variety of choices.”
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.
“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 in to 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.”
Future designs are made possible thanks to the advent of CNC machining. “Engine builders are demanding extremely tight tolerances and finishes along with a reasonable delivery time,” affirms Ross’ Madsen. “This is only possible with today’s high-end CNC machining centers. The days of ‘looks good from here’ are over. Holding tolerances in the millionths is no ‘lip service’ many engine builders have access to very sophisticated metrology equipment and are able to verify tolerance claims.”
Diamond’s Beaubien explains that the manufacturing process has been streamlined by CNC machining, resulting in a better product. “We are able to do consistent mill-unders on the crown. In the past, whether the piston was cast or forged, if you just left the underside of the crown alone, it would be rough and inconsistently thick. CNC has made it so much easier to make it uniform under the crown, balancing it out, eliminating stress risers without sacrificing structural integrity.”
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 5-7 years,” explains F-M’s Frank. “Now, those dates are 3-5 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.”
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. 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 5 years.”
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 right application.”
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.”
Designing pistons within the parameters of the other components will require manufacturers to be more flexible than ever.
“Working with ‘systems’ is definitely desirable,” explains MAHLE’s McFarland. “Unfortunately, the piston is too often one of the last pieces of the puzzle to pull the whole combination together.”
So with the combination of changes at the OE level, new requirements at sanctioning body levels and challenges on the economic front, what does the future hold? “Growth in the piston business is going to come from a lot of different places,” says KB’s Sulprizio. “We see more smaller segments not necessarily huge business from a single area but from lots of niches. But we still see that as good business and we’re tooled up to meet those needs."
Those areas of growth may be smaller slices, but when you add them all up, they still make a pretty good size pie.
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