32 replies to this topic

[BigWillieStyles]

hello all,

well I was under the impression that these cars didnt recieve forged internals but some discussions on the UK forums has led me to question this. Can anyone confirm what the B4/Legacy pistons were made of?

The 7500 rev limit has been suggested to be similar to that of an sti and that Subaru may have put in forged pistons to counter any negative affects related to the high rpm. Also, while not a good source, wiki also suggests that they did get forged pistons.

Anyone opened up their engine and can comment on this? Any GTB halfcuts?

thanks

Will

[Shiv]

Pretty sure the Gen2 GTB (EJ20R) had forged pistons.

[Jimbo]

Im actually not sure about the Gen2 GT-B. I have a feeling they may be cast. I know its the same as V3/4 STI but i dont think they had forgies of the STI kind. May be forged but not the same way as STI's. Gen3 B4's may be semi-forged, not 100%.

[B4TT]

They are a shitty version of forged pistons, lightweight aluminium (fr the b4)

[Evil_VZ-T]

No, They have higher compression pistons with a higher piston crown

[Soop]

Besides, Its the rods that you need to worry about at higher RPM.
Lance, whats the quench distance on a B4 motor like?

[GT_Tony]

im pretty sure (from what i've read and been told) the Gen 4 GT's came out with forged pistons

[B4TT]

No, They have higher compression pistons with a higher piston crown

It is in the tech manual as one of the features of the engine, lightweight forged aluminium molybdenum coated pistons.
I do not see why this question is still debated?

[XXB4XX]

The B4 and pistons can take a fair bit of a caning.. the big end bearing can't.. that's what we all need to be worried about here.. not wether the pistons are forged

[B4TT]

this is true... though mine was the opposite, piston and bore suffered all the damage and the big ends where fine !!

[aekOne]

^ same here.

[allpaw4]

They don't have the true forged pistons of the aftermarket quality. They have what are called hypereutectic pistons. Its basically a hybrid between full forged and cast. Have a read on wikipedia about them.

Cheers,
Ben

[B4TT]

They don't have the true forged pistons of the aftermarket quality. They have what are called hypereutectic pistons. Its basically a hybrid between full forged and cast. Have a read on wikipedia about them.

Cheers,
Ben

Sounds about right

[Soop]

They don't have the true forged pistons of the aftermarket quality. They have what are called hypereutectic pistons. Its basically a hybrid between full forged and cast. Have a read on wikipedia about them.

Cheers,
Ben

Thats incorrect. Hypeutectic pistons are still cast pistons. Its the metal content that determins whether or not they're eutectic or hypereutectic.

Its really easy to tell the difference between a cast and forged piston. With them out of the motor, stand them on end and hit the skirt with a hammer softly, A cast piston will have a high pitch ting, a forged piston will have a dull thud. This is due to the way the molecular structure of the material is changed with the different manufacturing process.

Can anyone tell me what the quench distance is for a B4 motor?
Or I can work it out myself is someone can quote me the deck height and standard gasket crush height.

If no one knows the deck height, can anyone quote me: Stroke, rod length and combustion height. And I will work it out from there. (Combustion height is from the middle of the pin to the top of the combustion surface)

[XXB4XX]

Thats incorrect. Hypeutectic pistons are still cast pistons. Its the metal content that determins whether or not they're eutectic or hypereutectic.

Its really easy to tell the difference between a cast and forged piston. With them out of the motor, stand them on end and hit the skirt with a hammer softly, A cast piston will have a high pitch ting, a forged piston will have a dull thud. This is due to the way the molecular structure of the material is changed with the different manufacturing process.

Can anyone tell me what the quench distance is for a B4 motor?
Or I can work it out myself is someone can quote me the deck height and standard gasket crush height.

What the hell is quench distance?

[Soop]

Quench distance is the gap between the combustion surface and the head. To much and you get poor cylinder fill and a good chance of hotspots/detonation, too little and you get the same problem.

Rule of thumb, is 0.035" to 0.048" quench.
The trick is the close collision distance, it sends a shock wave/turbulant wave through the combustion area at TDC which helps to fill the chamber, also the shock wave helps cool the combustion surface, as its essentially high pressure air (like blowning on a candle).

[BigWillieStyles]

They don't have the true forged pistons of the aftermarket quality. They have what are called hypereutectic pistons. Its basically a hybrid between full forged and cast. Have a read on wikipedia about them.

Ive read that the recent Sti models (06+) now have hypereutectic pistons.

[Dylan]

Ive read that the recent Sti models (06+) now have hypereutectic pistons.

From where?

Are you able to provide some reputable sources to this?

We need to cut down this 'I have heard' 'I have read' non sense.

I have heard that STi pistons are actually painted pink.

Doesn't make it true.

Back up your claims with REAL evidence or do not post. We do not need to help in the spread of falsities.

[skillionaire]

Hi,

Thats incorrect. Hypeutectic pistons are still cast pistons. Its the metal content that determins whether or not they're eutectic or hypereutectic.

Pretty much, they are cast in the same fashion but have a higher silicone content.

Cheers,
Nik

[Soop]

Its more then just silicon content.
The ANSI stipulates what they need to have in order to be considered Eutectic or hypereutectic.

its varying concentrates of: Nickle, Chromium, Manganses, Molybendum and Silicon. I have the percentages here, but it may be a little bit far for this forum at the moment.