Myth Busting the 02-05 STi Pistons
 

Its time to find out once and for all what type of Pistons are used in the Aus Road Spec 02-05 STI's. Open, semi or fully closed block would be good info whilst we are at it.

Lets avoid hearsay and assumptions if we can so please include the source of any info. Stace can you provide a link to the engine numbers? It seems anytime an STI bottom end pops up with forged pistons and a semi closed deck it is immediately assumed it must be an 02...

Recapping, how did we get here? Subaru Marketing (unconfirmed source in my book) said the 02-05 STI's had the Hyperutectic Pistons. Then local workshops find real Forged Pistons in the Aus 02 STI's. Hence the Myth is born.

Any volunteers for a team of "Block Busters" to visit John Keating at Regents and inspect the pistons his Blocks have. Not conclusive but additional info. Has anyone cracked an 03-05 STI ?

Has this matter been discussed on other forums, if so what was the key finding?

Problem though, are the blocks that John Keating has JDM 02 STi blocks? The only way to get real answers is to find someone who has done an engine in an 02, 03, 04 and 05 STi and do some detective work when the engine gets torn down.

I can 100% confirm semi closed deck in the Aus delivered 02 STI motors. Al's short motor is in my car. Had a good look at it before it went in. Is definately semi closed deck.

Re pistons, I cant confirm forgies.

and dont forget subaru have been known to use their 'special parts bin' pretty much putting whatever they want into their cars even if it's not the same as the next car in the production line

[URL]http://forums.nasioc.com/forums/showthread.php?p=10671156#post10671156[/URL]

give this a spin :)

pretty much has everything

[QUOTE='[PFFT]']and dont forget subaru have been known to use their 'special parts bin' pretty much putting whatever they want into their cars even if it's not the same as the next car in the production line[/QUOTE]

Yep, my STi RA Spec C MAP sensor proves this....it caused tuning problems with my Link AND Motec, and Motec confirmed with a diagram that my sensor was a variation fitted to some JDM Spec C models.

I asked Michael South for his expert opinion and he had this to say:

Hi,
The 02-05 is the same base engine, built for export market from FHI, it uses the 02 STI JDM spec full forged pistons, which have a wide flat plane across the crown above the pin hole. All STI blocks made after and including 01 are semi close deck, including JDM spec which has the hyper crap pressure cast pistons as of MY03. No 2.0lts AU spec STI has these hyper crap pressure cast pistons.

The hyper pistons have a round crown fully turned, no milled tops apart from valve relief’s.

I have had 02 -05 engines apart, not much has changed, although there are different part numbers for the blocks, you need to have 2 side by side to see any difference.

The big issue comes from the hyper pistons in that they are pressure cast, this has seem to be lost in translation where they think the 2.5sti has forged, which they are not, but the piston in the 2.0lt AU spec STI are a true forged pistons.
Cheers

Michael



MSR Rally Team

[url]http://www.users.bigpond.net.au/msgofast/index.html[/url]

^^^^^ Seems to agree with what I had heard. Nice to hear it from someone who has had a few of them apart and seems to know what he is looking at when he does.

Here we go, more thanks to Michael South for these pictures:

02-05 Aus Sti with Semi Closed Block and Real forged pistons
[IMG]http://i31.photobucket.com/albums/c379/my99maddog/02Forged.jpg[/IMG]

Now those Hyper Crappy Pistons found in the Jap Specs
[IMG]http://i31.photobucket.com/albums/c379/my99maddog/Hypercrappypiston.jpg[/IMG]

This myth is now totally busted.

Thanks for that - clears up a few questions for me :)