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12-25-2005, 05:40 PM | #26 |
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There's no way to weigh the actual weakness of the stock piston or the stock piston design...
For 1, we only only know which casting method they used and nothing else. We do not know any one the quality control info, on what poercentage of pistons would be expected to fail prematurely due to any number of external or internal related issues... Also... We have no control group of pistons or STi engines to compare 1 to another...no one uses the same fuel, lives in the exact environmental conditions (including weather, temp, humidity, etc), same elevation, etc...Also driving methods and distances can cause issues...care of the car can effect things also. Plus there's also tuning and other parts involved here... We will never know a true number or percentage of failures in STi pistons... This being said... Using better fuel, keeping tunes mild, not going for excessive boost amounts, or pushing the car at WOT 24/7, along with good car care should allow the pistons to last for their full life. This all being said...just don't be stupid with your car...and you should be ok. Unless you got the set of pistons that were in the percentage group of premature failure due to manufacturing defects...in that case, there's nothing you can do... Good write up...it's a solid place for people to begin.
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12-26-2005, 10:43 AM | #27 | |
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I love it.
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When comparing 2816 to 4032 the reflective silicon grains are not present. It's only the expansion of the alloy you need to consider. The difference in 2618 and 4032 alloy expansion is trivial. If you can run 2618 CP pistons at 0.0025, then you could run the same pistons made of 4032 at 0.0022. That's not a big deal. The difference between 2618 and 4032 is hardness. It's the ability of the metal to resist deformation when pressure is applied. A metal is 'harder' than rubber, but rubber is more "forgiving" to sudden shock. Likewise, but with less disparity, 2618 is more forgiving of detonation than 4032. A rubber piston might completely absorb detonation shock, but is would not last very long oscillating in a cylinder. |
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12-26-2005, 04:26 PM | #28 | |
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Here's a page showing Aluminum's thermal reflectivity at about 95%: http://www.mellesgriot.com/products/optics/oc_5_1.htm Here's a page saying that Silicon is "nominally transparent" at thermal wavelengths: http://www.ligo.caltech.edu/docs/G/G...G050059-00.pdf I think it's fair to say that silicon definitely does not reflect heat back into the combustion chamber. However, it may still be possible that an increased silicon content makes the aluminum piston more translucent to thermal energy, which would mean the thermal energy would go through the piston without heating the piston itself. Unfortunately, to make any significant difference, I would imagine the silicon content would have to be quite high, much higher than the 10-20% range in the near-eutectoid range. It would have to be very hypereutectic. Anyway ... "thermally transparent pistons" ... the next rage at NASIOC.com. -Adrian Last edited by SaabTuner; 12-26-2005 at 04:36 PM. |
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12-26-2005, 07:09 PM | #29 |
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This post is totally pointless ... but I just found and even better grade of Beryllium, Instrument Grade I-220H. It's 30% stronger than S-200 Beryllium!!
Now if I could just win the lottery ... |
12-29-2005, 12:07 AM | #30 |
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Why would you use beryllium as a piston material? Are you aware of the dangers associated with processing that material? There is more to a material than just the physical properties. Beryllium isn't used a whole lot as a primary material any more... (as an alloying element in things like copper, etc. it's still used)
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12-29-2005, 12:17 AM | #31 | |
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Here's some info off of the Subaru global site which talks about Subaru pistons, the coatings used, the skirt design, etc.
Quote:
http://www.subaru-global.com/about/parts/01.html |
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12-29-2005, 12:23 AM | #32 | |
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12-29-2005, 12:59 AM | #33 | |
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The reason for using it is its extremely high thermal conductivity (higher than Al, almost as high as Copper), high strength/weight ratio (almost as high, if not higher than, titanium) and high rigidity, which minimizes cyllinder-bore distortion under load. It's a very good combination of properties for a piston, but it's just not good enough to justify the huge cost for a 5 lb billet from which to cut each piston. We'd be talking $1,000 per piston here. Crazy expensive. And, although I'm quite aware of the dangers, most of the new cases of Berylliosis are due to improper safety precautions. It should be treated like a toxic chemical and, instead, it is treated like a nuisance. When the dust collects around the machine from insufficient air venting people just vacuum (sometimes even sweep!) up the dust without even wearing a respirator or mask! People need to treat it like spray paint or some other toxic chemical. I think the problem is that people don't perceive it as a danger since they cannot smell it and since the symptoms don't show up for years in most cases. Even just wearing a breather/filter and NOT taking your work-clothes home, would probably prevent almost any case of illness. Fortunately, Berylliosis cases are dropping greatly and there haven't been any serious new sensitizations in years. Now on to the next reply ... |
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12-29-2005, 01:08 AM | #34 | |
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This strive for rigidity is so great that Formula 1, in an effort to reduce costs for the less-well-funded teams, banned ANY material with a specific young's modulus over 40 GPa/(g/cc) because there were materials, like Beryllium/Aluminum alloys used by McLaren Mercedes, which were extremely expensive, but also extremely beneficial because of their higher Y.M.. In fact, they also banned its use in brakes because you can make the brake calipers drastically stiffer and more effective by using the expensive AlBe alloys. The other HUGE benefit of AlBe alloys, and pure Beryllium, is the comparatively low coefficient of thermal expansion. That allows you to use a piston with less than half the cold-clearance and to operate the piston through a wider range of temperatures. That's definitely a potential benefit. It's a benefit shared with Carbon/Ceramic piston technology as well ... which is also banned in F1 along with Metal Matrix Composites anywhere in the engine. |
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12-29-2005, 01:18 AM | #35 |
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Ive been waiting for this FAQ good job!
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12-29-2005, 01:21 AM | #36 | |
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As I know that you, of all people, are aware, there will still be extremely small, but seperate, crystals of aluminum and silicon forming the matrix. (unless it's an intermetallic alloy like Titanium Aluminide, where crystal structure is shared) Over extremely short distances, many of the properties of the elements themselves remain. So I would assert that, were I to guess about the changes in the matrix's properties, the added silicon acts to "soften" the reflectivity of the otherwise opaque aluminum. I don't think it will make the aluminum "translucent" to heat. Rather instead that it would allow some of the infrared photons to penetrate deeper into the matrix (longer mean free path due to translucent silicon micro-crystals) and be absorbed by the aluminum and then dissipated into the cooling system as heat instead of being reflected back into the combustion process. Absorbing, instead of reflecting, more thermal radiation might reduce the tendancy to detonate since thermal radiation plays a strong role in detonation. But I still think it was just for the wear properties and because of the comparative cheapness. (High silicon aluminum alloys have a low casting reject rate, or so say Chrysler failure analysis engineers.) -Adrian |
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02-23-2006, 08:35 PM | #37 |
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Beryllium is not that expensive or rare, speaking from my experience in molding.
We use this stuff in alloy form in every single one of our bottle molds (we have over 1K different molds about 10 cavities each). It is true that you can eventually develop Berylliosis from breathing constant Beryllium dust though, but I've never heard of anyone personally with the superior venting/closed environments of today's CNC machines (as opposed to an open Bridgeport mill) There are several superior conductive materials that we use. Moldstar 150 being the highest and MoldMax Hi-Hard (BeCu). I would think you'd want a non-conductive piston material though for turbo engines, to keep the heat in the exhaust, but what do I know? I am sure there is a point where high conductivity starts to hurt HP performance. |
02-24-2006, 02:12 AM | #38 | |||
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1) All but one of the alloys you've mentioned conduct less heat than pure, instrument grade, Beryllium. 2) Though MoldMax high-hard is twice as strong, it is almost five times heavier and conducts less than half as much heat. (104 W/m-K) 3) Moldstar 150, the most conductive of all the alloys relating to this, conducts 259 W/m-K. Instrument grade Beryllium conducts almost as much heat @ 216 W/m-K, is still almost five times lighter and almost as strong. I think it's fair to say that, in light of Beryllium's low weight, high strength, high modulus of elasticity and high thermal conductivity, Beryllium is still the material of choice for pistons. References... MoldMax and Moldstar BeCu alloys: http://www.matweb.com/search/Specifi...bassnum=NPER00 http://www.matweb.com/search/Specifi...bassnum=NPER01 http://www.matweb.com/search/Specifi...ssnum=NBUCOR31 http://www.matweb.com/search/Specifi...bassnum=NBBC17 http://www.matweb.com/search/Specifi...bassnum=NBBC19 http://www.matweb.com/search/Specifi...bassnum=NBBC18 Instrument grade Beryllium, again: http://www.matweb.com/search/Specifi...bassnum=MBEI2H -Adrian |
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07-30-2006, 04:25 PM | #39 | |
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How do I word this: I know for a fact that the majority of the time it is the piston when it comes to Hyper-U pistons. They physically cannot take the chamber pressures that are associated with high boost-high hp engines. They are good for what they are intended...but the line for not crossing is pretty clearly marked with them. You can almost tell at what point a hyper-u piston will fail (within batches...ie blown V-8 overhead cam engines)... they are good in that they have more quality control than cast but bad in that they do not have the physical strength of forged. |
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08-15-2006, 11:02 PM | #40 |
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[quote=Unabomber][size=3]Piston FAQ[/si
For the record, Cobb Tuning’s pistons start life as JE Piston forgings that are wholly CNC machined by Cobb Tuning. This is a common practice though, as many “manufacturers” use other manufacturers’ forgings as a 2000 ton forge costs millions whereas a CNC machine may be within their capital reach. In fact, JE Piston themselves are rumored to use TRW forgings. Additionally, you may find XXX’s pistons are actually pistons from one of the above manufacturers made to XXX’s specifications. This list represents true manufacturers and not resellers. Also realize these are the companies that stock Subaru specific pistons. As long as you have the correct measurements, almost any aftermarket piston manufacturer can custom make pistons to your specifications. TRW is no longer TRW FYI. In 2002 Northrop Grumman bought TRW and then sold TRW automotive and financial groups. They kept the space and technology group. Northrop didn't sell either group as a whole either it was pieced out (liquidated if you want). To my knowledge though the original plants are still manufacturing today under different ownership. I'm not sure but I don't think there are any TRW automotive parts anymore as the buyers of said assets are using a different name. Jacob |
09-25-2007, 06:45 PM | #41 |
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why 5-30 oil for breakin ??
I hear people using 10-30 all the time... |
10-23-2007, 08:41 PM | #42 |
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I have a 04 sti and this is the second time I blow my stock block! and it is always the piston # 4. is it ok to just build one with only pistons and rods?
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06-21-2008, 10:13 PM | #43 |
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Piston slap question
I have looked quite a bit over many diffrent threads and i can't really find the answer to my question. i have to say that this is a great write up by the way very useful thanks!! i just bought myself an 03 impreza wrx 2.0L turbo, i was wondering does piston slap effect this model or is it just the 2.5L motors. i have read in the other threads that apparently the piston slap problem that is occuring is in the bigger bored motors but i'm not sure. also is a slight valve tap normal?? sorry i know a little off the piston topic just figured i would throw it in. there is nothing done to the motor completly stock. thanks in advance to anyone who can answer.
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08-06-2008, 10:57 PM | #44 | |
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Quote:
by running the engine and if you motor has plug wires unplug the sparkplug wires from the coil (pack high ternimal)while listening to the suspected slap knock it ( the slap sound) should be noticeably quioter when the plug wires disconected for a second .Be carful not to get shocked with the spark i sometimes loosen the wire first then carefully pull it loose the rest of the way or use a wood stick taped to the wire .. if your motor has no wires just coils setting on the sprk plugs? you might disconect the indevidual coil primary leads 1 at a time ....................................outherwise.... ......................................... alternatly rev the engine to say 2500 rpm the remove the sprak wire one at a time if your slapping is quiter when a certain wire is disconected there you may have a proublem (slap , rist pin,rod bearing?)...dont forget to snug wires up good after doin this test .... And .....as for the valves tapping i might suggest an oil additive some will know it by the name CD2- oil treatment .. a detergent for desolving engine gum and varnish |
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08-07-2008, 07:47 PM | #45 |
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thanks
thanks i will certainly use the oil additive becuase i now know that the wrx has a tap like sound because of being a boxer motor as for the piston slap i will def try that plug wire removal thanks again.
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04-22-2009, 10:04 PM | #46 |
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I am at true awe at Unabombers informative posts...I feel like I know EVERYTHING after reading them. I've been to many automotive forums in my years, and none have as much information, so well organized, by ONE person.
The second best board MIGHT be VWvortex but they still don't have the amount of tech NASIOC has. |
05-09-2009, 04:15 PM | #47 |
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Hello. I'd like your opinion about what kind of pistons to use.
I'm getting a new short block and i want only drop in pistons. Untill now, i'd had race pistal pistons, but i'm using new short block because of big oil consumption. The car is 450-460 hp, with amr-t50r turbo. What about mahle pistons? A friend of mine here in Greece, told me that in USA, mahle had very good resalts in subarus. Is that correct? Thank you. |
07-14-2009, 05:24 PM | #48 |
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I just talk to Customer Service at Mahle and was told the Subaru Pistons were 4032. Sucks because I have a set waiting to go in my 08 STI.
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04-23-2010, 11:22 PM | #49 |
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I have read through this whole post and am still wondering if someone had to give a rough figure where your pushing the stock rods and pistons what hp/boost range would that roughly be?
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07-30-2010, 11:46 PM | #50 |
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I have an EJ22 phase I that I would like high compression pistons (11:1-11.5:1) for. Anyone ever really done this? Am I going to have to do custom pistons?
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