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Thread: Pistons - Cast vs Forged vs Hypereutectic

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    Toymods Club Member #194 Conversion King Lambolica's Avatar
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    Default Pistons - Cast vs Forged vs Hypereutectic

    This following a queation asked of me on MSN that whilst I know a little on the subject of eutectic phase changes I'm unsure of the resulting strength of a Hypereutectic alloy Piston.

    I am asking for peoples opinions on the use of these different pistions in a street application as there appears to be a definate cost and strength benifit (from a little of the research I have done) from using them compared to using Forged pistons, however I'm pretty sure there is a question of brittleness. weather this falls in the realm of engine conditions or not I am unsure.

    From what I gather:

    Strength:
    Cast pistons -----> Hypereutectic pistons ----> Forged pistons

    Cost:
    Cast pistons -----> Hypereutectic pistons ---->Daylight ------> Forged pistons

    Hypereutectic pistons also have a lower expansion coeffcient than Cast pistons due to higher silicone content over Cast pistons thus closer tollerences can be achieved.

    Thorghts Comments????

    Research Update
    From some searching on the net I have found further details. there is a general concensis that the strength of the pistons as I have shown above is correct however there are a few mentions of hypereutectic pistons having higher yield and fatiuge strength however the brittleness off sets this.

    Looking at what I have found I will write this pros and cos style for each type of piston.

    Cast:
    Cast pistons origonally were made form mild steel however modern pistons use alloys with an approx silicone content of 4-6% (eutectic pistons) but are cast in a similar fastion

    Molten material is poured into a mould and cooled slowly to get a fine crystalline structue as the molten mateial solitifies. forming a tight structure of the material.

    Inherant properties of the casting means that the cast pistons don't thremally expand as much as Forged and piston/cylinder wall tolerance are tighter. there is also less noise during warm up and the benifits of less blow by etc.

    Cast pistons are not good at handling severe detonation and hi temp engines (turbo, supercharged, Nitros) consensus says ~ 5-7 psi max

    The process is inexpensive than forged thus suit mass production.

    Hyper-Eutectic Pistons
    Cast in the same fashion as Cast pistons however the silicone content is higher 12.5-16%
    The casting must be done correctly in correct conditions (inert gas environment) to ensure supersaturation of silicone evenly through the structure to avoid voids.

    Are harder (and thus more brittle) than cast pistons, and are generally regarded as being better than cast due to higher heat resistance (~30% higher)

    Are suited to perfomance application where things don't excesivly heat the pistons (Turbo max boost 15psi, Nitros 100hp shot max, Compression 11:1 max) meaning a good upgrade for N/A applications of mild S/C, Turbo applications

    Cost is only a little higher that cast

    tighter tolerance advantages similar to cast.

    Both Cast and Hyper-Eutectic pistons offer weight saving advantages over (most) forged pistons as forged pistons require a larger collar for structural rigidity (Conflicting information here more research required)

    UPDATED RESEARCH
    Hyper-Eutectic pistons can be treated further (T-6 Treatment) to lift the strength by approx 30%, this is done but heating then quenching the piston in flowing water and then artifically aging the alloy buy heating it to a definete temperature for several hours and cooling in air. This form of Tempering relieves the internal stress caused by the quenching in the first stage of treatment.

    Forged
    the process of forging is basically getting a block of matrial and bealting the crap out of it in a mould before machine finishing. this results in the origonal blocks crystalline structure being bent as the piston takes shape and the fine structure flows around corners adding structural strength.

    Heat dissipation is increased due to the shape and size of the crystalline stucture. meaning pistons run cooler

    Are generally more resilliant to detonation (however you can break them still)

    Generally need greater wall top piston clearances. thus are more noisy during warm up periods. also less effecient in blow by.

    Formed from one of a number of metal alloys, including 4032 and 2618

    4032 grade usually results in tighter piston-to-wall clearances, while 2618 makes for greater piston-to-wall clearances because of its composition (higher copper content and less than one percent silicone

    Pistons formed using 2618 grade are often recommended for applications which generate increased heat and pressure. Examples of such applications include those which utilize a supercharger, turbocharger, or nitrous oxide.


    The process used to make these types of pistons is generally more expensive, and usually, forged pistons are the most costly of the piston types


    So in conclusion

    Cast OEM pistons are suitable for low temp (sub 11:1 compression ratios, N/A engines

    Hyper-Eutectic Pistons are a suitable replacement for OEM Cast and offer an exellent bang for buck for N/A engines of Factory Turbo engines that run lower Boost levels <15 psi and Will handle a Nitros shot of < 100hp

    Hyper-Eutectic pistons (T-6 treated) More research to be done however may make them more suitable for moderate boost levels. pending what happens to the brittleness.

    Forged - Still for uber boost or where hi temps are place on the piston.


    A eutectic or eutectic mixture is a mixture of two or more elements which has a lower melting point than any of its constituents. The proper ratios of components to obtain a eutectic alloy is identified by the eutectic point on a phase diagram.
    Last edited by Lambolica; 02-02-2006 at 04:51 PM.
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  2. #2
    MR 18RG Chief Engine Builder The Witzl's Avatar
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    Default Re: Pistons - Cast vs Forged vs Hypereutectic

    good topic.... there was a VERY big discussion about all this on the old forums in threads regarding the 4a-gze pistons.

    I'll try to dig up some links.... Oldcorollas will love it.
    ...... butt scratcher?!


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    Current UZA80 owner Chief Engine Builder JustCallMeOrlando's Avatar
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    Default Re: Pistons - Cast vs Forged vs Hypereutectic

    *Sits down to listen*
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    Toymods Club Member #194 Conversion King Lambolica's Avatar
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    Default Re: Pistons - Cast vs Forged vs Hypereutectic

    Yes I must state that I was am looking for Stu's input here.

    I am aware that cast pistons are eutectic, but from what I recall Hypereutectic is a different form of treatment resulting in a harder surface structure (however if I recall more brittle) It appears that a T-6 treatment is commonly used as annealing (if this is the correct terminology) to reduce the brittleness. (tempering if you will, once again my memory fails me)
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    Junior Member Too Much Toyota oldcorollas's Avatar
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    Default Re: Pistons - Cast vs Forged vs Hypereutectic

    uuh, gimme a few days
    i've only been thinking of rhenium and platinum elecroplating, and chromium and aluminium pack cementation for a while..
    and it just started snowing 20cm in the last hour!! i'm so goin skiing this weekend....

    will update post with relevant facts later

    edit: good research do i even need to add anything here?

    perhaps you could look at semi-solid formed pistons also..

    and as far as forged and thermal expansion etc, iirc, with cast you can design consitent thermal expansion into the piston, but with forged, it is more dificult to control the overall shange in shape of piston due to the limitations of geometry of forging.

    oh and eutectic is as you desrcibe, nothing to do with softening. it is just the point at which a single composition phase will form directly from a molten mixture, ie it freezes at a fixed single temperature, not over a range of temperatures

    for hypereutectic piston since there is more than eutectic silicon, when cooling the first phase to form will be rich in silicon, and then as it cools, the silicon content of the solidifying material decreases until the last bit is eutectic...
    Last edited by oldcorollas; 02-02-2006 at 01:27 PM.
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    Toymods Club Member #194 Conversion King Lambolica's Avatar
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    Default Re: Pistons - Cast vs Forged vs Hypereutectic

    Load of help you are.....
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    Junior Member Domestic Engineer myne's Avatar
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    Default Re: Pistons - Cast vs Forged vs Hypereutectic

    Hyper-eutectic?
    In soldering eutectic refers to a solder that has no plastic phase. It melts and cools directly from a solid to a liquid at a precise temperature.
    Could this mean that the hypereutectic pistons dont soften at all? Would it be why they're supposed to have minimal expansion?

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    Toymods Club Member #194 Conversion King Lambolica's Avatar
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    Default Re: Pistons - Cast vs Forged vs Hypereutectic

    Intitial post revised now I have done some Googling....
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    Former User Conversion King Joshstix's Avatar
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    Default Re: Pistons - Cast vs Forged vs Hypereutectic

    Eutectic is about saturation of the alloying agent in the solution as far as I know.

    i.e
    Hypo-Eutectic <100% saturated
    Eutectic =100% saturated
    Hyper Eutectic >100% saturated

    In this context it is discussing the amount of silicon in the alloy.

    One other advantage of the Hyper Eutectic piston is that they are more resistant to wear as there will be pure silicon on the surface of the piston and ring lands etc which is a lot harder and resistant to wear than the rest of the piston.

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    Toymods Club Member #194 Conversion King Lambolica's Avatar
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    Default Re: Pistons - Cast vs Forged vs Hypereutectic

    Correct...
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    jetpilot Automotive Encyclopaedia 1JZ.747's Avatar
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    Default Re: Pistons - Cast vs Forged vs Hypereutectic

    great post, there will be a rep point coming your way, not that you need more.

    only thing i would say is, i have factory pistons which would be cast items.


    i am running consistantly 14 psi on the street with the big turbo on street fuel. with the twins i ran 17 psi all day every day.

    on the track and dyno tuning i run 121 octane fuel and N20 40 shot of. now my boost recall has seen as much as 30 psi logged though it is set to boost spike to get it on boost faster it runs 22 psi now i am upto over 150 dyno runs and 80 passes on a race track and at times at extreme heat. ie intake temps 60 deg cel or more, my engine has done 187000 k's now.

    so in my personal experience i have found some of the info not to be correlating to my personal exepriences.

    its all very interesting, as i am at the point of deciding what to do next which a built engine is an option using forged pistons.

    Shane

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    Toymods Club Member #194 Conversion King Lambolica's Avatar
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    Default Re: Pistons - Cast vs Forged vs Hypereutectic

    Thanks for that input Shane..... I think alot of what is written is in relation to detonation as opposed to heat. If you car is well tuned you really probably only have wear to worry about.
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    Toymods Club Member #194 Conversion King Lambolica's Avatar
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    Default Re: Pistons - Cast vs Forged vs Hypereutectic

    Updated at the top also.....

    Hyper-Eutectic pistons can be treated further (T-6 Treatment) to lift the strength by approx 30%, this is done but heating then quenching the piston in flowing water and then artifically aging the alloy buy heating it to a definete temperature for several hours and cooling in air. This form of Tempering relieves the internal stress caused by the quenching in the first stage of treatment.
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    ethanol sniffing Backyard Mechanic adamaw11's Avatar
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    Default Re: Pistons - Cast vs Forged vs Hypereutectic

    Cast OEM pistons are suitable for low temp (sub 11:1 compression ratios, N/A engines)

    can anyone comment on the pistons in the 20v blacktop? They are cast OEM pistons aren't they? and the compression ratio IS 11:1 so are you saying its right on the limit with these pistons?

  15. #15
    Toymods Club Member #194 Conversion King Lambolica's Avatar
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    Default Re: Pistons - Cast vs Forged vs Hypereutectic

    I think when they say that, they are talking about 11:1 when tuned to within an inch of it's life.

    Toyotas generally run rich everywhere as a precation against detonation.

    I believe the 20v pistons would be a Cast eutectic alloy not mild steel cast.
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