Asking piston manufacturers “what’s new” reveals a number of trends that are reshaping the piston business today. One is that there’s no longer a time lag of three or four years for aftermarket piston suppliers to tool up for the latest piston applications. Production engine remanufacturers (PERs) and custom engine rebuilders (CERs) are asking for pistons to fit current model engines the same year a new engine is introduced. That’s a challenge for aftermarket piston suppliers because it takes time and money to tool up for new pistons. If the company is not an original equipment supplier, it can be an expensive investment. Consequently, piston availability continues to be an issue for some late model engines.
The good news is that piston manufacturers are now making more standard sized pistons available for older engines. Previously, most aftermarket piston suppliers only offered oversize pistons to accommodate engines with worn cylinders. But with the growing availability of new aftermarket engine blocks, engine builders are asking for pistons that will fit standard bore sizes so they don’t have to bore the new blocks to oversize. So piston manufacturers are responding to what their customers are asking for and increasing the availability of standard bore size pistons for the more popular applications.
The performance side of the piston business is really pumping. The growing popularity of GM’s LS1 V8 has created a strong market for pistons to fit various bore sizes, strokes and cylinder head configurations. It’s the same story with late model Ford 4.6L and 4.9L V8s, too. These late model engines are the hot ticket to performance, and engine builders want high compression pistons that will work with longer strokes and aftermarket heads.
There has also been significant growth in the demand for performance pistons to fit popular sport compact engines. Honda and Mitsubishi engines are the ones that are at the forefront of this market, and the people who are serious about racing these pint-sized engines are spending big dollars. In the professional ranks, some sport compact racers are now spending almost as much money on their four cylinder engines as Pro Stock racers who run monster V8s – which is good news for engine builders and piston suppliers.
There is also a growing demand for performance pistons for light truck diesel engines. The popularity of GM’s 6.6L Duramax and Ford’s 6.0L Powerstroke diesel engines in recent years has created a solid market for diesel performance parts including pistons, turbochargers and “tuner” scan tools that allow a user to reprogram the PCM to change the boost pressure, fuel delivery and other variables on the engine.
Piston materials have not changed much in recent years. The basic choices are still cast, hypereutectic and various grades of forgings. SAE 4032 is the most popular piston alloy for street engines, drag engines, naturally aspirated engines and many sportsman class circle track engines, while 2618 is usually the choice for serious racing, marine engines, and boosted and bottlefed engines that produce a lot of heat in the combustion chamber. What has changed in recent years is the design of many performance pistons.
Piston design and manufacturing used to be a relatively low-tech process. Now, with the aid of finite element analysis and other computer modeling techniques, many aftermarket piston manufacturers are using the same tools as original equipment suppliers to create new lightweight super strong designs that can hold up in the most punishing environments. One such design that has emerged is the short skirt “box” or “strut” style piston. The use of reinforcing struts under the piston allows a shorter, stiffer piston that works well with stroker cranks, longer rods and shorter wrist pins. The piston itself may or may not be lighter than a more conventional design piston, but it is certainly stronger.
Another change that’s being made in many performance pistons (and stock ones, too) is to move the ring pack close to the top of the piston. This allows the use of longer rods, which improves the angularity of the engine for more torque. But it also subjects the rings to more heat. This, in turn, requires more durable materials for the top compression ring such as moly coated or nitrited steel or ductile iron, and stronger ring lands (anodized or coated or reinforced with a steel inlay).
Forged pistons have a reputation for being noisier than cast or hypereutectic pistons because they may require greater cylinder clearance. But that isn’t always the case, and some forgings can be run with as little as .004? of clearance in street engines. The key to keeping a piston quiet in a street application is to control its expansion characteristics by carefully designing the piston, and by offsetting the location of the wrist pin up to .040?. Using an offset wrist pin loads the piston against the cylinder wall to reduce rock and rattle when the piston is cold.
Many performance piston suppliers offer a “tool steel” upgrade for piston wrist pins that will be used in high output (over 800 hp) engines. The pins are expensive, but well worth the cost in engines where the ability of the stock pins to hold up may be in question.
Piston coatings are another option that are hot these days. Friction-reducing skirt coatings can reduce noise and protect the piston from galling if the engine overheats or loses lubrication. Friction-reducing coatings applied in the ring lands can also help reduce piston ring and land wear, too. Thermal barrier coatings on the top of the piston that reflect heat are good for applications where the piston may be seared by a short burst of nitrous oxide or high boost pressure from the turbocharger or supercharger. Such a barrier can help protect the top of the piston, but may actually inhibit piston cooling by slowing heat transfer through the piston and rings. For this reason, thermal barrier coatings are usually not recommended for endurance engines like circle track, marine or road racing.
So much for the generalities about what’s new with pistons today. Now let’s hear what the piston suppliers themselves have to say about their newest products and innovations.
Dana Corporation’s Clevite engine parts division does not manufacturer its own pistons, but it does distribute pistons sourced from other suppliers, says Ben Igrison. “One of the biggest trends we see today is the use of coatings that enhance piston durability,” says Igrison. “It adds value to the product and allows suppliers to charge a little more for their pistons.”
He says the diesel piston market has been very strong lately. He attributes that to the high cost of gasoline and the popularity of diesel engines in light trucks. “Diesel engines are hard on the rings. The top ring groove needs armor so it doesn’t pound out. The pistons run hot, and some OEMs such as GM are now using oil cooling inside their pistons to help control heat.” One new diesel application that is creating excitement is the 2.7L five cylinder Dodge Sprinter turbo motor, made by Mercedes for the Dodge cargo van.
Steve Markley says Egge’s market niche is older engine parts that other suppliers no longer carry in stock or have available. “We specialize in older antique engines such as Ford Model A and T, Buick and Packard engines, Dodge four and six cylinder engines, and Chevy four and six cylinder engines. But lately we’re seeing a lot more demand for pistons and other parts for ’50s, ’60s and ’70s vintage vehicles. Our best moving pistons right now are for 429 Cadillacs and 348/409 Chevy V8s. Other applications we’re seeing more movement on are 472/500 Cadillac and 400 Oldsmobile engines.”
“One of the problems with new old stock for older engines is that there was a lot of variation in manufacturing tolerances back when these parts were made. It was good enough for the times, but today most engine builders want tighter tolerances. Egge is remaking many of these older pistons to today’s standards so the parts will continue to be available.”
Markley says Egge only makes cast pistons, no forged or billet pistons. “The pistons are all hand molded and cast, then hand ground and fitted with pins. Our specialty is short runs that nobody else is willing to make.”
The latest news from Federal-Mogul is the availability of the “ThermoshieldTM” ceramic heat reflective coating for piston tops. The new crown coating can withstand combustion temperatures of up to 2,000° F and delivers three times the surface hardness of hard-anodized coatings. The coating is available on their hypereutectic pistons and PowerforgedTM pistons.
The coating is applied through an immersion process using electrical impulses that convert the piston surface into an extremely strong, smooth and heat resistant complex ceramic. Because the Thermoshield barrier is atomically bonded to the piston substrate, the material is highly resistant to flaking and cracking and provides exceptional protection of even sharp corners. The coating is also well suited for the top ring groove to prevent micro-welding.
Jeff Richardson says conventional piston crown coating technologies such as hard anodizing, sprayed ceramics and electroplating produce significantly lower surface hardness than the Thermoshield process and are far less resistant to corrosion, cracking, scratching and wear. The use of piston crown barrier coatings is becoming increasingly popular in many demanding high-temperature applications such as turbocharged and blown engines, and those boosted with nitrous oxide, to reduce detonation.
The new Thermoshield applications include Powerforged pistons for 5.4L Ford Lightning (p/n L2622F), Supercharged 4.6L Ford (p/n L2623F) and 540-cubic inch Chevrolet (p/n LW2633F), and hypereutectic pistons for 5.7L Dodge Hemi (p/n H899CT). Coming soon are coated pistons for GM 4.8L, 5.3L and 6.0L V8, 3.5L V6 and 2.2L GM Ecotec.
In addition to the Thermoshield crown coating, each new Sealed Power and Speed-Pro piston also features Federal-Mogul’s exclusive DuroshieldTM antifriction skirt coating, which helps eliminate scuffing and other skirt and cylinder wall damage in high rpm, high temperature applications.
“Racers are constantly pushing the envelope, trying to reduce weight and friction. Consequently, we’re doing more prototype development work with billet pistons for people who are in the upper levels of racing,” says JE’s Alan Stevenson. “We’ll run FEA (finite element analysis) on a new piston design before we ever cut the first piston. The virtual testing saves us a lot of time and accelerates the development process.”
He says that many top racing teams today have fulltime engineers who create their own unique piston requirements. “They give us a design they want, and we develop the piston and test it. The racing market is so fluid and dynamic that billet pistons are the only way to give our customers what they want on a timely basis.”
Stevenson says 0.8 mm rings are used by more and more high end racers to reduce friction. The rings are expensive, up to $65 each! But many teams believe the cost is worth it. The rings are expensive because they require high purity materials and exact manufacturing tolerances so they will be perfectly flat. The ring grooves in the pistons must also be cut with exacting precision to support the rings.
Gas porting is also a popular trick to improve ring sealing in high revving performance engines. Vertical gas ports on the top of the pistons work well for drag racing, but the ports tend to clog up with carbon after awhile. Lateral (side) gas ports are better for circle track and high output street engines.
JE Pistons currently has a new line of coated pistons that use materials developed by a local aerospace company. The coatings include a thermal barrier crown coating, a “Tuff Skirt” (TM) friction reducing coating for piston skirts, an oil shedding coating for the underside of pistons, and a special anodizing treatment for the wrist pin holes to prevent pin galling under high loads and extreme operating conditions.
“We’ve added over 100 new application numbers this past year,” says Stevenson.” This includes new standard bore pistons for domestic aftermarket engine blocks, new big block Chevy nitrous oxide pistons, new pistons for aftermarket Chevy 23 degree heads and 18 degree Big Chief heads, and new “FSR” forged pistons for sport compact engines including the Nissan 240SX and Skyline.
KEITH BLACK/ SILVOLITE/ UNITED ENGINE & MACHINE
This company has launched several new lines of forged pistons including their “Premium Series” 2618 fully machined performance pistons (150 new applications since last year), and their “FHR” (Forged Head Relief) pistons for street applications (13 new numbers). KB/Silvolite/United’s Scott Sulprizio says the new pistons compliment their claimer budget piston line and hypereutectic piston line.
Sulprizio says his hypereutectic pistons have been very popular with budget racers because the pistons easily last four seasons. They just don’t wear like ordinary cast pistons, he says.
“Our emphasis now is on expanding our line of forged pistons. We have some new Chrysler pistons as well as 10 new pistons for 460 Ford. By mid-summer, we’ll have some new forged pistons for the 4.6L Ford, too,” explains Sulprizio.
Trey McFarland says Mahle is building its inventory in stock pistons to provide more standard bore sizes so engine builders don’t have to bore new aftermarket blocks to oversize.
“We also have a new ‘Gold Series’ forged piston for the Honda H22 engine, which is a very popular engine with sport compact racers. This piston has a special coating so it can be used with a stock aluminum block without having to sleeve the block,” McFarland says.
“Mahle is also getting into diesel performance pistons. Mahle is the largest manufacturer of OEM diesel pistons in the world, so are offering some new performance pistons for light truck applications that feature steel ring grooves,” says McFarland. “We also have some all-steel pistons for high load applications that are limited to 4,500 rpm, but they can handle much higher loads than aluminum forgings. Some diesel racers are now using as much as 100 psi of boost pressure in their turbocharged engines, and the pistons are often the weak link.”
McFarland says Mahle uses a special gray phosphate “Grafoil” coating on its pistons that reduce friction and ring land wear. “Most other manufacturers use a spray on coating that wears off. Ours was developed to meet OEM requirements and can last upwards of 200,000 miles. The coating is also compressible so it conforms to bore irregularities and helps cushion and quiet the pistons.”
New pistons from Probe Industries include a 625 gram hollow dome 13:1 compression piston for 454 big block Chevy engines with .060? oversize bores and various connecting rod lengths and strokes. Also, flat top and reverse dome pistons in several stroke variations for Ford 4-1/8? bore Dart and World aftermarket engine blocks.
For small block Chevy, Probe offers a .030? oversize 351 gram piston with a 118 gram standard wrist pin, a .120? wall 98 gram wrist pin, or a .090? wall 75 gram tool steel wrist pin.
Probe’s line of sport compact pistons include Nissan, Mitsubishi, Subaru and Toyota engines in addition to Honda. Recent additions include a new 87 mm piston for Honda K-series blocks (reverse dome for turbocharged, and flat top for street), and new pistons for stroked Mitsubishi engines. The fastest growing applications in the sport compact segment,” says Chris Huff, “are the Mitsubishi and Subaru turbo engines.”
Another new product of interest to our readers from Probe is their $999 “Piston Machining Fixture.” The fixture allows pistons to be easily mounted for cutting and custom machining.
New from Ross Pistons is a line of diesel performance pistons for Cummins, Powerstroke and DuraMax light truck applications. Ross’s Moe Mills says the new line was introduced at the SEMA show, and also includes performance pistons for John Deere and Caterpillar tractors. These are forged pistons with a special dish design that reduces smoke and maximizes power.
For automotive applications, the company is making all kinds of custom pistons for small block Ford and Chevy V8s that use aftermarket heads and various stroker cranks. “With so many different head and stroke combinations, it’s hard to stock a lot of different piston sizes on the shelf. So we are becoming predominately a custom piston company once again,” says Mills.
Wiseco has just introduced a new line of Chevy LS1 heavy-duty nitrous oxide forged pistons with a “semi-strut” design for engines producing up to 1600 horsepower. The pistons are available in various skirt lengths for stroker cranks, and have been used in a special 500 cubic inch LS1 engine project. The wrist-pins are offset to provide quiet operation, and coatings are available to suit customer’s requirements.
Wiseco’s Brian Nutter says the company coats all of its sport compact pistons, and offer the pistons with a premium nitrited steel ring pack. The pistons are 2618 alloy forgings and cover most of the popular engines.
“The sport compact market has really taken off for us,” says Nutter. “Some Honda racers are using our 204 gram piston that is essentially the same as our IRL (Indy Racing League) piston and costs $650 a set. That’s serious money!”