FUEL STORAGE:
Shell USA
As gasoline ages in the presence of air, chemical changes may occur because certain fuel components will slowly oxidize. These chemical changes contribute to existent gum (discussed above). This oxidation process may be slowed by adding inhibitor additives to the fuel.
The ASTM specification has an oxidation stability test that predicts the ability of the fuel to resist gum formation when stored. However, gasoline does have a finite storage life, because gum formation cannot be completely eliminated. Normally gasoline will be good for about six months, but predicting storage life is difficult, because storage conditions vary greatly. Gasoline is usually consumed shortly after manufacture, so storage life is of little consequence to most consumers.
When gasoline is stored for longer than six months, or when storage conditions are not favorable, monitoring existent gum content may be necessary to make sure the stored gasoline will perform when used. Reformulated gasoline’s and other oxygenated gasoline’s have storage lives similar to conventional gasolines.
Unocal 76
"light ends" evaporate in the intake manifold during a cold start thereby providing vapors The manner in which racing gasoline is stored is very important if you want to have the same quality product after storage that you had prior to storage. This can be just as important for your lawn mower gasoline as it is for the gasoline you use in your racecar. If the proper storage procedures are not used, some of the "light ends" (hydrocarbons that boil at ambient temperatures) can be lost when the storage container is opened. to the combustion chamber for ease of starting. Even more important, the loss of these "light ends" can contribute to lost octane quality and reduced power, which can be detrimental in racing. These problems can be minimized by following a few general rules.
1. Store racing gasoline in a cool place.
2. Store racing gasoline in steel 55-gallon drums or steel 5-gallon cans with tightly sealed caps. This does not include most plastic jugs since their sealing ability will not contain the vapors of gasoline. Some plastic jugs allow the gasoline to be exposed to sunlight, which deteriorates the tetraethyl lead in the gasoline, which in turn reduces the octane numbers.
3. If your storage container is warm or hot, put it in the shade to cool down before opening it. This will help to retain the "light ends".
4. 76 Racing Gasoline has a longer shelf life than street gasoline due to lower levels of olefins and higher levels of additives to resist gum formation. Storage for two years in a cool place in tightly sealed containers is not a problem.
VP Racing Gasoline
As long as the gasoline is kept in a tightly sealed container, the storage is indefinite. These gasolines contain olefinic hydroccarbons in negligible concentrations, thus their tendency to form gums and varnishes is negligible. The gasoline will not separate, as its components are solvents of each other. Also, don't expose the fuel to direct sunlight, as the ultraviolet rays will oxidize the lead.
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CAST AND FORGED PISTONS
The majority of original equipment and aftermarket pistons are manufactured through casting. The technical description is 'gravity die casting'. However for the sake of simplicity, a cast piston is manufactured by pouring molten aluminum/silicon alloy into a mold. Forged pistons differ fundamentally in manufacturing and inherent character. As opposed to casting the forging process basically takes a lump of billet alloy and stamps the shape of the piston from a die. Of course, both manufacturing procedures are a lot more complex and intensive that this simple analysis but you get the broad picture.
Casting and forging results in two different types of piston. A die for forged piston must be designed so it can easily be removed and, as a result, the forged blank (or unfinished piston) has a relative simple shape. Casting can achieve a more complex blank, therefore, facilitate lightweight construction. Also, due to relative manufacturing procedures forged pistons tend to be more expensive than cast. Custom made pistons come with a heafty price tag.
CAST PISTON MATERIALS
No matter which piston you use and no matter which engine a piston goes into they are all made from a combination of both aluminum and silicon. It is the amount of silicon though, which determines the pistons overall strength verses wear resistance properties. Silicon also controls the rate of expansion of the piston as the material becomes hotter (the less expansion then better!). Silicon content also markedly affects actual material hardness. More Silicon makes the piston much easier to machine-in the manufacturing phase. There are traces of many other metals in cast pistons, including copper, nickel, manganese and magnesium, all of these adding somewhat to the overall behavior and strength of the piston.
HYPEREUTECTIC AND EUTECTIC
Pretty much the catch words in cast pistons towards the end of last decade, Hypoeutectic, Eutectic, and Hypereutectic are metallurgical terms which describe little more than the amount of silicon present in the piston material and the way in which it is structured (uniformly) in the piston itself. Hypoeutectic describes a molten mixture of alloy, which contains a low quantity (up to around 10 %) of silicon to aluminum ratio where the silicon can completely dissolve. Manufactures don't use hypoeutectic alloy much for cast piston construction, so this is the last we'll mention of it.
The term Eutectic means that the piston contains around 12.5% silicon. This is just about the point of total dissolved silicon saturation. A great example of this that most everyone can relate to is stirring sugar into your ice-tea, the fluid will only accept so much sugar the rest ends up in the bottom of the glass. Hypereutectic alloy is pretty damn similar to Eutectic but has a much higher degree of silicon in its makeup something around the 16-18 % mark. What this actually achieves in the piston-manufacturing process is a high degree of free (un-dissolved) silicon in the end piston. The silicon/aluminum ratio affects the metal's character. The higher silicon content in the hypereutectic alloy lends itself to improved scuff resistance and most importantly a relatively low expansion rate. Aftermarket forged-piston manufactures have caught on and are now offering high silicon content alloy pistons.
With Hypereutectic pistons the primary reason for having all of this free silicon is to reduce piston ring groove wear. This allows piston designers to move the top compression ring much farther up the side of the piston (where combustion temperatures are much hotter) the enable them to run much smaller and thinner piston ring lands (the metal section separating the ring grooves). The reason piston designers want to do this is that it allows a lighter piston to be produced. If higher piston strength is needed then generally a piston manufacturer will asked for more copper and nickel to be added to the alloy for extra high temperature strength.
CAST VERSES FORGED
This is an age-old problem for engine designers. At what sort of power level is it necessary to change from a conventional cast Eutectic/Hypereutectic piston to a forged item? According to piston engineers the only real disadvantage of a cast piston (in high output situations) is in the case of a piston failure a cast piston is more likely to shatter and damage the whole engine.
A big advantage with forged pistons is they generally result in a more ductile material with the effect being the piston can take a higher level of detonation before failing. In extremely high rpm/high horsepower applications, the great strength of the forged piston can add reliability
CONCLUSION
All metallurgy aside, it is not so much what material your pistons are made from but their physical design that is will determine ultimate durability and whether they are going to break/seize. There is little advantage in investing large sums of money in forged pistons when a correctly tuned engine with standard high silicon cast pistons will give the same power output and reliability levels.
IN THE FUTURE
Ring-less pistons made of lightweight carbon/carbon composite materials. This is a logical extension of previous research that showed that engines that contain carbon/carbon pistons with conventional metal piston rings running in conventional metal cylinders perform better than do engines with conventional aluminum-alloy pistons. The observed performance improvement (measured as increased piston life during high-performance operation) can be attributed mainly to the low thermal expansion of the carbon-carbon composite. Carbon-carbon pistons can continue to operate under thermal loads that cause aluminum pistons to seize or sustain damage due to excessive thermal growth and thermal distortion.
In addition to having an extremely low coefficient of thermal expansion, carbon-carbon is about 30 percent lighter than aluminum, which provides the benefit of reduced reciprocating mass (lower reciprocating mass can potentially reduce vibration forces and increase r/min. capability). Carbon-carbon composite also has the advantage over aluminum that it fully retains room-temperature strength and stiffness at high temperatures. Further more, the strength, thermal expansion, and thermal conductivity of carbon-carbon composites can be tailored by orientation of the carbon fibers and selection of fiber type, matrix type, and processing methods.
