Is there anyone that has tried a nitrous direct port system on their STi? What is the best system to buy? What other feedback should I know before installing and using? Any help would be appreciatted.

I heard the USDM STi pistons were umm... hypereutectic cast, which utilizes a higher content of silicone and supposeldy hold up just as well as forged pistons, but are not prone to the thermal expansion problems that forged pistons are.

"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. The high silicon content of the aluminum also has the benefit of providing exceptional scuff resistance and reduced thermal expansion which allows for the use of tighter clearances."

however, pistons using this type of casting are said to be very weak to detonation as well as frequencies generated by NOS... so it's your call... anyone have any input on this?

BTW... "stronger" is relative to what variable you're measuring... just check out the USDM vs JDM piston threads and I'm sure you can find info about it... or google "hypereutectic" and you should be able to find something about NOS compatabilities since NOS subjects the engine to similar stresses as detonation does.

"A.Graham Bell in his recent book "Forced Induction Performance Tuning" (published in 2002 by Haynes) says they are a poor choice for turbocharged engines. Hypereutectic cast pistons have about twice as much silicon in the aluminum alloy as regular cast pistons (15-20% instead of only 7-8%). According to Bell, the added silicon leaves them "quite brittle and, as such, prone to breaking when subjected to detonation."" - bad for turbocharged engines IF you get detonation that is...

more info on technicalities of hypereutectic iron
http://members.lycos.nl/cvdv/hypereutectic.htm

"higher silicon content in the Hypereutectic alloy lends itself to improved scuff resistance and, importantly, a relatively low expansion rate"

as we all know standard cast pistone whether hypoeutectic or Eutectic, already expends much less than forged metals due to their internal metal structures... tighter tolerances also allows for better emmissions due to increased efficiency, so maybe this is why Subaru chose thos route instead of the forged route? hmmm interesting...