why not forged internals and a iron block? i just wana know why subaru did this to the usdm sti? Every STi in the world has an EJ20 2.0L engine with forged rods & pistons & a cast-iron block. The USDM STi has cast internals and an aluminum block with steel sleeves

Cast iron blocks eh!

Pop corns made :lol:

Heh... EJ motors are all Aluminum. Other world market STI's got Forged pistons. The US STI and the V8 STI in Japan got Cast pistons. It was not just a change for US only. US STI's have forged rods. Subaru claims the Cast pistons are stronger then the forged. Drawback is they are more brittle. I think they did this for emissions as Cast pistons expand less and run a tight clearance.

There are three basic block configurations. Closed deck, Semi closed deck and Open deck. The US STI is Semi closed deck. The US WRX is open deck. The switch to open deck or semi closed deck was also for emissions and effeciency. With water surounding and cooling the bores the detonation threashold is raised allowing leaner AFR's and more timing. Not to mention more engine life. Drawback is that these designs are not as strong. This does not show up as a drawback until massive cyl pressures and very high hp. These motors are actualy pretty strong. The JDM 2.0 is very strong and can take some serious pressure. The US motor is very strong but it has weak cast pistons. These motors are starting to have a reputation of being stronger and stronger as people learn to tune them correctly rather then trying to tune them as an inline four which they are not.


Clark

You'd have to...........more on this later.

Every STi in the world has an EJ20 2.0L engine with forged rods & pistons & a cast-iron block.


I have no idea where you got this information, but they were lying. Subaru doesn't even sell a car with a cast iron block, anywhere in the world, As Clark of Kingpin mentioned, the new STIs overseas all have the Hypereutectic pistons, just like the USDM.

As far as the cast iron block goes, Subaru has not made a cast iron block at least since the first EA series engine came out (the EA51). You would have to go back at least to the 60s to find one, and I am not sure they made one even then. Again, whoever told you that was smoking something.

You should sell your car in protest.

some guys on evom are telling me this, im new to subaru im still learning everyday on my car so bare with my guys lol and thank you for the info btw :cool:

Its EA52, not EA51 Kent...I cant believe you forgot that on your return trip upstairs. :lol:

You will have to go WAYYYYYYYYYY back to find a cast iron block from SUBARU.

However, there are two basic block casting methods...medium pressure and high pressure. The High Presure is for the more common open deck and semi open/closed deck blocks...aka the EJ205, 207/22E/25D/251/253/255/257/18/15/16...etc etc....

the Medium cast is for the EJ22G/T EJ20G...and thats about it...except for the older EA82/81/71/63 blocks in the older scoobies (as I have one, an 87 RX with the factory EA82 Turbo engine in it, tough as nails) Those blocks are fully closed deck are are still VERY VERY good blocks to have....the drawback to the med. pres. blocks is that the AL holds in heat more, and its much harder to cool down like the high pres. blocks....however, the HP blocks dont have as much strength as the MP blocks....but since the EJ207 and 257 came out...the internals are better and the cylinder wall pinning is much better...so these newer HP '7' series blocks can attain a higher output level, and seem to have much better cooling characteristics than the MP blocks of the 90's.

It is worth mentioning theat the USDM 2.0 pistons are aluminum castings and the JDM 2.0 and USDM 2.5 pistons are Hyper-Eutectic cast. There is a big difference. High silicon content makes them more restant to heat and less likley to expand and catch the cylinder walls. A reported problem with the Forged pistons at high rpm and power.
"cast" pistons are not a bad thing. Hyper-Eutectic castings are used in the EVO I believe as well as many European models.

Hyper-Eutectic castings remind me of magnesium in that the can take extrordinary pressure... just don't drop it or it shatters. Tune the Hyper-Eutectic motors with NO det and they will live forever.

The JDM vpistons are beefier in general than thier USDM 2.5 counter parts. The JDM 2.0 pistons have stronger wrist pins and stronger ringlands. I think the JDM pistons have 5 oil holes still where the US has 4. I would have to check.

So basicly with a USDM 2.0 the block and pistons are plenty strong, but the wrist pins and rods are the weak points? Aslo what about the piston rings hoow do they stack up?

Aluminum block instead of cast iron is there to save weight; that's why an Evo manages to be more nose heavy than a Subaru, at least as far as weight distribution is concerned .... Yes a cast iron block is likely to allow for higher boost pressures in a turbo car ...

There are also thinwall cast iron blocks, eg Fiat/Alfa 4 cylinder but they are still heavier than a comparable aluminum block - this is usually done to reduce weight and production costs.

BMW on their new 6 cylinder generation have gone to a magnesium-aluminum composite block: crankcase and cylinders are in aluminum, whereas the outer part of the block is in magnesium.

Forged internals are preferable to cast for motorsport as ultimately they are going to be stronger. Hyperteutectic (sp?) cast pistons are preferable for a production motor as they allow less piston wall clearance and therefore are better for emissions and quiet running.

Otherwise cast rather than forged internals (eg cranks, rods, etc.) is usually primarily a cost decision.

and the sti has what kind of internals? cast or forged?

The USDM has a semi-closed deck, with forged crank and rods, with hypereutectic pistons. There are now around a half dozen of these blocks rolling around North America with stock internals and over 500 at the wheels, so the block and internals are extremely strong. The pistons are really the weakest point, and they are quite good. With proper tuning they will do quite well.

Actualy IIRC the Justy used a cast iron block. Basicly it looks like that motor was someone else's 3cyl with a Subaru designed 3v stuffed on. I think the 360 might have had one...

Also cast iron blocks are not automaticly tougher. In fact I'd rather have a all aluminum block for full up racing as You can have a forged steel liner section with a massively rigid structure built around it out of aluminum.

More over cast pistons > forged pistons... For the stock car. Would you rather have close tolerance forged pistons that love to sieze in the bore on long top gear pulls or track days, or pistons that are a bit soft and tend to crack when pushed hard? Certainly I'm glad the pistons are weaker than the rods. Its just a shade cheaper to rebuild a nuked STi motor compared to a nuked WRX block because the WRX usualy just tosses a rod through the side of the block. The Sti can actualy be driven around on a nuked motor if you are easy on it. Much easier to take it somewhere to get worked on, as well as cheaper.

what about a hypereutectic forged piston? :) couldn't a forged piston have high silicon content?


and it's hypereutectic or hypereuretic?...it's alphabet soup!! i like to say 'silicon doped metal' or is there more to a hypereutectic alloy than silicon doping?

what about a hypereutectic forged piston? :) couldn't a forged piston have high silicon content?


and it's hypereutectic or hypereuretic?...it's alphabet soup!! i like to say 'silicon doped metal' or is there more to a hypereutectic alloy than silicon doping?

Hypereutectic. Unless it's in a BMW, then it's Hyperteutonic. :lol: I kill me with lame puns. :)

...couldn't a forged piston have high silicon content?...

many do

many do
were the old STi forged pistons silicon doped?

hypereutectic doesnt mean "high silicone content" necessarily, its a certain phase the metal was in when quenched to achieve certain characteristics. I will let someone more qualified make the explaination.:)


Ben

Hyperowhatever, fancy for newer style cast pistons. Still crap on high boost compared to forged. Bad det, broken pistons, add the NAWWWWWWWWZZZZZZZZZZZZZ, have a NOS det event, Shattered pistons.WHat's the debate really? Put forged in if your going to the limits of HP sanity per Liter.

Or... you could tune the car so you do not actually Det.... :rolleyes:
After all det is a loss of efficiency. If you det then the fuel is not being fully used utilized for making power now is it. Det implies in-efficiency no matter the power level man. If you are detting you are not making peak power. You are either not tuned prooperly or have hit the limit of your octane. Those 2 things have NOTHING to do with piston type. :lol:

As far as NOS, use a wet kit and jet appropriately. If you are detting you are doing something wrong and deserve to have something broken.

I see that there are pretty good deals on the Cp forged pistons for the 05 STi. I'm thinking of doing a few mods that include something along the line of the new GT32 kits that people are talking about - with the 51# comp. wheel, dp, up-pipe, ecutek tune, CAI and staying with a TMIC. Would you recommend going with the forged pistons and beefier studs? I've read that they are balanced to within a few grams so they may actually make the rotating assembly better balanced - but not sure if this is the way to go for extending longevity of the motor. :)

OOps - sorry - should start a new thread!!

what about a hypereutectic forged piston? :) couldn't a forged piston have high silicon content?


and it's hypereutectic or hypereuretic?...it's alphabet soup!! i like to say 'silicon doped metal' or is there more to a hypereutectic alloy than silicon doping?


Hyperutetic pistons are cast that have a coating on them. Forged are forged and also can be coated but usually dont need to.

Coatings have nothing to do with it.

Hypereutectic pistons have a higher silicon content in them which reduces piston expansion and makes the piston somewhat stronger. It allows the piston to be made lighter and allows the piston to be designed to create better emissions and fuel economy.

Most engines use Eutectic pistons which also have silicon in them, just not as much. Forged pistons also use silicon. You can make forged pistons that run tighter clearances but the process is more expensive and in a mass produced road going car unnecessary.

Hypereutectic process changes the structure of the metal it's more than just a simple coating.

There's not a single person in this thread qualified to make an objective quantification regarding the long-term properly-tuned det-free strength of hypereutectic pistons.

Well that is true. One can however make certian assumptions based on a known set of data. From that data you can infer new information. So, it is pretty well recognized that detonation breaks pistons. They do not break, generally unless one or more of these accour

A) They are cheap grade to begin with
B) They have some material defect
C) Are being pushed way beyond thier indended use
D) You have alot of detonation

I can not comment on thier long term viability, as well they have not been out long. I can with a high degree of certianty that I will upgrade the motor long before they fail unless I do something stupid.

STi JDM pistons are about as good as they get. Subaru claims increased strength over thier forged pistons. The pressure castings can take is immense. With out detonation I believe it. Just do not detonate.

Am I right? ehh who knows. Seems reasonable though.

this is like why peanut butter with no jelly.... if you have to ask, you wouldnt understand.

other than that cast iron is capola. alu is easier to control temp and believe it or not manufacturers primary concern is meeting emission standards, not making tweekers giddy.

ONe thing that nobody has mentioned in this thread to answer the original poster, the reason that Subaru does not use a cast iron block is also weight. THe Impreza's engine sits head of the front wheels making weight distribution a bit of a chore. If they used a cast iron block the ahndling would be much worse.