piston related info


Staff member

If your looking for new pistons do some research, youll need to know the bore size, stroke, rod length, piston pin type,piston ring design , and at least a general idea on combustion chamber and valve size, valve diameter, and intended valve lift and cam timing to get clearances correct.and several other related facts before you can select the correct piston
lets look at your options, obviously both your intended use and/or rpm range will effect the logical options as will your budget.
your first option is between cast, hypereutectic and forged alloy pistons, cast are generally cheap and function well under low heat and load like normal driving, hypereutectic have a much stiffer alloy that
has silicone added and these are slightly stronger, forged are significantly stronger , less likely to break,but more expensive
your second common choice is selecting between 5.7" and 6" connecting rods.
your third choice is between pressed and full float wrist pins.
your fourth choice will depend on compression ration desired.

examples, of cast and hyper pistons for a common 350-383 sbc, usually cost about $170-$250 per set of 8
forged will commonly run in the $370-$500 range per set but will be a better option if nitrous is used or you intend to run over 4000 feet per minute in piston speed frequently
(that way you can self assemble the piston on each connecting rod)
(which comes in handy when you need to change piston deck height/quench, and side clearance etc.)
(which allow a true custom fit)
and if possible forged pistons
(which are more durable and less subject to as rapidly occurring damage from detonation)
now I have zero problem using hyper-eutectic pistons in the proper applications because they work as well or at least as well as required with little or no down side if you remember the previous stated limitations

related info












http://www.kb-silvolite.com/assets/auto ... ctions.pdf

http://www.hotrod.com/techarticles/engi ... index.html

http://www.circletrack.com/techarticles ... index.html







http://www.enginebuildermag.com/Article ... s_new.aspx






http://www.circletrack.com/techarticles ... index.html


http://www.techlinecoatings.com/article ... rticle.htm

http://www.kb-silvolite.com/article.php ... ad&A_id=64



read these links


http://www.hotrod.com/techarticles/stee ... index.html

here is where you, or your machine shop can screw things up on ring to bore seal, you need to have the cylinders bored and honed to the correct size specified by the manufacturer of the pistons,after MEASURING THE PISTONS to verify their size per the piston manufacturers instructions, then gap the rings per the ring manufacturers instructions, when you hone the bores,get and use block deck hone plates, during the hone process , keep in kind you want to use the same (STUDS OR BOLTS) the machine shop used and the same torque settings they used when the cylinders were honed with deck plates or the distortion of the bore and ring seal won,t be identical (exactly round)or ideal, keep in mind the piston side clearance must match what the piston manufacturer states.
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Staff member
heres a quote from keith black pistons, concerning piston alloys


Which alloy is strongest? Answer, it doesn't matter. All piston alloys used by the industry today are strong enough, including cast iron. The real story is in more technical terms like fatigue strength, thermal conductivity, wear resistance, expansion rate, coefficient of friction and specific gravity.

Thermal conductivity is probably the least understood of all terms as it applies to a piston running in an engine. The effective conductivity of a piston (not the alloy) can be altered with coatings, surface area, section design, polish, and top land design. Ideally, the combustion surface of a piston would run at a little over 500°f and not exceed 600°f. The 600°f not-exceed temperature is the most important when it comes to engine life because a 600°f piston top can ignite the fuel mix independent of the spark plug.

Our performance is that we will make higher Hp and better low RPM torque with the best economy and smog numbers. It also suggests that we will have to maximize design efforts to cool the piston to keep the piston top below 600°f. On the opposite end of the spectrum regarding thermal conductivity is our forging alloy 2618. It is the most conductive alloy used by anyone making performance pistons. When the top gets hot the whole piston gets hot and expands accordingly. Noisy when cold and just fine when warmed up. The relatively cold piston top does hurt low RPM power and economy some, but design features can offset some of the shortcomings. Some forgings have been made with a slot at the oil drain back area for the purpose of restricting heat flow to the skirt. The design works and allows forgings to run almost as tight as hypereutectic pistons. Unfortunately, the heat slot weakens the piston below what is required for modern high Hp engines.

The coefficient of friction of all materials is pretty much the same when lubricated as the oil really determines how much slip you have. The unlubricated condition is the important number, especially since it is closely tied to wear and gauling. An engine seeing detonation tends to burn the oil off the cylinder walls. The surface finish on all KB Pistons is designed to put the oil back, but severe detonation can produce a situation with a dry cylinder and a tight piston. The hypereutectic alloys, those with at least 16% silicon (4% free particulate), have a structure somewhat similar to fiberglass. This hypereutectic alloy will slide on the free silicon when oil is not present. This phenomenon is what is responsible for the almost never-gaul never-wear reputation of KB Hypereutectic Pistons.

Specific gravity of piston alloys does affect the weight. Keith Black did make some magnesium pistons that worked. For the most part, though, most lightweight materials tried as piston material fall from thermal conductivity, wear, or fabrication problems. Currently the big savings in weight comes from design changes and the use of real long connecting rods.

Expansion rate varies from aluminum alloy to aluminum alloy with about a 15% total spread. Our forged pistons expand about 13% more than our hypereutectic. Big deal! 15% of 2/1000's of an inch is only .0003". Twice, nothing is still nothing. Why can't we run .002" clearance on performance forgings? The expansion of a piston is controlled by two factors, coefficient of thermal expansion and temperature. The expansion rate is the small player, but the temperature is drastically affected by the thermal conductivity of the piston. All successful forging alloys send combustion chamber heat to the piston skirt quickly, and hot skirts require the extra skirt clearance.

Strength and ductility are often confused terms. Most all pistons are more than strong enough at room temperature, with a slight edge going to the forging alloys. At high temperature the hypereutectic alloy has the edge strength-wise. The problem is if your pistons are 800°f and strong the engine is hypereutectic alloy is a slow conductor of heat. The benefit in in detonation mode and will continue to escalate temperature to destruction. (Direct injection engines may allow higher piston top tempertures.) Ductility is the main area where forging alloys really win. Short of breaking a wrist pin, forgings usually stay attached to the connecting rod even with nuts, bolts, and valve heads sharing the same combustion chamber space. A dropped valve on a forging is more likely to stick in the piston and limit damage to the cyliner head, rod, and piston.

In summary, we make forged 2618 and 18% hypereutectic pistons to hopefully offer the best piston choice to the end user. The hyper pistons have been designed to run forever and are a little more high tech. The forgings are safe. They are excellent when used in development type engines and some very high heat engines. Top fuel and 5 Hp/cubic inch plus engines see a lot of heat, and it is a little easier to cool a forged piston top. Hypereutectic pistons are a little less likely to form cracks than forgings because the alloy structure is somewhat like fiberglass. Cracks occur from flexing. The KB Hyper Pistons are designed not to flex. If the engine builder leaves a rod bolt in the intake, this soon becomes a component flex test. There are no winners ... and piston, cylinder, and cylinder head are usually proven not very flexible.

John Erb
Chief Engineer
KB Performance Pistons


Staff member
info thats well worth reading thru
http://www.hotrod.com/techarticles/hrdp ... index.html

http://www.mustangmonthly.com/techartic ... index.html

http://www.rosspistons.thinkhost.com/re ... LATION.pdf

http://www.jepistons.com/dept/tech/dl/p ... rc4032.pdf

http://www.jepistons.com/dept/tech/dl/p ... rc2618.pdf


Piston Alloy Comparison
4032........................... ................................2618
High silicon ......................................... ...........No silicon
Low expansion ................................... .........High expansion
Tighter piston-to-wall clearance . ...........More Piston-to-wall clearance needed
Quiet Operation .................................Noise when cold
Less ductile ........................................... More ductile
More stable & consistent.................... ...... Higher resistance to detonation
Longer life cycle.............................................. Shorter life cycles
Harder .................................................... ........Softer

Now IVE used HYPEREUTECTIC, and both common forged alloys
The experiences I’ve had seem to be that hypereutectic pistons work great up to the point you get into detonation, and then they fail rapidly and catastrophically, if subjected to the head and pressure, coming apart in chunks.
The forged pistons in either alloy will sustain a great deal more abuse without showing it for much longer but ANY piston subjected to detonation will eventually be destroyed.
Hypers are almost BRITTLE, in comparison, and while bouncing a valve of any piston is a very bad idea, the forged pistons are usually scared, and nicked if the impacts minor, hypers can break apart. Leading to much larger problems than a simple bent valve.

AND you will eventually float valves or run into detonation with any engine your racing and pushing for every last bit of hp. or alloying the engine to run a bit lean at some point, especially with nitrous, or a supercharger.
So if your building a serious combo Id suggest thinking seriously about forged pistons but as the manufacturer for the correct clearances and part numbers and carefully follow the installation instructions.

when ever you order parts like pistons that must be fitted precisely to a block,ok the first factor you need to know is the TRUE bore diam. of the block, and if its consistent between all cylinders, youll also need to know the deck height on the block, the connecting rod type, IE, is it set up for pressed or floating pin pistons and if the block ,decks parallel and square to the crank center line, you'll need to order pistons that fit the bore or in most cases you order pistons a bit larger than the current bore size and have your engine builder bore, hone and fit the pistons to your block with the correct side clearance, and order a matching ring set.
the cylinder heads combustion chamber shape , you chose to work with and location in the cylinder heads of that combustion chamber will determine BOTH the dome or dish size, the pistons require to function correctly and the valve clearance you need, along with the cam you select and the way you degree it in to the engine.
remember different piston materials expand at different rates and require different side clearance and ring gaps.(don,t forget that different rings will require a different surface Finnish on the bore surface)

as a general rule HYPER-EUTECTIC pistons will require a tighter bore clearance and more ring gap clearance than forged pistons as they tend to run hotter and expand less in the bore, but you MUST use the manufacturers suggested clearance requirements.
not all piston domes are located to clear all spark plugs, valve sizes or combustion chamber shapes, so ask both the piston and head manufacturers for info they might have on potential problems, most engine builder will know how to correct MINOR mis-matches,
but ordering the correct piston machined for the intended application, and carefully measuring components before and during assembly and NEVER taking ANYTHING FOR GRANTED goes a long way toward preventing problems.
factors like the piston pin length and diam. and the piston pin bore thru the piston, the method of locking the piston to the rod and the heat and rpm band your likely to run those pistons under will require some careful thought if you expect the engine to live a long life, surface finish, heat barrier coatings will also effect the choices.
AS LOTS of QUESTIONS before ordering and carefully check clearances during the assembly process.

Youll also want to keep in mind that swapping too new pistons will generally require re-balancing the rotating assembly


a ball hone with 320 grit used sparingly produces a very good surface finish for moly rings to seal with but a ball hone follows the cylinder wall surface even if its a bit egg shaped or hourglass or cone shaped so its NOT going to be ideal in a well worn cylinder because the rings will not be able to fully contact a non-cylindrical cylinder wall.




use of a deck plate allows the head bolts to be torqued ,this duplicates the stress the heads when installed exert on the block and allows a much better ring seal
http://www.circletrack.com/enginetech/c ... for_speed/
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Staff member
piston speeds over 4000fpm, tend to be a long term durability issue. over 4500fpm generally ARE getting into excessive stress levels



http://www.theoldone.com/articles/engin ... nfacts.htm



Custom Pistons 101: Everything You Need to Know!
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JE Pistons

Why Custom?
JE Pistons stocks thousands of pistons in what is called the shelf stock program; each of which has been built for a high-volume application, such as those pistons built for a traditional small-block Chevrolet engines. Many of the applications where shelf-stock pistons are traditionally used can actually share the same forgings, as the bore dimensions across some of these applications are very similar, as are the build requirements of the piston when it is complete.

Many times, a simple $5 change can help get you what you need. Click here to learn more about $5 changes.

But when you’re building an engine that’s slightly off the beaten path, a custom piston is just what the doctor ordered. A custom piston order form is required for custom pistons but if there’s a reference engine application, you don’t have to fill out every line.

Custom Piston Options Include:

  • Ultra Crown Domes & Inverted Domes
  • 3D Under Crown Milling
  • Vertical & Lateral Gas Ports
  • Ultra Groove
  • Weight Reduction Options
  • Contact Reduction Grooves
  • Accumulator Grooves
  • Double Pin Oilers
  • Pin Fitting
  • Oil Squirt Notch
  • Bottom Oilers for High RPM/severe duty applications


JE offers full under-crown milling to remove as much weight from pistons as possible.
Forged? Or Billet? Which Is Best For Me?
Over the last 70-plus years, the JE Pistons design team has seen just about any engine combination which can be dreamed up and can likely support your engine build with a piston forging to satisfy the parameters required.

A forged piston begins with a mechanical process which requires many hundreds of tons of pressure, whereupon a piston blank – which is shaped somewhat like a hockey puck – is preheated, then smashed into a rough shape which, then cooled and set aside until it is needed for a customer (unless it is a shelf stock part number). There are many steps to the machining process, but a quick rundown has piston blank going through the forging process, then to heat-treating, then into the end-to-end machining following a trail where several steps all come together to produce a ready-to-run, fully CNC-machined piston at the end of the line.


Custom pistons are machined from our wide selection of forgings. However, if a suitable forging is not available, a forged billet can be utilized.
However, there are instances where there is not a piston forging available to work with a particular engine combination, and that’s where billet pistons come into the picture. For instance, when a race team is working with an engine program that has been specifically tailored to their needs, a billet piston may make the most sense for that particular usage scenario. Many of those teams are constantly refining their engine programs and testing various configurations to develop the most efficient burn cycle and flame front.

Want to learn more about piston technology? Head over to the JE Blog!

“The main advantages to choosing a billet over a forging are: first, you don’t need to have a large quantity of parts to justify the cost of making a new forging die and second, any changes to the billet design can be made quickly compared to making a new forging die. No one would consider spending the thousands of dollars required to make a forging die to only make a few pistons. The billet process also allows us to test out potential forging designs before spending the money for a new forging die. Using billets, we can manufacture the pistons and test them out in real world conditions before committing to the cost of making the new forging die,” says Eugene Henson, JE Pistons’ Manufacturing Engineering Manager.


Bead blasting of the underside of billet pistons can help to remove sharp edges which can become stress risers.
Shaping a Billet
In terms of construction, a billet piston starts out as a heat-treated puck, similar in shape to a hockey puck. But unlike a forging, all of the material in a billet piston that doesn’t end up as part of the finished billet must be removed from the puck. This requires a bit more engineering time to design the billet properly, and time from the CNC programming team to create accurate toolpaths to machine the puck into its final configuration.



JE’s advanced CNC machines and cylinder head scanning capabilities allow them to create precise, 3D piston domes.

“If you are developing a racing program you can make slight changes to the strut angles, valve pocket locations, and virtually any part of the structure as you see fit. When working with a forging you are constrained to what the forging you start with can handle. If your engine needs a strut with a more diverging angle than the forging supports, the billet can be just quickly designed to accommodate,” says JE’s Global Automotive Product Manager, Nickolaus DiBlasi.

Available Piston Coatings

  • Top Groove Hard Anodize
  • Skirt Coating
  • Electroless Nickel
  • Thermal Barrier Crown
  • KoolKote
  • Tuff Skirt
  • Oil Shed Coating

This piston has been treated to gas porting, 3D crown design, and has also had precision “ultra-groove” ring lands machined.
Ordering a set of custom pistons is as simple as providing the measurements you require for your application. For more information, please visit www.jepistons.com


What Makes a Racing Piston?
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That clearly is an open-ended question because the answer will single out the uber-sophisticated pistons designed for Formula 1 and World Endurance Challenge (WEC), yet to be completely literal the response must acknowledge hand-modified cast factory pistons used in Hobby Stock racing at the local dirt track.

For the sake of argument, let’s define a racing piston as one that works best for any builder assembling an engine for motorsports competition. From there the discussion can move toward more specific talking points.

“Typically [a racing piston] is a highly developed design that has undergone many iterations to optimize its use under a very specific set of conditions,” said Alan Stevenson, senior technical account manager.

A simple comparison of pistons from the muscle car era of the ‘60s to today’s more advanced products will certainly validate that position. Manufacturers have improved materials and designs through advanced computer modeling to improve power and increase fuel efficiency.

To start this bench racing session, consider the basics of aluminum piston construction. Unless there’s a specific rules restriction, a forged piston will always be preferred in racing over a cast. “Forged is the standard, offering excellent design flexibility and the best cost-to-performance ratio,” said Stevenson. “Cast has no flexibility and can therefore not be developed or optimized. Cast pistons are also heavy and brittle, but they’re cheap to produce.”


Forged pistons can be made of either a forged blank (right), where the entire shape of the piston is machined out of a billet aluminum cylinder, or created from a net forging that is squished closer to its final shape via a forging die (left).
Low-power engines can survive with cast pistons since they won’t see the abuse of blistering heat or high RPM. There’s not much you can do to improve performance with a cast piston, other than grind out a little metal in the crown to clear the valves if a more aggressive camshaft is installed.

In the ‘80s and ‘90s, hypereutectic became a big buzzword in the piston industry. A hypereutectic piston is one that has greater than 12.5 percent silicon in its metal composition, usually around 16 to 18 percent. A standard cast aluminum piston has around 8-to-10 percent silicone content, which improves the hardness and helps reduce wear around the ring grooves, skirt and pin boss. The hypereutectic piston is still manufactured through casting but the alloy is a little lighter, and due to the improved strength the casting can be machined a little thinner to cut down even more weight.

Still, a forged piston will be much stronger and that’s why it dominates the performance market. There are two aluminum alloys popular with forgings: SAE 4032 and SAE 2618. Here’s where another choice is made that often distinguishes, or at least makes a good argument, for a racing piston—although one alloy isn’t always “better” than the other.

“The term ‘better’ is tricky. If only one alloy were better at achieving every goal, there wouldn’t be multiple offerings,” explains Stevenson. “4032 expands less so it requires less cold clearance which tends to run quieter. This could be important for EFI engines with knock sensors. 4032 is less dense so a given design would be lighter than 2618, however 4032 doesn’t have the high-heat annealing resistance that 2618 does.”

Again, silicon content is the differentiating factor. A 4032 piston has about 11 to 13 percent silicon while 2618 has less than .25 percent. “2618 has higher ultimate strength, better annealing resistance at elevated temperatures and has better ductility. In a racing environment, the goal is often to minimize weight without sacrificing durability in high-heat environments. For these reasons 2618 often gets the nod,” continues Stevenson.


The piston on the right uses a 5/64in ring pack. This is a very common size used during the muscle car ere. The piston on the left uses a much thinner 1.00mm top ring. This reduces friction, freeing up horsepower and allowing the engine to rev quicker.
While a majority of racing pistons are made from 2618 aluminum, there are some exotic materials used in high-end racing—or at least they were tried before being banned. Aluminum beryllium alloy, which is exceptionally light and strong with superior thermal properties, was developed by Mercedes/Ilmor for the McLaren Formula 1 team in the late ‘90s. However, the alloy was quickly banned because beryllium dust is extremely hazardous, and in a fire the element will turn into beryllium oxide, which is extremely toxic.

The latest advanced alloy to draw banishment in motorsports is aluminum metal matrix composite, or MMC. Another very stiff, lightweight alloy, MMC is also banned by Formula 1 but continues to draw interest in other areas of motorsports where the rules are more open.

For many years, top engine builders have preferred billet pistons over forged versions—and probably not for the reason you might think. “Billet is not just a simple option to a forging,” said Stevenson. “Billets are approached as complete engineered solutions that are put through several architecture design iterations using FEA modeling to optimize design to a very specific set of environmental conditions. Most popular configurations are offered as a catalog item, but if a combination comes up that doesn’t match, that’s where a forged custom piston can be designed and manufactured at in just a couple of weeks. This is half our business.”

In other words, billet pistons are primarily used in tight-timeline development projects where critical changes can be made quickly without worrying that a proper forging isn’t available. The debate over billet vs. forged in terms of strength will have protractors and detractors on both sides, but generally speaking, a properly executed forging will have inherent strengths in grain structure that a billet piston will not. “Probably 98 percent of racing formulae have a forged option available in the aftermarket,” confirms Stevenson.



Anti-detonation grooves (arrow) are designed to help reduce pressure spikes while contact reduction grooves (just below the crown) reduce how much of the piston’s crown surface make contact with the cylinder wall.
In addition to improved materials and advanced construction methods, specific features have been developed to boost horsepower through either thermal dynamics, reduced weight or reduced friction. Following are some examples of design elements often unique to racing pistons:

Thinner ring packages
Although some exotic engines run 2-ring packages, the majority of racing applications stick with the tried-and-true 3-ring setups. What has changed dramatically is the thickness of those rings, especially in Pro Stock and other non-endurance engines. “You reduce friction and mass, freeing up power and allowing the engine to accelerate faster. The secret to power in any N/A engine is to use the thinnest rings possible, lapped flat and matched with a super-flat ring groove, and ensure minimal axial and radial clearance,” adds Stevenson.

Anti-Detonation Grooves, Constant-Pressure Groove and Accumulator Groove

“Accumulator grooves work on every piston, but work best on gas-ported pistons,” explains Stevenson. “They work according to Boyle’s law; pressure and volume are inversely proportional. Through normal secondary motion (piston rock), the top ring tends to become momentarily unsettled as it rapidly changes direction through TDC. As this occurs near peak firing, combustion pressure tends to make its way past the top ring until it re-settles. Combustion pressure also gets through at the end gap of the ring. Accumulator grooves nearly double the volume below the top ring, reducing pressure according to Boyle’s law and preventing the top ring from becoming pressurized from the underside, which promotes ring flutter.”

Smaller, Lighter Wrist PinsLess weight is always desirable but using a smaller or thinner wrist pin may compromise strength and engine durability. “This often comes at a cost of using better, more expensive materials but also reduces mass to help the engine accelerate faster,” adds Stevenson.


Shortening the piston skirt is a good place to remove mass, but also can be mandatory in stroker applications. Racing pistons can also have different skirt profiles to help them stay stable in the bore at high rpm.
Shorter Skirts
Again, more design changes to reduce weight and friction but these efforts are usually dictated and restricted by the engine architecture, such as length of the cylinder sleeves and the stroke. “The gauge point of the piston skirt must remain captured in the bore at BDC,” said Stevenson.

Thermal Coatings
Some engine builders want to reflect the heat away from the piston, preferring that the valves and cylinder head dissipate the heat to the coolant instead of the pistons and rings through the cylinder wall. Thermal coatings are designed to repel heat from the piston crown, and in some cases the combustion chamber as best as possible.

Skirt Coating
“By far the most friction in an engine is from the rings. A distant second are the bearings. Skirts have minimal friction since they ride on an oil film,” says Stevenson. On racing pistons, top teams use coatings as an insurance policy against overheating. In OEM and daily driver conditions, they are used to protect against dry starts and other situations where oil on the cylinder wall is limited.


This piston features vertical gas porting which allows combustion pressure to get behind the piston ring, forcing it into the cylinder wall and increasing ring seal. It is most commonly used in drag racing applications.
Application Specific Modifications
“Some modifications are inappropriate for one type of racing while done routinely on pistons made for other types of racing,” cautions Stevenson. “Some examples are spinning the bosses, plunging the bosses, drilling holes in the skirts or struts, and 3D under-crown milling.”
3D profiling is a precise milling procedure where the piston crown maintains the same thickness regardless of the dome profile. This step ensures that the crown has the necessary strength and heat resistance for competition with the least amount of weight. “This is especially important when trying to maximize compression ratio, and it can also be used around valve reliefs to promote smoother flame travel,” adds Stevenson.

The actual crown design and valve relief dimensions will be dictated by the combustion chamber and valve geometry. Another racing piston cue is that the engine builder will send a mold of the combustion chamber to the piston manufacturer so that the dome design exactly follows the profile of the chamber.
Finally, some engine builders call for very slight adjustments in the overall piston shape and dimensions to suit their needs.

“Skirt cam/barrel shapes and ring-land diameters are part of the black art of optimizing a design during a development program,” says Stevenson.
As you can see, a racing piston may have one or many of the features and modifications mentioned. The key is designing a piston that meets the needs of the engine builder assembling an engine for a specific competition.

This article was sponsored by Wiseco. For more information, please visit our website at wiseco.com
the piston moves twice its stroke distance per revolution, 4000feet per minute = 48,000 inches, 4500fpm = 54000 inches

example a 350 sbc with its 3.5" stroke =7" per revolution, so 4000fpm =6850 rpm as a fairly reasonable limit with stock components, swap to all balanced and forged components and ARP fasteners and you can push the limits briefly to 4500fpm or 7700rpm but that is very unlikely to allow the engine to live long and remember the valve train probably won,t hold up near that rpm level and your unlikely to make effective power because just filling the cylinders becomes extremely difficult because you need to open the valve, fill the cylinder , burn the mix, exhaust and refill the cylinder 64 times a second at that rpm

RING END GAP CLEARANCE needs to be carefully checked

The piston ring's end gap can have a significant effect on an engine's horsepower output. Rings are available both in standard gap sets, and in special "file fit" sets. The file fit sets allows the engine builder to tailor the ring end gaps to each individual cylinder. Ring gaps should be set differently dependent upon the vehicles use, within the range of .003" (for the 2nd. ring) to .004" (for the top ring) per inch of cylinder diameter. The more severe the use, the greater the required end gap (assuming the use of similar fuels and induction systems). Engines having low operating temperatures, such as those in marine applications is too small. The chart below is a general guideline for cylinders with a 4.00" bore, adjust the figures to match your engine's cylinder diameter:

Top Rings (ductile iron, 4" bore)


Nitromethane .022 - .024"

Alcohol .018 - .020"

Gasoline .022 - .024"

Normally Aspirated - Gasoline

Street, Moderate Performance .016 - .018"

Drag Racing, Oval Track .018 - .020"

Nitrous Oxide - Street .024 - .026"

Nitrous Oxide - Drag .032 - .034"

2nd Rings (plain iron, 4" bore)


Nitromethane .014 - .016"

Alcohol .012 - .014"

Gasoline .012 - .014"

Normally Aspirated - Gasoline

Street, Moderate Performance .010 - .012"

Oval Track .012 - .014"

Pro Stock, Comp. .012 - .014"

Nitrous Oxide - Street .018 - .020"

Nitrous Oxide - Drag .024 - .026"



When installing new rings, the single greatest concern is the cylinder wall condition and finish. If the cylinders are not properly prepared, the rings will not be able to perform as designed. The use of a torque plate, head gasket, and corresponding bolts are necessary to simulate the stress that the cylinder head will put on the block. Main bearing caps should also be torqued in place. The correct procedure has three steps. First the cylinder is bored to approximately .003" less than the desired final size. Next it is rough honed within .0005" of the final diameter. Then a finer finish hone is used to produced the desired "plateau" wall texture. Use a 280 - 400 grit stone to finish cylinder walls for Plasma Moly rings.

Note - the "grit" number we are referring to is a measurement of roughness, it is not the manufacturers stone part number (a Sunnen CK-10 automatic hone stone set #JHU-820 is 400 grit). The cylinder bores should be thoroughly scrubbed with soap and hot water and then oiled before piston and ring installation.

Piston ring grooves are also sealing surfaces, and must be clean, smooth and free of defects. Ring groove side clearance, measured between the ring and the top of the groove, should be between, .001" and .004".

Id call the piston manufacturer and get their tech guys feed back, you'll generally want about a .005 piston to bore clearance with forged pistons but every piston design and manufacturer will have the required specs on file for every piston they make ,that should be carefully followed
don,t forget to ask about ring end gap,ring thickness,ring back clearance and ring groove size, quench distance, compression height, valve notch clearances and cylinder bore hone grits to be used,what piston pin and retainer should be used and what the pistons should weight, always ask "what else should I know?" and "what would be YOUR suggestions here?"

ID suggest trying for a MINIMUM of .038-.044 on a 496 BBC for quench as the long stroke bbc, or any BBC run over about 6000rpm with a 4" or longer stroke) tends to allow the quench clearance distance to tighten up a bit at high rpms, as parts stretch under stress/inertial loads


damage like this is rather frequently the result of the piston rings gap being too tight, the rings ends touch as they expand,
due to excessive heat and with no clearance the rings temporarily lock against the bore wall, the result is a broken ring, and fractured piston ring groove
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Staff member

Aluminum Alloys for Pistons

United Engine currently uses gravity feed permanent molds to produce aluminum pistons. Aluminum, alloyed with copper,magnesium, nickel and silicon are common piston alloys in use today.

Silicon is the major alloying element added to the aluminum. It offers a number of benefits in the area of piston production and piston operation.
Machinability Corrosion Resistance
Weight Reduction
Improvement in Hardness and Strength
Improvement in Expansion Characteristics
Improvement in Wear and Scuff Resistance

Aluminum silicon alloys used in pistons fall into three major categories: eutectic, hypoeutectic and hypereutectic. Probably the easiest way to describe these categories is to use the analogy of sugar added to a glass of iced tea. When sugar is added and stirred into the iced tea it dissolves and becomes inseparable from the iced tea. If sugar is continuously added, the tea actually becomes saturated with sugar and no matter how much you stir, the excess sugar will not mix in and simply falls to the bottom of the glass in crystal form.

Silicon additions to aluminum are very similar to the sugar addition to the iced tea. Silicon can be added and dissolved into aluminum so it, too, becomes inseparable from the aluminum. If these additions continue, the aluminum will eventually become saturated with silicon. Silicon added above this saturation point will precipitate out in the form of hard, primary silicon particles similar to the excess sugar in the iced tea.

This point of saturation in aluminum is known as the eutectic and occurs when the silicon level reaches 12%. Aluminum with silicon levels below 12% are known as hypoeutectic (the silicon is dissolved into the aluminum matrix). Aluminum with silicon levels above 12% are known as hypereutectic (aluminum with 16% silicon has 12% dissolved silicon and 4% shows up as primary silicon crystals).

Pistons produced from these alloy categories each have their own characteristics. Hypoeutectic pistons usually have about 9% silicon. This alloy has been the industry standard for many years but is being phased out in favor of eutectic and hypereutectic versions. Most eutectic pistons range from 11% to 12% silicon.

Eutectic alloys exhibit good strength and are economical to produce. Hypereutectic pistons have a silicon content above 12%. r>

It is the primary silicon that gives the hypereutectic its thermal and wear characteristics. The primary silicon acts as small insulators keeping the heat in the combustion chamber and prevents heat transfer, thus allowing the rest of the piston to run cooler. Hypereutectic aluminum has 15% less thermal expansion than conventional piston alloys."


Hypereutectic -vs- Forged Pistons

Hypereutectic pistons are used in some original equipment engines. They are favored because of reduced scuffing, improved power, fuel economy and emissions.

Hypereutectic 390 refers to a unique aluminum piston alloy that contains dissolved and free silicon. The material can be T6 heat treated to high strength and stiffness. Non-heat treated 390 hypereutectic alloy aluminum has slightly less strength than conventionally cast F-132 aluminum.

With this in mind, we caution the reader about the use of non-T6 heat treated O.E. design hypereutectic pistons for high performance. Silvolite and others do make replacement-type hypereutectic pistons that are worthwhile for stock replacement applications. Original equipment design is almost never suitable for performance applications.

The KB line of hypereutectic pistons were designed around the 390 alloy. The result is a high performance part intended to give the performance engine builder access to the latest in piston technology.

Forgings have long been the mainstay of the performance business and did well in the big cubic inch engines of the 60’s. Now, with focus on peak cylinder pressure timing, ring sealing dynamics, cylinder air tumble and swirl, combustion chamber science, and extended RPM ranges, we need to consider some new piston options.

The KB T6 hypereutectics are considerably different than the forgings. The KB pistons have shown improvement in power, fuel economy, cylinder sealing, service life, and cost effectiveness. The reduced thermal expansion rate allows the piston to be run with reduced clearance. A tight piston is less likely to rock, make noise, and burn oil. A rocking piston wears rings and increases blow-bye. The close fit of the KB piston allows the piston rings to truly seal, minimizing blow-by.

The design flexibility enjoyed by the KB series of pistons has an advantage over present day forging practices. The die for a forged piston must be designed so it can be easily removed. This limitation makes it difficult to make a light weight piston without sacrificing strength.

The KB pistons' utilization of the permanent mold with multiple die parts allows undercut areas above the pin hole and material distribution in the skirt area that stiffen the entire piston unit. The forged piston requires thick skirts to achieve comparable piston rigidity. A rigid piston rocks less in the cylinder and improves ring seal.

The forged pistons' thick skirts add weight. The design of KB pistons gives us the option to build the lightest pistons on the market.

Some current KB pistons are not super light for several reasons. If the piston is to be used as a stock replacement, more than a 10% weight reduction will mandate that the engine be re-balanced.

Common sense suggests that the introduction of a new product be extra strong at the initial release. As the product becomes accepted, weight reductions are scheduled as regular product upgrades, as justified with actual race testing.

There will always be a market for custom forged pistons. Small runs of forgings are more economical than small runs of permanent mold pistons because of the complexity of permanent mold tooling. Where quantities justify, expect to see future KB pistons developed that are lighter and stronger than anything else on the market. Machined head profiles are easily changed with our CNC equipment so we will stay current with new cylinder head developments. Volume production is expected to keep the price reasonable."


Staff member



a good example of why higher rpms and heat and cast and most hypereutectic pistons don,t play well together


Staff member
Which Mahle Piston Is Right For Your Engine?
Comparing the 4032 and 2618 forged wrought aluminum alloys
From the November, 2010 issue of Mopar Muscle

heres the catalog

Phone: 310 370 5501

Mahle Pistons Chrysler Hemi

Unless you rebuilding an engine with little to no budget you're going to upgrade to aluminum forged pistons. Besides being stronger than cast pistons, the lighter aluminum cuts parasitic power loss. That translates into more power at the wheels.

Recently Mahle showed us that there are distinct differences between their 4032 and 2618 alloys. The choice to use one over the other depends on your project. Are you building a street/strip machine or an all out racer? Choosing the wrong one can be devastating. To better understand, we'll let MAHLE explain.

4032 is a high-silicon, low-expansion alloy. Pistons made from this alloy can be installed with tighter piston to bore clearance, resulting in a tighter seal with less noise. 4032 is a more stable alloy, so it will retain characteristics such as ring groove integrity, for longer life cycle applications. Relative to 2618, 4032 is a less ductile alloy, making it less forgiving when used with boosted and/or nitrous applications.

The majority of Mahle forged PowerPak kits are made with 4032 alloy and require no additional piston-bore clearance. Mahle pistons are perfectly engineered to allow for the proper clearances assuming normal operation. For example, Mahle pistons for a small block engine will provide proper .0025"-.0030" clearances--right from the box.

2618 is a low-silicon, high-expansion alloy that is used for extreme-duty racing applications such as NASCAR, ALMS, etc. Due to its high-expansion characteristic, this alloy is engineered with additional piston to bore clearance. At the start of a cold engine, the pistons expanding process can be heard and is commonly referred to as the "piston slap". Once the engine warms up the noise subsides as the piston expands to its running clearance. 2618 is a more ductile alloy and grants higher tolerances with higher resistance to detonation. The forgiving characteristics allow for the most extreme conditions, but longevity is eventually negotiated after countless heat cycles.


Mahle pistons are designed for specific applications with the alloy that is best suited for that particular application.
but keep in mind the better versions of forged pistons tend to have the advantage in both strength and heat tolerances

......................Piston Alloy Comparison
...................................................... 2618
High silicon............................................No silicon
Low expansion........................................expansion
Tighter piston-to-wall clearance................More Piston-to-wall clearance needed
Quiet Operation......................................Noise when cold
Less ductile............................................More ductile
More stable & consistent.........................Higher resistance to detonation
Longer life cycles....................................Shorter life cycles



http://aftermarket.federalmogul.com/en- ... 7ibJ7FwU4M




http://www.trickflow.com/search.asp?Ntt ... wordSearch




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Staff member
EngineLabs: PowerPak pistons are made from either 4032 or 2618 aluminum alloy. Please explain the pros and cons of each alloy and why certain applications get the 2618?

McFarland: These two alloys are similar in many respects. In terms of overall strength the 2618 edges 4032 out by a small margin. Silicon content makes up the main effective difference with the 4032 alloy containing 12-13 percent silicon compared to 2618 alloy having 0.2 percent or less. Silicon reduces heat expansion, while being hard increases wear resistance. The decrease in expansion allows for tighter clearances, reduced wear on both the piston and bore, also resulting in quieter operation. The hard silicon element greatly helps to increase the number of heat cycles the piston can endure before ring grooves and skirts start to distort. This makes the 4032 alloy well suited for a wide range of applications from street performance to upper level sportsman racing. The 2618 alloy is more malleable, allowing it to flex and move under extreme loads further and more frequently before reaching the point of fracture. This gives the 2618 alloy a greater resistance to the shock loads of detonation. The compromise is that the alloy softens at a much faster rate, allowing the piston to distort more rapidly. This makes the 2618 alloy best suited for extreme-duty race applications where the engine will be serviced on a regular schedule. Mahle uses the 2618 alloy for extreme-duty applications or those that have a high likelihood for experiencing aggressive and or frequent detonation. Due to the increased wear resistance and longevity characteristics of the 4032 alloy, Mahle uses this alloy on a wider scale.

EngineLabs: As head designers strive for smaller combustion chambers, how does this trend affect piston design?

McFarland: For high-compression motors, there’s a definite advantage to removing the piston dome and being able to run a flattop or shallow dish. When these same heads are used in other applications, there will have to be compromises, depending on the stroke/rod configuration used and the desired compression ratio. Long stroke/short CH pistons have physical limitations to how much dish volume is available before you start to run into the top of the connecting rod. Larger volumes in the pistons also result in less available quench area.


solid fixture here in the forum
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solid fixture here in the forum
Good read.
Read all above tonight Grumpy.
4032 is good for up to 650 Hp .
Above 650 Hp you want 2618.

Gotta bite the Bullet for Diamonds.


solid fixture here in the forum
Venolia was the only company that I know of that full Hard Anodized their Race pistons too Grumpy.
Had the distinctive Gray Color.
Special process to control anodized thickness precise.


solid fixture here in the forum
Keith Black Hyperuentic pistons are likely the very Best pistons you can buy for a long life High po street engine to last 200,000-400,000 miles.
Made nice.
All the features of top quality drag pistons.
A few Pontiac guys have used to 800 Hp no issues spraying NOS.
But a risk yet....
2618 Diamonds Best at least for me.
Need custom Pin setting.

Bought a set for 1 455.
K.B. Hypers.
Save for the Crower Forged 4340 steel rods.

Diamonds for Crower Ti.


The Grumpy Grease Monkey mechanical engineer.
Staff member
modifying piston domes for increased valve flow, and proper clearances.

I was recently asked to stop by a guys shop and examine an engine,
in the process of assembly, I brought a few basic tools,
it was rapidly obvious that the piston domes were contacting the combustion chamber at TDC, thankfully the contact area was very limited and once we use some modeling clay strips in the combustion chamber
,it was very obvious that a machine shop could easily mill off a very small edge of the piston dome at about a 60 degree angle on one edge of the piston dome , removing maybe 2 cc in volume and that would result in a major problem being totally avoided.
in any engine build the pre-assembly clearance checks can help you avoid very potentially expensive mistakes,
in one way the piston actually contacting the combustion chamber was a minor blessing,
as the fact forced the guy building the engine to stop and ask questions...
consider what might have happened if the piston cleared the combustion chamber contact with lets say a minimal .005 thousands clearance,
it would be almost assured to hit and cause issues under actual operational conditions.
while I was there we checked valve to piston clearance,
this was only about .020 thou on the exhaust valves,
which was something very easy to have a local machine shop rectify, by marginally expanding the valve notch diameter and depth,
but again a factor that could easily be over looked as nothing was binding during the test assembly,
yet it was almost a potential 100% death sentence had the engine been assembled and run that way at high rpms,
without making the required mods for required reasonable minimal clearances.
I also suggested he have a flame front groove from the spark plug area over the piston dome milled as it may reduce the engine tendency to get into detonation.






dial indicator with stand


Fig. 2.4. This computational fluid dynamics illustration shows air entering the cylinder during the overlap period. At this stage of the intake event, the air that exits the short side turn runs into the wall of the valve cutout. This reduces the effectiveness of the overlap period and typically reduces the volumetric efficiency more than it might be supposed.



When any dome-top piston is used, such as this JE slug, it is necessary to verify dome-to-cylinder head clearance. This can be accomplished by using clay or Dykem layout fluid. With our piston slathered up, we saw no transfer to the cylinder head (without a gasket). This means we will have at least our gasket compressed thickness (0.040-inch) clearance when the head is installed.

The next step is to verify piston-to-valve clearance. We installed checking springs on the intake and exhaust valves, turned the engine to 10 degrees before TDC (top dead center) for the intake and subsequently 10 degrees after TDC for the exhaust and used a dial indicator to measure free drop. With our relatively conservative lift, there was miles of clearance.



Next, we checked radial valve clearance using a transfer punch inserted through the valveguides. The corresponding punch mark on the pistons was scribed using a compass set to half the valve diameter. This check ensures the valve faces fit inside the valve pockets.


Fig. 2.5. Here are the two ways to relieve shrouding, which is caused by the valve pocket wall. The simple way is shown on the left and the more effective but tedious method is shown on the right.


Fig. 2.6. To appreciate what is going on here, first locate the ghosted image of the intake port and chamber and orientate that with the pressure differential contour lines around the valve. These contour lines show the pressure differential between the valve and valveseat on a 24-degree head as the valve progresses through its lift.Although this appears to be a subject for Chapter 4, Cylinder Heads, the flow pattern developed has a strong influence on how the top of the bore and piston should be shaped. You need to recognize that the busiest area with the highest velocities occurs between the 9:00 and the 10:30 o’clock position. The edge of the bore and the piston dome can block flow in this region unless steps are taken to prevent it. The arrow indicates airflow through the port into the cylinder.

be aware you may find that the machine shop cost of custom machining pistons
for increased valve clearance may cost a significant percentage of the cost of buying new (IDEALLY FORGED PISTONS) and keep in mind that pistons with domes that build increased compression are generally designed for the required valve clearance of high lift cams, while standard cast or hyper eutectic pistons may not have the required thickness in the required areas that allow deep valve relief cuts


Fig. 2.7. Indicated here are the areas of a typical high-compression piston that need attention as far as valve pocket shrouding is concerned.

Less obvious is that the fl ow pattern on the cylinder wall side of the port is spiraling past the edge of the bore shrouded intake valve. In effect, air is corkscrewing past the edge of the intake valve at about the 10 o’clock position, and during the overlap, the dome of a high-compression piston can block this flow. This suggests that you not only need to cut the top of the bore as discussed in Chapter 1, Displacement Decisions, but you should also find out if the piston dome can have any negative influence on the flow into the cylinder other than the effects of valve shrouding from the aspects indicated in Figure 2.3. From Figure 2.6, you can see that the flow into the cylinder does not follow a pattern that is by any means intuitive.

This flow test and the port probing just prior to the intake valve show an important flow pattern. As unlikely as it may seem, the flow corkscrews off the edge of the valve on the cylinder wall side of the port and then proceeds over the edge of the intake valve and into the cylinder. At least that is the way it would go if there were no obstructions. Because this flow pattern is generally unknown, piston domes rarely have a form that makes allowance for it. Depending on the height of the dome there is a potential 10 to 15 hp to be had by some subtle and some less than subtle reshaping.


reading the related links provides a good deal more details and could easily be well worth the time and effort in the avoided cost incurred from mistakes

read related linked info















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solid fixture here in the forum
Thanks for the Read again today Grumpy.
Most useful when you add your own writings.
Personal experiences shared.
I do take mental notes.
Not wrong advice from you.