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Racing Pistons and Rings
The growth in engine displacement has been fueled by several factors: the never-ending quest for more horsepower, and the increased availability and affordability of both OEM performance blocks and aftermarket blocks with larger bores and bore spacing.
By Larry Carley
Cubic inches is the name of the game today. The performance piston market is being driven by bigger bore blocks and stroker crankshafts. A few years ago, a 540 cubic inch motor was a monster motor. Nowadays, some professional drag racers are running engines as large as 850 cubic inches, and 600-plus cubic inch big block motors are common on the street. Even small block V8s have become supersized, with bore and stroke combinations providing upwards of 450 cubic inches of displacement.
The growth in engine displacement has been fueled by several factors: the never-ending quest for more horsepower, and the increased availability and affordability of both OEM performance blocks and aftermarket blocks with larger bores and bore spacing. This, in turn, creates more demand for larger pistons as well a greater variety of piston compression heights and skirt lengths to accommodate different stroke crankshafts.
Another factor driving the performance piston market today is the proliferation of aftermarket cylinder heads. Many of these heads have different valve angles and locations compared to the stock heads they replace. This creates a demand for more “custom” pistons with different dome or dish configurations and different valve reliefs. As time goes, on many of these custom designs have actually become new SKUs on the shelf (or design profiles in the piston manufacturer’s computer) that are available on demand. With CNC machining, pistons can be made-to-order using existing profiles to fit almost any block, cylinder head and crankshaft combination.
The growing popularity of new engines such as the Chevy LS series (LS1, LS2, LS6, LS7, etc.), plus Ford’s modular V8s and the new Chrysler 5.7L and 6.1L Hemi has also created a demand for more new pistons. Take the LS1, for example. General Motors has produced a number of variants of the original bore size, including 3.898˝, a truck block with 4.000˝ bores, the LS2 with 4.001˝, and the LS7 and LSX blocks with 4.125˝ bores. Many of these engines are being built and installed in older cars, including street rods and drag cars. The availability of aftermarket intake manifolds that allow the Chevy LS and modular Ford V8s to be fueled by a carburetor make such engine swaps easy. And for those who want fuel injection, there are aftermarket bolt-on fuel injection systems that simplify installation issues.
Also pushing the envelope on the newer Chevy LS, Ford Modular and Chrysler Hemi engines are bolt-on supercharger kits for street applications. Some of these twin-turbo kits are pushing power outputs to well beyond 1,000 hp (as much as 1,200 to 1,400 hp in some cases!), which demands stronger, more reliable pistons in these motor. Stock pistons can usually handle 400 to 500 hp. But at higher power outputs, stronger forged pistons are a must.
Competition between the piston manufacturers is also driving the development of new piston designs. The short-skirt, box-style piston that features a shorter, lighter wrist pin and narrower rings has become the gold standard today for performance racing pistons. The shorter skirt allows more clearance underneath for a longer stroke crankshaft, and the shorter pin reduces weight.
The increased rigidity of the piston combined with CNC profiling of the piston taper allows many of these pistons to be installed with tighter piston-to-cylinder clearances. Reducing the diameter of the piston at the top where the piston is hottest allows it to handle the heat without expanding too much and scuffing the bore.
To reduce the risk of scuffing, many performance pistons now come standard with an anti-friction side coating. Many of these are applied with a stencil to precisely control the thickness and placement of the coating on the skirt. These coatings are not just a “break-in” coating but a durable coatings that will last the life of the piston.
CHANGES IN RINGS, TOO
Higher combustion temperatures and piston loads combined with rings that are relocated closer to the top of the piston for longer stroke crankshafts means the top rings are running hotter than ever before. Most performance pistons have some type of coating or anodizing treatment in the top ring groove to prevent the ring from welding itself to the piston or pounding out the groove. The top ring, in most cases, must also be steel or ductile iron, and faced or coated with some type of wear-resistant material such as moly, chrome, nitriding, or one of the new “aerospace” vapor disposition or plasma spray coatings.
Racers want thinner rings that generate less tension to reduce friction, so ring dimensions have been shrinking. Many NASCAR and Pro Stock engines are now using compression rings as thin as 0.7 mm, and most Formula One engines are now down to 0.6 mm. These skinny rings produce very little tangential load (about 1.5 pounds), which minimizes friction and allows the rings to conform more easily to any bore distortion. Many of these engines are also using Napier style second rings to keep oil out of the combustion chamber (where it can cause detonation).
Cast iron piston rings remain popular with many budget-minded dirt track claimer motors as well as many street performance and other racing applications. But for higher output engines, ductile iron or steel rings are usually required. Ductile iron rings have roughly twice the tensile strength of gray cast iron, and three times the fatigue strength. Steel rings, by comparison, have almost four times the tensile strength and fatigue strength of gray cast iron. Increases strength reduces the risk of ring breakage and failure. But the trade-off is a higher price.
For high boost turbocharged and supercharged engines, and engines using large doses of nitrous oxide to add horsepower, ductile iron or steel top rings are probably a must. Many racers prefer to use nitrided rings made from steel wire because the rings can handle high loads and thermal shock better than other materials. Nitriding penetrates into the metal and won’t flake off like other surface coatings.
Plain cast iron rings are not recommended for engines that run on alcohol because alcohol cuts lubricity. Some type of coated rings or chrome rings must be used with alcohol.
On engines that have Nicasil(tm) coated cylinder bores or liners, moly or tungsten carbide faced rings work well.
NEW PISTON & RING OFFERINGS
To find out what some of the latest offerings are from aftermarket piston and ring manufacturers, we contacted the following companies for their input both about new products and trends that are affecting their businesses. Here’s what they told us:
Berri Meza of Arias Pistons said his company mainly manufactures custom pistons for a wide variety of applications, including restoration engines, motorcycles, sport compact cars, domestic engines, diesels, even aircraft.
“We offer pistons in just about any bore size imaginable. We have made pistons as small as 1.750 inches in diameter and as large as 6.500 inches in diameter, with bore sizes as large as 7.750 inches being requested!”
Meza said Arias will be introducing a new premium line of lightweight pistons with a strutted design, shorter wrist pins and thin ring pack. The primary market will be European, naturally aspirated engines, with more domestic applications to follow.
“We offer 1.2 mm gas nitrited top rings from 81.0 mm bore to 89.5 mm. These rings are also available for many domestic engine applications, with a 1.2 mm Napier second oil ring and standard oil rings.
“Eighty percent of our business is custom pistons,” said Peter Calvert of CP Pistons. “Our market is the professional racer rather than the Saturday night guy, so we have literally hundreds of piston profiles that can be combined for almost any bore and stroke and cylinder head combination. All of our pistons are 2618 alloy forgings.”
Calvert said the Chevy LS market has really taken off and may eventually replace the Chevy small block as the most popular performance application. “We are doing a lot of pistons for these engines, and also for Ford modular V8s including the 2V, 3V and 4V engines. We supply Saleen with pistons for all of their engines.” Calvert also said the sport compact market has also been huge for his company, with many new pistons being made for Honda, Nissan, Subaru and Toyota engines. “We’re now adding pistons for ATVs and off-road motorcycles.”
The newest product from CP Pistons is a line of gas nitrited rings for sport compact engines. The line will be expanded to cover domestic V8s also. The nitrited rings provide good heat resistance and work well with nickel/carbide hardened blocks.
DEVES PISTON RINGS
Deves is known for its Swedish steel alloy oil control rings, which is a unique 4-piece design that automatically sets and maintains the proper ring tension once the rings are installed. These rings are used primarily in stock engines, and have not been used much in racing. Yet Deves supplies its piston rings to Ferrari, so these rings may be an option for racers.
Nick D’Agostino said Diamond Pistons recently added 20 new part numbers for Chevy LS, Chrysler Hemi and Ford modular V8s. “We have seen a lot of demand for pistons to fit the GM 6.2L L92 engine and the 5.7L Chrysler Hemi. So we now have shelf stock for these two engines.”
As for trends in the piston market, D’Agostine said “Boost is king!” He said many Outlaw 10.5 racers that were traditionally died-in-the-wool nitrous fiends have turned to superchargers and turbochargers to get their power fix. The nitrous racers are still out there, but their numbers are dwindling.
Also, everybody wants bigger and bigger motors these days. Longer stroke crankshafts and bigger bore, taller aftermarket blocks require a shorter compression height on the pistons and makes it more difficult to design a new pistons that will fit the other parts. “This is something we advise our customers about constantly. All parts need to be considered before a single one is ordered. The engine builder has to make sure that everything will work together.”
DSS Racing builds a variety of Ford stroker crate engines, including pushrod and modular overhead cam engines. Tom Naegele said that Ford is coming out with a new big bore BOSS block, so they will have a full line of pistons for this block as well as Ford big bore blocks from Dart and World Products.
Naegele said DSS also has a new line of SX forged pistons that are an “economy” piston with features not usually found in pistons in this price range. They are available with a flat top or dish design, generous valve reliefs, an advanced CNC skirt profile that allows tighter clearances, and forced oilers for the full floating wrist pins. The pistons are also about 100 grams lighter than a stock piston. The SX pistons are available for SB Chevy and Ford stock and stroker engines.
The next step up is the Extreme X piston line, which is even lighter (about 160 grams lighter than a stock piston) and designed for high output nitrous, supercharged and turbocharged SB Ford and Chevy stroker motors. The pistons have fully CNC machined tops, sides and bottoms, and are available with tapered wrist pins.
DSS also does custom pistons, mostly for drag racing. “These are the XR Series, which are in some of the fastest drag cars in the world,” said Naegele. “The trend today is toward 1,000-plus hp small blocks, so we design pistons that can handle this level of power.”
“I can’t believe the flathead market is still going as strong as it is,” said Steve Markley of Egge Machine. “We’ve redesigned our big bore flathead Ford piston with a shorter skirt and flattened dome for three different strokes: 3-3/4˝, 4˝ and 4-1/8˝.”
Egge specializes in hard-to-get parts for older, “obsolete” engine applications, including cast pistons for 283 and 327 Chevys, 348 and 409 Chevys, 400 Oldsmobiles, 389 and 400 Pontiacs, 472 and 500 Cadillacs, 455 Buicks, 273 Plymouths and more. Most of these are hand-cast pistons, though some forgings are available. The cast pistons are designed primarily for restoration and are not really racing pistons (though they can handle moderate increases in power).
FEDERAL MOGUL/SPEED PRO
Scott Gabrielson said Federal Mogul’s Speed Pro product line is targeted at the street performance customer and the Saturday night racer rather than the high end professional racer. “We have forged pistons to replace the stock pistons in Chevy LS1 and LS2 engines, and also pistons for stroker motors, including new ones for 540 cubic inch big block Chevy applications. We also make forged pistons for the Ford Lightning and Mustang Cobra, and hypereutectic pistons for Ford modular motors and the new Chrysler Hemi.”
Speed Pro pistons have a DURASHIELD (TM) anti-friction skirt coating to eliminate scuffing and other skirt and cylinder wall damage in high rpm, high temperature applications. The pistons also have a THERMOSHIELD (TM) heat reflective ceramic coating on the piston crown and top ring groove. The crown coating can withstand combustion temperatures of up to 2,000° F and provides three times the surface hardness of hard-anodized coatings. 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. The coating bonds to the piston substrate, so it won’t flake off or crack.
Gabrielson said Federal Mogul is currently designing a new line of performance pistons with shorter pins and skirts that should be available later this year.
As for rings, the move is to thinner, lower tension rings, though 1.5 compression rings and 3.0 mm oil rings remain the most common. Most of Speed Pro’s top rings are now made of ductile iron with a plasma facing. For higher horsepower applications including Pro stock and Top Fuel racing, Hellfire rings made of a special tempered ductile iron are available from Speed Pro.
Federal Mogul also has a new high tech ring coating called Goetze Diamond Coating (GDC) that will be finding more new applications. It is a nano-diamond dispersion coating that improves durability, wear and scuff resistance far beyond all existing chrome-ceramic coatings. The coat is now being used on OEM rings in a number of European diesel, heavy-duty, mid-range and automotive engines.
HASTINGS PISTON RINGS
Hastings is currently developing a new ring line for racers that will be available later this year, said Jeffrey Guenther. He couldn’t say much about the new rings now, but said they would probably have some type of advanced coating to reduce friction and wear.
To date, Hastings has used mostly moly and PVD coatings on high performance rings. “Nitriding works well with hard nickel/carbide hardened cylinder bores or liners, and we’ve done a few of those. But our focus now is on developing new types of coatings for specific applications.
Guenther said that ring selection is key to engine durability. “Cast iron rings are okay up to about one horsepower per cubic inch. For higher power levels you need ductile iron or steel. Steel is strong and can be made very thin, and works in engines that produce 2 or more horsepower per cubic inch. But steel is expensive and requires high quality alloys. In nitrous engines, chrome ring facings work better than moly, which tends to flake.”
JE Pistons has just launched their new SRP Professional series of lightweight racing pistons. The pistons has forged side relief (FSR) forgings, and precision CNC machined ring grooves and skirts. The pistons also come with JE Pro Seal rings (1.2 mm steel top ring, 1.5 mm Napier style second ring, and 3.0 mm oil ring).
Alan Stevenson said the new line of forged pistons, which are made in the USA, are 50 to 60 grams lighter on average that most other forged pistons. The pistons were designed using computer finite element analysis software to optimize strength and weight. Billet prototypes were then CNC machined for testing to verify piston durability and performance. Production pistons are made of high silicone 4032 alloy for reduced piston-to-wall clearance. The wrist pins are also about half an inch shorter to minimize weight.
Applications for the new SRP pistons include Chevy LS2, LS3 and LS5, 350 and 400 SB Chevy, and 4.6 and 5.4L modular Ford 2V engines. Pistons are available with a flat top, or inverted or regular dome.
KEITH BLACK PISTONS
Scott Sulprizio said Keith Black has introduced new a number of new lightweight pistons including ones for SB Chevy 305, Chevy LS1, Ford modular V8, and a 4-1/2˝ piston for Chrysler big blocks.
“We are moving toward pistons with shorter wrist pins and skirts in our premium forged line. We have also expanded our FHR series 4230 alloy street forged piston line with 18 new part numbers for Chevy and Pontiac applications.
“We have pretty good coverage in our hypereutectic piston line, so we have not expanded that line much recently, but we are doing some custom pistons.”
“One of the fastest growing applications for us is the Chevy LS1,” said Trey McFarland of Mahle. “There’s a lot of interest in big displacement small blocks, up to 489 cubic inches in some cases, so we are looking at pistons for all of these combinations.”
McFarland said Mahle is also doing pistons for Honda and Toyota aluminum blocks. “The Gold Series pistons have a special skirt coating that allow an aluminum piston to run in an aluminum bore without galling. The OEM cast pistons have iron filings in them for bore computability, so if an engine builder wants a stronger forged piston for one of these applications without having to install iron sleeves in the block, they can use one of our forgings with the special coating.”
“Our pistons have a slipper skirt design with shorter wrist pins to reduce weight and drag. The pistons are designed in such a way they they don’t really need extra box webbing and can handle 1,200-plus hp in a V8 engine. The pistons have a phosphate dry film coating that protects the ring grooves and pin bores.”
McFarland said Mahle also applies a proprietary coating to the piston skirt that not only protects against scuffing but also helps the piston run quieter. The graphite coating has a phenolic carrier and is screen printed on the sides of the piston. The coating is compressible and has cushioning properties to help dampen the piston as it crosses top dead center so the engine runs quieter. The coating is quite durable and can last up to 200,000 miles or more in a stock engine.
“Mahle does some custom pistons, but they are a full feature design, not just a remachining of the valve reliefs or a change in compression height. Most of these are gas ported pistons for cup teams or endurance racing,” said McFarland.
PERFECT CIRCLE PISTON RINGS
Perfect Circle has not added any new rings since Mahle bought the division from Dana/Clevite. But Perfect Circle is still heavily involved with producing ring sets for NASCAR race teams, and is also doing more rings for NHRA drag racing Pro Stock teams.
“Rings are getting smaller in both NASCAR and Pro Stock drag racing, but not Top Fuel,” said Tod Richards of Perfect Circle. “The smaller rings seal better at high rpm. Many of the teams are using a more exotic ring design such as a one-piece oil ring instead of a more traditional three-piece oil ring. The are also using steel rings with proprietary facings.”
For the weekend racer, Perfect Circle recommends plasma moly steel rings. These rings also hold up well for circle track applications. For nitrous, supercharged or turbocharged engines, their PC479 firepower rings are the best choice.
Like other piston and ring manufacturers, Richards said Perfect Circle is getting requests for rings to fit larger and larger bore diameters. There’s not a lot of them yet, maybe fewer than a hundred, who are running bores of 5˝ or larger. But their numbers are growing. It’s hard to justify the tooling cost to produce rings with a limited demand. But as the numbers grow, the economics can change.
Richards said the demand for Chevy LS rings is up sharply, but those for Ford modular engines has been relatively flat in comparison. A lot of that has to due with racing rules. The LS engine is a spec engine in some levels of NASCAR, which has helped create a market for parts for that engine.
Probe has a number of new pistons applications including pistons for supercharged BB Chevy, pistons for 4 inch and larger bore Chevy LS series engines with various valve reliefs, new pistons for 400 and 455 stroker Pontiac engines with up to 4-1/2˝ stroke, new lightweight pistons for stock and stroked SB Ford engines, new pistons for Ford 3V modular engines, new pistons for BB Ford Super Cobra head engines, and pistons for stroker Ford FE 390 and 428 engines.
John Mendenhall said Probe has also been busy expanding its offerings for sport compact applications, including Toyota Supra, Nissan and Mitsubishi engines.
Probe uses 2618 alloy for all of their forgings, and offers coatings as an option. Mendenhall said Probe currently has over 800 part numbers on the shelf, which means racers can often find they piston they need without having to order a custom piston (which Probe also makes).
“The trends we are seeing are more demand for Chevy LS pistons, more pistons for stroker FE Ford engines as well as Ford Cleveland engines.”
Ross Pistons recently introduced a new line of BB Ford pistons for stroked and overbored engines, and will be introducing a new line of forged Chevy LS7 pistons to fit bore sizes up to 4.200˝ later this year.
“Probably 80 percent of our business is custom work,” said Chris Madsen of Ross Pistons. “Big motors are back, with 800-plus cubic inches and 5.4˝ bore spacings. It won’t be long before we see 1000 cubic inch engines.
“The LS1 is very much in demand,” continues Madsen, “but we are also getting a lot of calls for pistons to fit the new Chrysler Hemi. People are installing centrifugal superchargers on these engines so there’s a need to replace the OEM pistons with something stronger.”
TOTAL SEAL PISTON RINGS
“The trend toward longer strokers and higher horsepower levels is putting more demands then ever on the rings,” said Keigh Jones of Total Seal. “Shorter piston heights mean less space between the rings, so thinner rings are more common. Some compression rings are as thin as 0.6 mm, but most are around 1.0 mm.”
Jones said a lot of aerospace type coatings are now being used on rings, including materials that were not available to racers a few years ago. “PVD (plasma vapor deposition) coatings work better than nitriding, and produce less friction, scuffing and wear.”
The bigger aftermarket blocks are really driving the demand for larger diameter pistons and ring sets, said Jones. Some racing rules limit engine displacement, but the general trend is to bigger and bigger engines. Eight hundred cubic inch blocks are the norm in Pro Stock drag racing these days, and 600 cubic inch blocks are not that unusual on the street.
“Our fastest growing product line is our domestic racing piston line. Everybody wants a piston for the Chevy LS1, which we offer in a variety of configurations. We offset the LS1 wrist pin so the engine runs quieter, and put a hard coating on the skirt to reduce friction,” said John Levis of Wiseco Pistons.
“Our newest product is our GFX ring pack that features a stainless steel nitrided top ring, a Napier style second ring, and a 3.0 mm three-piece oil ring with nitrited rails. These are good for oval track and drag racing, and are available with our domestic and sport compact piston lines.
“For the first time, we will also be offering rotating assemblies that include the crankshaft, rods and pistons in one kit. We have partnered with K1 Technologies to make these kits possible, and will offer kits for SB and BB Chevy, SB Ford, Chrysler Hemi and various sport compact cars.”
Levis said that about 30 percent of Wiseco’s business is custom pistons. They make their own forgings in-house, and can CNC machine the forgings to fit a wide variety of applications.
“In our Pro True Sportsman line, we’re offering new combinations for BB Chevy to fit 4.00˝ to 4.750˝ stroke cranks, and compression ratios from 10:1 to 12:1.”
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