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Thread: Hypereutectic pistons in a jet boat

  1. #1
    Blown 472
    any experience wif them? good or bad??

  2. #2
    Yes, KB hypers in a challenger type jet. No problems yet, but not a lot of use so far. I think the problems are all associated with the top ring gap. Seems like they gotta be loose..........See the manuf. ring gap instructions........MP

  3. #3
    Check out his link from a previous post and this will tell you everything you want to know...

  4. #4
    I posted this in the previous post mentioned above. Hope it sheds some light.
    Ask the kid on the street what performance is and he'll raise the hood of his Honda. Ask the Funny Car drag racer about performance and he'll take you to the starting line to breathe the nitromethane. Ask the mother on vacation and she'll tell you about driving to California from Indiana pulling a car BEHIND the motorhome through the Rockies in the western United States.
    Ask about selecting the proper piston for each of these applications and you'll probably receive just as many different answers.
    While the basic operation of an internal combustion engine hasn't changed significantly in more than 100 years, the uses (and misuses) of said engine certainly have - especially with regard to high performance applications. Piston manufacturers in particular say that while today's performance choices are exciting, they also mean selecting a piston is a challenging task. Just as you can't paint the performance picture with a broad brush, piston selection criteria have become so challenging - yet so important - that many engine builders are understandably confused by the options.
    "In addition to our forged products, we offer a variety of pistons designed to meet a customer's needs and his wallet," says KB Pistons' Sulprizio. "Sometimes a claimer engine just needs a reasonable product at a reasonable price that does what it's supposed to do."
    Federal-Mogul's Hayes says that if you're trying to use these high output small engines with substantial nitrous under the hood of a sport compact car, forged pistons are probably your best bet. Federal Mogul is developing a line of upper-end performance forgings that will also include import engines. However, he says don't count out hypereutectic pistons when they're appropriate. Years ago, when NASCAR ran open class engines, we tested some hypereutectic pistons in 750 hp engines running around 8,300 rpms," Hayes recalls. "The pistons gave some definite advantages over some of the best forgings used at the time, including high heat strength, better endurance, no scuffing. We probably came away with 22-25 more hp due to the lighter weight and tighter bore clearances. We could have installed thinner ring packs, which would further reduce weight and friction. Overall this means less blow-by, more efficiency, and thus more horsepower."
    Cast? Hyper? Forged?
    The alloy from which a piston is made not only determines its strength and wear characteristics, but also its thermal expansion characteristics. Hotter engines require more stable alloys to maintain close tolerances without scuffing.
    Many pistons used to be made from "hypoeutectic" aluminum alloys like SAE 332 which contains 8-1/2 to 10-1/2 percent silicone. Today we see more "eutectic" alloy pistons which have 11 to 12 percent silicone, and "hypereutectic" alloys that have 12-1/2 to over 16 percent silicone.
    Silicone improves high heat strength and reduces the coefficient of expansion so tighter tolerances can be held as temperatures change. Hypereutectic pistons have a coefficient of thermal expansion that is about 15 percent less than that for standard F-132 alloy pistons. Because of this, the pistons can be installed with a much tighter fit - up to .0005? less clearance may be needed depending on the application.
    Hypereutectic alloys are also slightly lighter (about 2 percent) than standard alloys. But the castings are often made thinner because the alloy is stronger, resulting in a net reduction of up to 10 percent in the piston's total weight. Hypereutectic alloys are more difficult to cast because the silicon must be kept evenly dispersed throughout the aluminum as the metal cools. Particle size must also be carefully controlled so the piston does not become brittle or develop hard spots making it difficult to machine. Some pistons also receive a special heat treatment to further modify and improve the grain structure for added strength and durability. A "T-6" heat treatment, which is often used on performance pistons, increases strength up to 30 percent.
    Machining hypereutectic pistons is also more difficult because of the harder alloy. Consequently, hypereutectic pistons typically cost several dollars more than standard alloy pistons. That's why most OEMs (except Ford) have gone back to eutectic alloy pistons in their late model engines. High copper eutectic alloys offer most of the advantages of hypereutectic alloys without as much cost.
    Forged pistons will generally come from one of two aluminum alloys: SAE 4032 and 2618. A 4032 alloy is high silicon and usually used in naturally aspirated engines, while a 2618 alloy is a low silicon material designed for the abuse of marine, supercharged and nitrous applications. A 2618 alloy is about 3 percent heavier and doesn't have as good lubricity qualities as the 4032 because of the lower silicon content. A 2618 alloy will also expand more than 4032 because of the denser material. Because of this difference in expansion, the manufacturer will design the necessary clearances into the piston; the engine builder will not normally need to change recommended running clearances.
    The 4032 composition will be what you find in virtually all circle track-type applications as well as street applications in which a forged piston is desired. The 4032 can be made as strong as 2618; it would just need to be thicker. The melting point of these alloys is about the same, so that wouldn't be a consideration.
    The most important factor in piston choice is application. What do you need the piston to do? Street and drag race applications are easy on pistons, circle track and road race applications are somewhat tougher, while marine, supercharged and nitrous engine applications will produce the toughest environments.
    A related factor to consider is how often do you want to inspect and/or change the pistons? Do you want the pistons to last a full season or even several seasons? Or do you want the lightest pistons possible and plan to change them after every few races?

  5. #5
    Blown 472
    Interesting, thanks Steel

  6. #6
    Ran Them In My Last Two Blower Motors Love Them!keith Black 496
    12-71 Blower Pump Gas No Problems!

  7. #7
    Thanks everyone , I am just now buying some pistons for a 454 and this thread has really made it easier. :coffeycup :coffeycup v-drive

  8. #8
    Anyone else here besides me notice that of all the hyperuteuctic pistons noted crumbling in our motors, it's always a brand other than Keith Black? The KB's seem to take the abuse.
    Also, when I made a statement about not using hypers in a motor we are building for my hydro, my partner was perplexed. "Why not," he asked, "I've put 'em in dozens of circle track motors that run sustained R's all day long." I went on to complete my statement, saying that all the brands of hypereutectic's turn to gravel in the bottom of our pans except for the Keith Blacks. He confirmed that the hypers he was using in these high rpm screamer circle track engines were also KB's and holding up to the abuse.
    I'd trust the KB's in a little ol' jet boat, but not so sure about the other brands...

  9. #9
    has anyone had any experience with "Silv-o-lite" hypers? ive got a genV that has already been machined for them and ready for install. it was going to go in a truck but now want to use the engine for a 20' cruiser (jet). should i be worried?

  10. #10
    has anyone had any experience with "Silv-o-lite" hypers? ive got a genV that has already been machined for them and ready for install. it was going to go in a truck but now want to use the engine for a 20' cruiser (jet). should i be worried?
    Silvolites are indeed a KB product, but I don't think they are much of a performance piston. They are more of an oem rebuilder piston/stock application. I don't think putting those in a jet boat is a good idea. ( opinion.)
    Hypers usually install pretty tight in the bore, so finding a forged set of pistons and honing out your holes may be an option. Or look at KB's performance line-up of pistons for the chevy...I've never cross-referenced, but maybe the KB bore specs are similar to the KB Silvolites bore specs (piston should be of much better material than the Silvolites).

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