Sorry if this is a re-post

http://www.subaru.net/models/2006/impreza/intro/WRX-STi_intro.htm

I doubt it, looks like the same garbage subaru provided when the 04 sti came out.

SOA has always said the STi has forged pistons. Here's their press release announcing the 2004 STi:
http://vocuspr.vocus.com/VocusPR30/DotNet/Newsroom/ViewAttachment.aspx?SiteName=Subaru&Entity=PRAsset&AttachmentType=F&EntityID=58211&AttachmentID=d1765488-9612-47ed-b7ae-af3e19e13d68

Looks like the same nonsense they claimed for the MY04 STi. I'd be surprised if they swapped back to forged at this point. I thought even the JDM version of the STi lacked forged pistons. Why would they change back to forged for the USDM? For stock boost and power level, the cast are fine and actually probably run smoother than most forged would run (piston slap in cold startups...).

Still don't understand why they advertise forged pistons though? :confused:

I thought that hyper was a method of forging. I have no idea, but I spoke to the SOA rep when I went to the C&D/Solberg event at Indy Raceway Park.

He said that the '06 pistons were Forged and they were the same as they have been since the onset of the US STi.

I thought that hyper was a method of forging. I have no idea, but I spoke to the SOA rep when I went to the C&D/Solberg event at Indy Raceway Park.

He said that the '06 pistons were Forged and they were the same as they have been since the onset of the US STi.
I don't think hyper is the same as forged. Hyper is more prone to failure under higher power levels + detonation situations. If they claim hyper is the same as forging then that would explain why they keep advertising the fact that they have forged pistons in the STi...

hyper is still a casting method. hypereutectic (sp?) just means more silicon doping right?

hyper is still a casting method?

Yes. Forging is quite different.

I don't think hyper is the same as forged. Hyper is more prone to failure under higher power levels + detonation situations. If they claim hyper is the same as forging then that would explain why they keep advertising the fact that they have forged pistons in the STi...
I think I'm going to see if I can't kick over a few rocks and find some sort of an answer. I was basing my assumption off of the idea that hypereutectic (thx pio;)) only went towards describing the composition of the material, be it forged or cast. For all I know, there could be 30 other methods for creating from metal.

The only thing I saw after a quick search is that TRW makes something they call forged/hyper: http://www.flatlanderracing.com/trwpistons.html It seems that everybody else seems to think that hyper and forged are mutually exclusive.

I did find this thread on here: http://forums.nasioc.com/forums/showthread.php?t=465249

So is someone going to have to pull apart an 06 STI engine to make sure they are really forged?

This is the only thing holding me up from buying one...

I doubt anybody's going to bother pulling one apart. SOA has always said the pistons were forged and we have always known that they were cast. Like someone said earlier, they aren't going to change now.

The only thing I saw after a quick search is that TRW makes something they call forged/hyper: http://www.flatlanderracing.com/trwpistons.html It seems that everybody else seems to think that hyper and forged are mutually exclusive.

I did find this thread on here: http://forums.nasioc.com/forums/showthread.php?t=465249
The Forged/Hyper on that link doesn't mean Forged and Hypereutectic, they are saying Forged or Hypereutectic. If you click further in(http://www.flatlanderracing.com/trwbuick.html), you will see:

Part #'s starting with "H" = Hypereutectic
Part #'s starting with "L" = Forged
Part #'s ending in CP = Coated Piston

http://www.beckracing.com/page11.htm

http://www.diracdelta.co.uk/science/source/h/y/hypereutectic%20alloy/source.html

If anyone has a picture of a broken STi piston showing the grain of the aluminum, this debate can be quickly settled. Forged grain-structure can be seen fairly easily.

Hyper-eutectic just means more silicon content than a "normal" eutectic piston.

-Adrian

There is no debate. All STI's have cast, not forged pistons. They used to be forged before '04 [version 7's], and some of the advertisements were outdated. That's what started the pseudo controversy.

There is no debate. All STI's have cast, not forged pistons. They used to be forged before '04 [version 7's], and some of the advertisements were outdated. That's what started the pseudo controversy.


Okay. :devil:

Then they didn't bother to "update" the advertisements for 2006, either.

I'm amazed that no sports car enthusiast has sued over this...but I'm not a lawyer, and I'm sure there are disclaimers involved, i.e., "We reserve the right to make engineering revisions (flatheads left over from Ford) as FHI sees fit".

The tooling that makes the stock STI pistons is forged. Isn't that close enough?

BTW, I do not know for sure the tooling is forged, but it would seem likely.

So is someone going to have to pull apart an 06 STI engine to make sure they are really forged?

This is the only thing holding me up from buying one...

Well, since you missed it somehow.

THEY ARE NOT FORGED

word dude, word.

APS down under pulled apart USDM and JDM and showed them side by side to verify that the US are cast and JDM weren't. Pics should still be there on the APS website...

Okay....I'm a newb...
So which ones better Cast or forged... I gotta 05 STi... :p

Okay....I'm a newb...
So which ones better Cast or forged... I gotta 05 STi... :p

A forged piston is much stronger and will withstand significantly higher levels of boost

Hyper = harder (not necessarily stronger) = more brittle.

My hyper (oem):
http://gpatmac.us/SubaruPics/New_Piston/BadBad1.jpg
http://gpatmac.us/SubaruPics/New_Piston/BadBad2.jpg

Hyper = harder (not necessarily stronger) = more brittle.

My hyper (oem):
http://gpatmac.us/SubaruPics/New_Piston/BadBad1.jpg
http://gpatmac.us/SubaruPics/New_Piston/BadBad2.jpg

Yep, definitely cast. However, they appear to be a low-void pressure cast. The grain-structure just doesn't match the pressure-lines forged pistons have. Forged pistons look like they are made of layers which are perpendicular to the direction the pressure was applied.

Here's another cast piston from an N/A car I took apart not long back. You can see the aluminum grain structure is similar:

http://img.photobucket.com/albums/v14/SaabTuner/ViggenData/B212PistonBroken.jpg

-Adrian

Looks like the same nonsense they claimed for the MY04 STi. I'd be surprised if they swapped back to forged at this point. I thought even the JDM version of the STi lacked forged pistons. Why would they change back to forged for the USDM? For stock boost and power level, the cast are fine and actually probably run smoother than most forged would run (piston slap in cold startups...).

Still don't understand why they advertise forged pistons though? :confused:

False advertising :mad:

The piston part numbers for the 04-05 and the 06 are identical (12006AC390 for the standard bore, type A). They are hypereutectic, which does not expand as much as forged, but does not hold up to the ultimate power levels due to being more brittle. That being said, the stock STI blocks with these pistons have proven to handle well in excess of 400 whp (close to 500 whp in some cars) with no problems as long as the tune is good.

Hello Mr. Goins:

Thank you for your patience and for bringing this misinformation to our
attention. Here is the correct information on the pistons in all WRX STi
Sedans, from the 2004 through the 2006 models:

The pistons in all 2004 to 2006 STI vehicles are made from a lightweight
aluminum-alloy metal and manufactured using Hyperutetic, which is a high
pressure casting process. This process eliminates the micro defects in the
metal structure increasing the rigidity of the piston, especially at high
cylinder combustion temperatures. The process also stabilizes the expansion
rate of the piston improving the overall reliability.

Note: The pistons in all STI engines are not forged

The Press Release from 2004 was incorrect. Unfortunately, some of the
information from that Press Release, including the piston information, was
used again for the 2006 Press Release.

Subaru of America has corrected this information in its files and sincerely
apologizes for this situation. Again, we appreciate that you brought this
to our attention.

Sincerely,

John J. Mergen
Subaru of America, Inc.


Looks like they have fixed the misinformation finally.

Nice work!

Let me be the first to say I told you so.

Hello Mr. Goins:

The pistons in all 2004 to 2006 STI vehicles are made from a lightweight
aluminum-alloy metal and manufactured using Hyperutetic, which is a high
pressure casting process. This process eliminates the micro defects in the
metal structure increasing the rigidity of the piston, especially at high
cylinder combustion temperatures. The process also stabilizes the expansion
rate of the piston improving the overall reliability.
Sincerely,

John J. Mergen
Subaru of America, Inc.

Thanks very much, Mr Mergen.

SOA has always said the pistons were forged and we have always known that they were cast.

Sti's are forged in international spec cars. It is a Ver7 bottom end. I think they used the press material from international spec vehicles and copied and pasted. Problem is advertising and marketing firms manage those sites not the powertrain engineering staff.

Perhaps the manufacturing will get better....

That John Mergen, always setting the record straight.