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Old 11-13-2003, 10:39 PM   #1
verc
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Default So subaru claims it's cast pistons in the STi are stronger than forged...

"NOTE: Our 40 yrs. experience has shown us that these pistons should never be used with Nitrous, super charger or turbo's. A forged piston is recommended in these applications, remember hypereurectic pistons are still cast pistons. "

LOL
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Old 11-13-2003, 10:59 PM   #2
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Where is your cut and paste from?

What material piston are they talking about?

Have they tested the UAC12H piston material?
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Old 11-13-2003, 11:24 PM   #3
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eh I just cut and pasted this on a whim.

They are from KB racing's site.

I actually don't know jack about the 2.5l block except that they use hypereurectic cast pistons. And from my understanding of what hypereurectic means, the STi pistons are nevertheless high in silicon content. And My expertise is in forging and machining, so I don't know jack about casting parts and methods for making them strong what not either

Curious, What is this UAC12H piston material we have?
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Old 11-14-2003, 01:01 AM   #4
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T6
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Old 11-14-2003, 01:08 AM   #5
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Poor Supra's have cast pistons. 1000HP they musn't be any good.
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Old 11-14-2003, 01:48 AM   #6
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Quote:
Originally posted by Wombat North
Poor Supra's have cast pistons. 1000HP they musn't be any good.

... :wl sounds:: ....
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Old 11-14-2003, 09:21 AM   #7
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It means they are stiffer, and stronger (than the normal sti forged ones) at low operating temps. At high temps, things aren't as good though.

Paul
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Old 11-14-2003, 09:44 AM   #8
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Subaru's loling too. Early this year some WRC commentators were suggesting that Subaru made a mistake by switching to cast pistons for their rally car. That was before they won 4 of the last eight rallies of course.


"This latest STi piston is a departure from previous years in that it is a cast aluminum design. However, we believe this to be a special hypereutectic material and STi claims a 120% increase in strength over their previous forged pistons. "

http://www.rallispec.com/product-eng_1.htm
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Old 11-14-2003, 09:55 AM   #9
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You should do a search, this is like the 3rd time for this conversation. You'll also notice there aren't a bunch of STi's with melted pistons either.
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Old 11-14-2003, 10:07 AM   #10
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Many ford/chevrolet guys out there run hypereurectic pistons with 100-150 shot of nitrous and have make hundreds of passes with out issue.

FWIK Hypereurectic have come a long way. Subaru most likely chose to use them over forged as the production process is cheaper, there is less waste and production failure (% bad off the line) on hypereurectic pistons is much less them forged. They are also stonger then the WRX cast pistons which when properly tuned have held up to more power then I will ever put down.
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Old 11-14-2003, 10:10 AM   #11
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Eutectic is a material science term that means that the elements combined (Say AL-Zn-NI-Mg-Cu ) are combined in proportions to give the lowest possible melting point. It also means that the mixture behaves as a single element. The mixture has a sharp melting point, and the melting point is the same as the freezing point, there's no hysterisis there.

If the STi engine can hold as much torque/HP as 6-speed, no need to worry IMO. How many of us are ever going to see torque/HP levels above 450/450?
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Old 11-14-2003, 10:24 AM   #12
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Hypereurectic cast pistons will also expand less, since they are typically less dense than forged pistons. That means that the engine can be set up with tighter (cold) piston/cylinder clearances. With forged pistons, they typically slap a bit when cold, while warming up, and that can potentially reduce the life of the engine, especially in the hands of "consumers" who may not be as diligent as they could be when warming up the engine at initial startup, especially in cold climates. My 2 cents worth.
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Old 11-14-2003, 10:55 AM   #13
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Default well. almost

Quote:
Originally posted by bcblues
Hypereurectic cast pistons will also expand less, since they are typically less dense than forged pistons. That means that the engine can be set up with tighter (cold) piston/cylinder clearances. With forged pistons, they typically slap a bit when cold, while warming up, and that can potentially reduce the life of the engine, especially in the hands of "consumers" who may not be as diligent as they could be when warming up the engine at initial startup, especially in cold climates. My 2 cents worth.
when the right forgeed pistons are properly sleeved and matchedto the cylinders, this is not an issue with 5 minute cold weather warm up.
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Old 11-14-2003, 11:09 AM   #14
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And when they are sized so that they do not slap when cold... they tend to expand and seise to the bore when running high HP for a long time... like road racing with a decent sized turbo.
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Old 11-14-2003, 12:34 PM   #15
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sorry for openning this can of worms.
I was kind of high one night made a random post.
Now We're getting into a lot of redundant beat over info.

Mod please lock this thread.
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Old 11-14-2003, 01:42 PM   #16
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well, some of the n00bs havent seen this before (like me) and it's not something I would ordinarily search for. Of course, now I'm off to hit the search function ...
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