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Piston Tech

Posted 03-02-2002 at 01:00 AM by MichaelDelaney

INTRODUCTION There appears to be some confusion out there as to whether LOW silicon-containing pistons are better for high performance street engines. This can be seen in one discussion over on another honda forum, where one person was advocating for the use of Ross low silicon-content, forged racing pistons over the other forged pistons containing more moderate silicon content like Jun, Wiseco, JE/SRP, Mahle, and Probe Racing. If you're not building a trail queen racing car, do you need to have ultra low silicon containing pistons? Not from what I've understood to be true and so, I thought I'd share some technical info on piston tech with you here to explain some basic things to consider when you shop for pistons in your engine package. BTW please notice that it is silicon and NOT silicone which is used for breast implants and bathroom caulking. A Little Brain Teaser Quiz Before We Start: Can you tell the difference between these 2 highly successful, ultra performance race-only very high static CR forged N/A pistons ? : Hint: Yes there is a difference and it makes a theoretical and practical difference in burn efficiency. I'll have more to say about this later on in this article. A. EFFECT OF BETTER ENGINE PERFORMANCE AND STRICTER EMISSION REQUIREMENTS ON PISTON DESIGN 1. Higher Top Ring Location : to reduce hydrocarbon emissions. The "dead space volume" above the piston up to the top of the cylinder wall usually traps unburnt fuel and burns less completely...producing more emissions. Reducing this volume, by moving the top ring up , decreases emissions. The top ring is now exposed to hotter temperatures and must be stronger. However, moving the top ring up is not just for emissions purposes either: Here you see a higher top ring and piston pin location placed at the level of the oil ring groove, both of which allows for a longer rod and better rod ratio in these forged race-only strutted pistons. The Rod is 0.25 in. or 6.4mm longer than the stock rod here. If the oil ring is moved up into the piston pin location, it's overall ring-sealing effectiveness will be reduced. You can get away with it, if you exert a vacuum on the crankcase (eg. by using a Moroso block vacuum pump to achieve less ring blow-by), but then you're driving an additional pump (more parasitic losses) in the system. You don't want to go too high though, especially in FI applications. The minimum top ring spacing is 0.250 in. Moving the top ring down improves durability but at the same time, creates a situation where more entrapment of unburned gases will occur locally in that area, leading to a less efficient burn. According to Endyn, in an ideal world, the top ring would be even (in height) with the top of the piston to achieve a better burn efficiency but the piston's valve reliefs won't allow for this to happen. The use of several indentations in the piston above the top ring works well to protect the top ring that is mounted higher than usual. The piston valve reliefs dictate where the upper ring goes and these indentations do the rest. 2. Narrower Piston Ring Area on Piston and Lower Deck Height (Shorter Blocks) on Engines : to allow for a longer rod (for a higher rod ratio) but still have everything fit within a lower deck height and also allow for a lower hood line. This reduces the piston space available for rings. Rings must be thinner/narrower and lighter but still seal as well as thicker rings. Thinner rings mean the piston ring land will also be thinner requiring a stronger piston alloy material. Also, the onset of ring flutter is determined from ring width and the maximum piston acceleration during its cycle. Paul Dykes (of Dykes piston ring fame) determined that thinner rings are less susceptible to flutter than the fatter rings. (Based on his research he designed an "L" shaped ring which could never suffer from flutter). 3. Tighter Piston to Cylinder Wall Clearances: to reduce blow-by (from the combustion chamber to the crankcase), reverse blow-by (from the crankcase to the combustion chamber on the intake stroke), achieve better burn efficiency, and reduce emissions. Piston rings must seal (for good compression pressures and prevent oil from getting into the chamber) , have shorter break-in period, and wear the walls less despite being closer. These 3 requirements have made piston manufacturers develop new alloys and coatings for pistons and rings to make them withstand the higher tolerances demanded by the design requirements. I'll discuss what some of these new materials and coatings are below. B. TYPES OF PISTONS There are 2 types of ways to make pistons: Casting and Forging. 1. Cast : - Casting means that molten liquid aluminum is poured into a mold that is in the shape of the piston. - they are "WEAKER" than forged pistons and prone to cracking with use of nitrous and boost. For example the Nissan OEM cast pistons typically crack at the number 2 ring land. There 2 types of CAST pistons based on their silicon content.: 1a) Standard Cast (< 12.5% Silicon Content) - Expands uniformly but more than any other type of piston when heated - Needs loosest intalled piston to wall clearances , since expands most due to low silicon content when heated. - Noisiest on cold engine start up and has the most blow-by of the 3 piston types in a cold engine because it has the least silicon content and therefore expands the most when the engine warms up from being cold causing it to require larger piston to wall clearances. - requires reinforcement plates or struts near wrist pin area, since alloy expands more as temperatures increase. These struts often crack under high loads like detonation. - requires ring groove insert to withstand ring land pound out and wear 1 b) Hypereutectic Cast (>12.5% Silicon Content, Most are 16-22% Silicon) Hypereutectic is an adjective that refers to the silicon (same material found in sand) content in the piston. Hypereutectic means the piston has MORE silicon added to the mixing with aluminum alloy. Note that this is not SILICONE. Eutectic means 12-12.5% silicon content. Hypereutectic means > 12.5% silicon content. Special melting process combines silicon to "super-saturate" the aluminum alloy. Special molds and casting- cooling processes are needed to get fine dispersing of silicon evenly or uniformly throughout aluminum alloy. There are hypereutectic cast pistons available. These are more resistant to wear and scuffing, expand less with heat, and are stronger (more able to withstand higher cylinder temperatures , pressure, and detonation than standard cast.) More silicon, if uniformly added to aluminum alloy, : - Hardens the aluminum alloy further - Expands less with heat (higher themal expansion co-efficient) meets criteria for piston design: run tighter clearances. Hypereutectic pistons are stronger and can run narrower ring lands and tighter piston-to-wall clearances, since there is less heat expansion than standard cast. No wrist pin area re-inforcement plate is needed due to less rapid expansion with heat. - No iron ring groove insert is needed to protect against ring land pound out. Ring groove is more heat and wear resistant with higher silicon. - But extra hardness also makes the piston MORE BRITTLE (i.e. brittle meaning that it's easier to crack under stress and loading, like high rpms or under boost or detonation) and therefore must be handled more carefully on install. Not all hypereutectic pistons are alike. The size of the silicon granules used and how well the silicon is mixed (distributed) in the aluminum alloy during the casting process affects the quality. If unevenly added and mixed, the silicon clumps and forms hard spots in different parts of the piston which crack more easily under high loads. MOST STOCK OEM PISTONS ARE HIGH SILICON CAST. 2. Forged - the process of making a forged piston involves heating a slug of aluminum alloy that is in the shape of a long cylinder and then pressing it into the die's piston shape under very high pressure, and then machining the surface. The mixture of ingredients in the metal is already in place and there is no adding and mixing like in casting where they added the silicon to the aluminum. - Forging creates a DENSER AND LESS BRITTLE (600% more ductile or less porous) grain STRUCTURE that is stronger than cast[/b] piston's crystalline grain structure. Forged pistons can handle nitrous and high boost (temperature resistant and stronger) better than cast pistons. - Forged pistons have high silicon content already mixed in the alloy but have less silicon than OEM hypereutectic cast pistons. For example, an aftermarket forged Wiseco piston has 7% less silicon content than OEM Honda hypereutectic cast pistons. - The less porous forged piston conducts heat faster and runs 20% COOLER than cast pistons (even hypereutectic cast) reducing higher (detonation-inducing) temperatures. There is better HEAT TRANSFER AWAY from the piston crown with forging. The heat can be transfered to the cylinder head (eg. when the piston is at the top of the exhaust stroke) and wicked away by the coolant flowing through the cylinder head. - Forged pistons have greater thermal expansion than hypereutectic cast pistons and have greater clearances and can be noisier and may have more blow-by in a cold engine compared to hypereutectic cast pistons but it's NOT as noisy as eutectic or hypoeutectic standard cast pistons. Once the engine is warmed up, the clearances will then tighten and there is less noise from piston rock as it travels up and down the bore. In fact, this is another advantage of forged pistons: They seal up and close up the clearances better than when heated. The trick of the racing engine builder's trade is to find the lowest cold engine clearances that they can choose so that when the forged pistons expands at warmup, the clearances are ultra-tight to get better engine compression and less leaking. The looser installed clearances with forged are not as bad as you would think:
Quote:
Originally posted by Mike Kojima at Sport Compact Car Magazine Old school forged pistons needed to run as much as 0.009" piston to wall clearance. These pistons sound like a diesel engine, rattling like crazy.(However), recent advances in piston alloys and skirt design, modern forged pistons can be run as tight as 0.006-0.003". Pistons that run on the high side of this scale will still rattle. Ones on the low side can be fairly quiet. Usually this has to do with the silicon content of the alloy. Low silicon pistons are the ultimate in strength and toughness but require big clearance because of the metal's high expansion rate. These are pistons used in top fuel drag racers or the real nasty turbo Hondas. High silicon pistons run tighter clearances and are slightly less ductile but are still much stronger than cast pistons. I would not recommend a low silicon piston for street use no matter what. It would be noisy, wear rings quickly and be a oil burner after not so many miles. If you are going to push the edge with turbo boost, nitrous or are going to do some real racing, forged pistons are the way to go.
C. ANTI-FRICTION PISTON SKIRT COATINGS Why put coatings on your pistons?: - used to reduce wear and scuffing problems - coating thicknesses run in the order of 0.0010 in. - computer controlled spraying of coat onto piston prevents overspray into the ring grooves and then cured. Honda uses molybdenum (moly)-based coating on their ITR and CTR pistons. Federal Mogul, for example, uses moly-graphite-based coating on their piston skirts. - must have proper skirt clearances especially with tapered skirts: measure piston to wall clearance 90 degrees to the wrist pin (called the major axis) just below the pin centerline and then add the skirt clearance to this to get the proper bore size. minimum clearances are based on non coating measurements but do not measure the skirt and compensate for the increase in diameter due to the skirt coating as this could result in excessive clearance and possible piston failure. Some race-only pistons remove the piston skirt contact with the walls altogether and recess them back. In addition to providing more strength and rigidity to the piston itself, these "strutted" pistons also place an emphasis on reducing friction-robbing power from skirt wear on the walls, as the piston travels along the swept volume. This, however, also places a lot of stress on the rings and piston and piston ringlands because they will now bare the brunt of the piston sideloading against the wall, as race engines tend to run very, very tight piston to wall clearances. The tighter clearance is also needed to minimize piston rock with a strutted piston. Needless to say, these pistons are not meant for your daily street performance engine which shouldn't need rebuilding for at least 50-60,000 miles due to the extra wear. Race engines with aluminum blocks now use Nikasil-coated liners to reduce this hp-robbing parasitic loss. D. PISTON RINGS TECH There are typically three rings used : the top and middle rings are used to keep combustion gases from escaping the combustion chamber, and the bottom ring, often called the oil control ring, prevents oil from leaking into the chamber. Originally Posted by www.automotiverebuilder.com Rings are getting thinner and narrower to both reduce inertia and to improve sealing by allowing greater conformability to the cylinder bore. Most top rings today are 1.2 to 1.5mm, with some Japanese rings as small as 1.0mm or even less. Most oil rings are now in the 3.0mm size, and provide much less tension. The oil ring alone used to account for up to 25% of an engine's internal friction, but today the number is down around 12-18%. "One area where we're going to see big changes is in ring coatings," said Wilkinson. "Back in the 1950s, chrome was the most common type of facing material for rings. Moly was introduced in the 1960s, followed by plasma spray moly coatings in the 1970s. We think chrome plating will be going away because of environmental reasons. The Japanese use nitriding to increase the wear resistance of their ring sets. Nitriding does not have the scuff resistance of plasma spray moly, but it gets rid of the chrome. We're developing nitrided oil rings now for some OEM applications," said Wilkinson. Gas nitriding, which should not be confused with the black phosphate coating that is currently used on most rings to prevent rust during shipping and storage, is a heat treatment process that impregnates the surface of the metal with nitrogen in order to harden the surface of the metal. This makes the rings very hard about 68 on the Rockwell C scale for improved wear resistance. "One of the advantage of the plasma spray process is that different materials such as chrome carbide can be mixed with the moly powder to produce different ring characteristics," said Wilkinson.... "We can manufacture rings that don't wear (themselves), but they wear the cylinder bore. So we have to balance ring and bore wear to come up with the best overall solution.".... The increased demands on today's engines means more OEMs are using ductile and steel top compression rings. As mentioned earlier, these tougher materials are needed to withstand the pounding and heat. Gray cast iron is an adequate ring material for most older passenger car applications. But the change to thinner low tension rings in newer engines, and the relocation of the top ring closer to the top of the piston, has dictated the use of ductile iron or steel top compression rings in many applications. Gray cast iron is a brittle material that can easily break if mishandled. Rings made of this material may also break if the engine experiences heavy detonation. Ductile iron (also called "nodular" iron), on the other hand, has a different microstructure with rounded grains instead of rectangular grains. This allows the metal to bend without breaking , so it can withstand detonation in high load engines. It also makes the metal about twice as strong as gray cast iron. Chrome or moly faced ductile iron 1.5mm top compression rings have been used since the early 1980s in many turbocharged engines, and are now used in many late model domestic engines with the new piston and ring configurations. Gray cast iron rings are still common in aftermarket ring sets, but many premium ring sets now have ductile iron top rings. Another ring material that is seeing greater use in new engines is steel. Twice as strong as ductile iron and four times as strong as gray cast iron, steel can provide the durability and toughness needed for the most demanding top ring applications. Steel rings have a tensile strength in the range of 240,000 psi, which compares to 180,000 psi for ductile iron and 45,000 psi for gray cast iron. Hardness can vary depending on the alloy and heat treatment, but is generally in the 44 to 53 HRC range compared to 38-40 HRC for ductile iron and 22-23 HRC for gray cast iron. Like ductile iron, steel is not compatible with cast iron cylinder walls so it must be coated with either chrome or moly, or nitrided. Most of the steel rings currently in production have a width of 1.0 to 1.2mm....Steel rings are usually barrel faced, having contoured outside diameters which give the ring a center contact with the cylinder wall. Though the best advice here is to follow the OEM lead and replace ring sets with ones made of the same material (or better), several ring manufacturers said steel and ductile iron rings are virtually interchangeable. If a steel replacement ring is not available for a certain application that uses steel as original equipment, a ring set with ductile iron top rings can be substituted. Federal-Mogul's Gabrielson says there are even some instances where the OEMs have gotten away from steel and gone back to gray cast iron. The use of knock sensors and more precise engine control systems on these engines has reduced the risk of detonation to the point where the added durability of steel is no longer necessary. When installing new piston rings remember to always check the end ring gap clearances according to manufacturer specs (a good rule of thumb for piston to wall clearances in Tegs is for every inch of cylinder bore use 0.0040-0.0043 in. ring end gap) and to lubricate with WD40 prior to installation to achieve a faster break-in rather allowing for the engine oil to wash down in between the ring-wall gap early on. For piston to wall clearances, if the pistons are of a low silicon alloy, use .003", but do not run less clearance. If the pistons are made from a high silicon content alloy, run them at 0.0026" to 0.0028", depending on the bore and application (N/A vs. FI). In race-only N/A engines, some people have gone as low as 0.0018-0.0022" with forged medium silicon pistons. However, these are not your 50,000-100,000 mile specials in terms of engines for obvious wear reasons. E. PISTON GAS PORTS
Quote:
Originally posted by www.rehermorrison.com ...a gas port is a hole drilled from the piston deck (a vertical gas port) or from the top ring land (a horizontal gas port) to the rear of the top ring groove. The purpose of a gas port is to apply combustion pressure directly to the top ring, forcing the ring face firmly against the cylinder wall. The number, size, and location of gas ports vary with bore diameter, engine type, dome design, and the engine builder's personal preferences. A typical big-block piston, for example, has between 12 and 16 gas ports that range from .040 to .060-inch in diameter. The fact is that all top rings rely on gas pressure to seal the cylinder on the compression, power, and exhaust strokes; static ring tension is primarily responsible for sealing on the intake stroke, when low pressure exists in the cylinder. In a piston without gas ports, the ring is pressurized by gases that work their way to the back of the ring through the clearance between the ring and its groove. Production pistons customarily have .002 to .004-inch side clearance to allow this pressurized gas to reach the cavity behind the ring. Gas ports pressurize the back of the ring directly, so the ring-to-groove clearance can be reduced significantly. Tight side clearance helps to stabilize the ring in its groove, preventing ring flutter and reducing blowby. Recently an A-B dyno test with a high-horsepower big-block dramatically illustrated the benefits of gas ports. Although we customarily use gas ports in our 565ci Super Series engines, we built an engine without them at the customer's request. When we dyno tested the engine, it was off more than 50 horsepower from similar engines we'd built. The engine didn't hold pan vacuum over 7,000 rpm, and it wouldn't pull to peak rpm. We pulled out the pistons, drilled gas ports, and reassembled the engine. We didn't change the rings and didn't hone the bores, so the only difference was the gas ports. When we put the engine back on the dyno, the power was right where we expected it to be, the crankcase had good vacuum, and the engine pulled cleanly to its redline. That back-to-back test convinced me that gas ports really work . Why do gas ports make power? Gas ports bleed off pressure behind the rings quickly, so there is less friction to overcome. They also allow an engine builder to use thinner rings with less radial tension, which frees up additional power. The only time you want a compression ring to be forced tightly against the cylinder wall is on the first third of the combustion stroke when cylinder pressure is highest. For the remainder of the ring's travels up and down its cylinder, you would like to have it loaded as lightly as possible while still maintaining an adequate cylinder seal. Do gas ports wear out rings prematurely? I don't see any discernible difference in ring wear with and without gas ports. After all, it's cylinder pressure that forces the ring face against the wall; gas ports are just a more efficient way to apply this pressure.
Quote:
from Ross Pistons website: Gas Ports (Top and Side) allow cylinder pressure to go directly behind the top ring and aid in sealing. Gas Ports are very effective when used with tight ring grooves and high ring positioning. Not recommended with blowers, dyke rings, or in endurance motors.
From Ross' site, you can gather that piston gas ports are better for racing engines only, since the ports can become clogged and lose their function in endurance racing and therfore not good in a high performance daily-driver. ---------------------------------------------------------------------- F. Questions for Clarification From Team Integra Members on Piston Tech Article : Questions Originally Posted by Conrad Maranan 1. So what piston manufacturer produces the highest silicon content in a forged piston? Apparently OEM Honda forged pistons have the highest silicon content. In terms of aftermarket pistons, Jun, JE/SRP, and Wiseco have hypereutectic silicon content. The Wisecos have, as I said in the post, about 7% less silicon than OEM Honda. You can ask Jeff Schaeffer how much silicon are in the Probe Racing pistons he uses in the Dominator blocks since I don't know Probe pistons that well but the clubsi.com thread said they are in between Jun (highest of the forged aftermarkets) and Wiseco. The forged Arias and Ross pistons have the lowest silicon content. 2. What are the major downsides to having too much silicon and what is considered to be too much? What do you think of Keith Black Silv-O-Lite hypereutectics? Don't know anything about Keith Black Silv-O-Lite hypereutectics. Maybe you can give me a link or share some info. Obviously being hypereutectic, it is a cast piston. I prefer forged. Adding more silicon makes the piston harder (plus side) but also makes the piston more brittle (downside). You have to find the balance of going hard enough to withstand high heat and pressure and some hits from detonation but not too much as to make the piston more susceptible to cracking with detonation (from being too brittle). This is why the aftermarket forged pistons I prefer do not have as much silicon as the OEM Honda R pistons but have more than the aftermarket standard cast pistons or Ross/Arias low silicon forged pistons. 3. With higher silicon content, would it be possible to run piston-to-cylinder wall clearances tighter than 0.003? This is THE big source of the confusion. It's all about relative clearances. The low silicon, standard cast or forged pistons (i.e. Ross and Arias forged low silicon) need the highest installed clearances and rattle/rock around in cold engines. The other forged pistons (JE/SRP, Jun, Probe, Wiseco) have more silicon than standard cast and Arias/Ross low silicon forged pistons. The silicon prevents expansion. So the installed clearances are tighter in these forged pistons than in standard cast or low silicon forged. OEM pistons have the highest silicon. They have the tightest installed clearances of all and least noise in a cold start. 4. Where do the hypereutectic cast pistons fit in? They are like forged pistons in that they have more silicon than standard cast and less silicon than OEM. So their clearances are tighter than standard cast but looser than stock. Compared to JE/SRP, Jun, Probe, and Wiseco forged pistons, the hypereutectic cast pistons have even more silicon and can run tighter clearances than the high silicon containing forged pistons. However, they are cast not forged. Remember, cast are less dense, more porous, and therefore, weaker overall than forged. That's what confuses people. The sales people try to confuse you with silicon content, how this affects having more or less clearances, and having more or less noise. Yes you can run tighter than 0.003 in. with forged pistons. That quote by Mike Kojima I put up was more related to Nissan forged pistons. In forged Honda aftermarket pistons, we can run as tight as 0.0026-0.0028 in. Jeff has run as tight as 0.0020-0.0022 in. on his racing engines (I have even heard someone try as low as 0.0018 once... I think it was Jeff or somebody who told me they tried this in a race-only engine!..It didn't last as the piston expanded past what the clearance allowed for) . But please remember these race engines with 0.0022 in. are rebuilt more often than street engines. Remember also, the forged pistons run less silicon than OEM which have the highest silicon and the tightest clearances. For the B18 (from my Helms manual) the clearance is 0.00040 in. (YES THAT'S AN EXTRA ZERO THERE ...IT'S NOT A TYPO ERROR....OEM = highest silicon, expands the least, therefore has the tightest clearance). 5. For a daily-driven, street/strip set-up, would you recommend hypereutectics over forged slugs? I personally prefer forged...they run cooler since their grain structure is more dense or ductile or less porous than hypereutectic cast pistons...so they can conduct heat faster away from the piston crown with a denser alloy. The forged pistons usually run looser installed clearances and are less brittle (stronger) compared to hypereutectic cast. 6. With the information that you provided me, I'm assuming that the ideal pistons for a daily-driven, street/strip Honda would be the CTR slugs. I was actually looking for slugs that would land my compression in the neighborhood between 12.0:1 and 12.25:1. Perhaps some re-welding and re-shaping of the combustion chambers would have to be effected if I wish to achieve my desired CR with the CTR pistons? for a daily driven street/strip Honda, I prefer forged medium silicon content pistons. OEM's are too brittle. The Arias and Ross are too noisy. The OEM forged CTR have very high silicon content and can run into issues if detonation occurs with that high of a static CR. The dome on the CTR has a lot of surface area which slows the burn rate. Using a stock 0.76 mm thick 3-layer head gasket, in a GSR, the addition of CTR pistons raises the CR to 12.3-12.4:1. In an ITR, it is around 12:1 and in an LS, the CR is around 11.7:1. Remember that the compression height on the CTR piston is larger than the ITR or GSR pistons and will bring the dome closer to the cylinder head. You have to nachine the head to accomodate this or else the piston to head clearance will be too small and you risk piston to head contact. Same for the piston's valve reliefs and piston to valve clearance - the compression height moves the dome closer to the valves. 7. Once upon a time, there was a lot of hype with moly coatings. Do you feel that their added benefits are reasonable for use in a daily-driver, or would that be overkill on a street car? The stock CTR and ITR piston skirts are moly coated. So it's not overkill to have skirt coatings and they are beneficial. ---------------------------------------------------------------------- G. SUMMARY Silicon reduces piston expansion with heat and hardens the piston but the more you silicon you add, the more brittle the piston becomes. There's a fine line between making the aluminum alloy harder to make it stronger and resistant to detonation/scuffing AND adding too much so it becomes too brittle and cracks with detonation. Honda added a lot more so they can have a quieter engine with tight clearances for the average car owner. 1. OEM Forged (ITR/CTR) highest silicon , most tightest clearance 2. Hypereutectic Cast: next highest silicon, next tighest clearance 3. Forged Higher Silicon (Jun, JE/SRP, Probe, Wiseco): medium silicon, in between clearances 4. Forged Low Silicon (Arias, Ross): low silicon, looser clearances 5. Standard Cast: lowest silicon, loosest clearances ---------------------------------------------------------------------- H. GENERAL HONDA OEM PISTON SPECS The Definitions of Clearances and Heights are shown here.: http://www.team-integra.net/forum/di...1&ThreadPage=1 Engine , Piston Dome Volumes, Compression Height, Dome Height, Weight: B18A/B (PR4) -3.2 cc , 29.97 mm, - 1.397 mm, 280 g. B18C1 (P72AO) -0.60 cc , 30.05 mm, 0.00 mm, 305 g. JDM GSR(P72OO) +2.52 cc B18C5 (P73AO) +3.64 cc, 30.23 mm, +1.78 mm, 310 g. JDM Spec R (P73OO) +5.96 cc B17A (P61) 0.00 cc B16A (PR3) +6.01 cc, 29.97 mm, +2.49 mm, 299 g. JDM B16A (P30) +6.93 cc B16B (PCT) +8.63 cc, 30.73 mm, +6.43mm, 327 g. B20Z (PHK) -4.04 cc B20B (P3F) -9.92 c, 29.59 mm, - 0.89 mm, 312 g. B18, B17, and B16 piston stock bore is 81mm, 81.25mm [b]
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