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Old 01-24-2004, 05:25 AM   #1
MJU1983
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Default 2.5 Liter STi tear down (pics, 56k nono)

Nothing special, but some people like to see whats inside of what they have

This block is getting sleeved, and we are replacing the rods/pistons w forged upgrades. Its for a customer in the Netherlands.

-Mike

PS: check out my mad tyte MS paint skills











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Last edited by MJU1983; 05-30-2006 at 11:10 PM.
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Old 01-24-2004, 05:25 AM   #2
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Old 01-24-2004, 05:26 AM   #3
MJU1983
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Old 01-24-2004, 07:17 AM   #4
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Awesome - thanks for the pics!

-st
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Old 01-24-2004, 09:36 AM   #5
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So what is your opinion of the block, rods, pistons ect after the tear down.
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Old 01-24-2004, 11:41 AM   #6
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That might come in handy for me one day. thanks!!
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Old 01-24-2004, 01:02 PM   #7
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Very very nice pics! Now did they make the rod length in the STi slightly shorter to allow for higher revs or is the difference neglible?

and also:
Quote:
roybfr:
So what is your opinion of the block, rods, pistons ect after the tear down.
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Old 01-24-2004, 01:22 PM   #8
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Great Pics!
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Old 01-24-2004, 02:41 PM   #9
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Great pics Mike,,nice job!


Rudy
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Old 01-24-2004, 02:51 PM   #10
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Oddly enough, the 2.5RS pistons look a little beefier then the 2.5STI ones.

The difference in length is normal, as I'm sure Ron knows. There is only about .5-1mm difference in length between all Subaru rods as they mainly move the wrist pin -to- piston crown height around to make them fit correctly.

The ribbing in the case is definitely interesting. I didn't think there was a problem there, but I guess they decided on a little more sturdy case as well.

The tolerance stamps look pretty much right on with everything else I've seen in the 2.5RS blocks. ABAB is really really common... stupid machinists, can't even get them all the same diameter. Only one I've seen that was perfect is the motor that is currently in my car, AAAA.

Would you mind taking a pic of the backside of a stock piston, as well?
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Old 01-24-2004, 03:06 PM   #11
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Quote:
Originally posted by 8Complex
Oddly enough, the 2.5RS pistons look a little beefier then the 2.5STI ones.

The difference in length is normal, as I'm sure Ron knows. There is only about .5-1mm difference in length between all Subaru rods as they mainly move the wrist pin -to- piston crown height around to make them fit correctly.

The ribbing in the case is definitely interesting. I didn't think there was a problem there, but I guess they decided on a little more sturdy case as well.

The tolerance stamps look pretty much right on with everything else I've seen in the 2.5RS blocks. ABAB is really really common... stupid machinists, can't even get them all the same diameter. Only one I've seen that was perfect is the motor that is currently in my car, AAAA.

Would you mind taking a pic of the backside of a stock piston, as well?
I just pointed out the rod length b/c way back when... People were trying to criticize Ronís choice for rod length in the 2.4 stroker motors we make

-Mike
www.axispowerracing.net

He asks and he shall receive:
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Old 01-24-2004, 03:39 PM   #12
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awesome pics!!

thx
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Old 01-24-2004, 04:56 PM   #13
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Hey Great Pics!!!

Last edited by dmpi; 01-24-2004 at 05:02 PM.
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Old 01-24-2004, 05:07 PM   #14
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It's a cast hypereutectic piston. I took it to CP and had them check it out and that's what they told me. They couldn't tell if it was hyper or just plain cast but it's def. not forged.

Block looks nice and sturdy, but the steel liner for the cylinder is exceptionally thin compared to other subaru engines. The 2.2t block has a fairly thick steel liner in it.
Rods actually look less beefier than the 2.5rs rods, but have bolts instead of studs and also have locating pins on both sides of the cap. These help A LOT. Crank looks like bone stock 2.5rs, but with slightly better counterweights and edging. There is no double oiling holes like on all 2.0 sti motors.
All oiling and water passages look similar to other ej series motors.

Ron
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Old 01-24-2004, 05:42 PM   #15
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Thanks for the pic, Mike.

Excellent info, Ron. I was pretty damned sure it was cast due to the texture, but even now, looking at the grid pattern on the side face inside there, you can't do that with a forging.

You still believe it to be hypereuctectic, eh Ron? I guess I could see it, especially if Subaru wanted to get rid of piston slap cases by just making the gap smaller (the HE pistons have a lower expansion rate, right?).
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Old 01-25-2004, 05:44 AM   #16
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Would you mind terribly taking a side view of the piston?

Also, do you know what the rod to stroke ratio is? Thanks!
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Old 01-25-2004, 05:50 AM   #17
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Quote:
Originally posted by Axis Power Racing
It's a cast hypereutectic piston. I took it to CP and had them check it out and that's what they told me. They couldn't tell if it was hyper or just plain cast but it's def. not forged.

Block looks nice and sturdy, but the steel liner for the cylinder is exceptionally thin compared to other subaru engines. The 2.2t block has a fairly thick steel liner in it.
Rods actually look less beefier than the 2.5rs rods, but have bolts instead of studs and also have locating pins on both sides of the cap. These help A LOT. Crank looks like bone stock 2.5rs, but with slightly better counterweights and edging. There is no double oiling holes like on all 2.0 sti motors.
All oiling and water passages look similar to other ej series motors.

Ron
Well I guess that kills the piston debate....


Thanks for the info and the tear down pics.
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Old 01-25-2004, 09:58 AM   #18
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Any pictures comparing the 2.5 STI rods with the regular 2.0 WRX rods? How do they differ in size?
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Old 01-25-2004, 10:42 AM   #19
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Great pics thanks. Just curious, what made you go with the Pauter rods? Was it the customers choice? I have wanted to try the Pauter rods too.

Is there room in the block to stroke the engine? Or do you have the same problem with the wrist pins as on the 2 liter.

What are your plans with the motor besides the bottom end?

Thanks again.

Jeff
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Old 01-25-2004, 11:43 AM   #20
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Quote:
Originally posted by sti'lin
Great pics thanks. Just curious, what made you go with the Pauter rods? Was it the customers choice? I have wanted to try the Pauter rods too.

Is there room in the block to stroke the engine? Or do you have the same problem with the wrist pins as on the 2 liter.

What are your plans with the motor besides the bottom end?

Thanks again.

Jeff
There are places that make 2.6 and larger blocks, but they use the 2.2 block castings...
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Old 01-25-2004, 12:49 PM   #21
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Any proven issues showing that hyper-e pistons are not as strong as forged? I assume that it all has to do with silicon content of the alloy used in the casting and how the "matrix" sets up when the part is cast. I guess time will tell though.

Also, I am in no way questioning CP's analysis of the piston. But, what makes them say definately that it is not a forged part. I just dont know how you can look at it and tell. I would like to know for future reference if anyone or Quirt himself can let me in on that knowledge. The pursuit of knowledge never stops, haha.


RJ
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Old 01-25-2004, 01:41 PM   #22
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Quote:
Originally posted by pio!pio!
Would you mind terribly taking a side view of the piston?
You should probably specify which side... towards the end of the wrist pin, or towards the skirts.

Quote:
Originally posted by sti'lin
Is there room in the block to stroke the engine? Or do you have the same problem with the wrist pins as on the 2 liter.
The problem in stroking these motors is that after you get to the EJ25 crank stroke length, you start to get very close to the edges of the casing with the rod bolts. Most/all of the built EJ25's need clearancing for the rod bolts in the block itself. I imagine if you go too much larger, you'll end up having to clearance enough to almost protrude into an oil galley.
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Old 01-25-2004, 03:55 PM   #23
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Thanks for the pics, very helpful.

So then the consensus is that the USDM 2.5 STi block does not have forged rods? I figured this all along, but this is more of a confimation. Do you think there is anything they have that makes them stronger than the RS or WRX rods?

I am also interested to know how well the hyper-e pistons will stack up to a forged Subaru piston.

Thanks for any info,


Graham
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Old 01-25-2004, 04:15 PM   #24
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Quote:
Its for a customer in the Netherlands.
I am curious who that is?

P.S. I am Dutch and I know (almost) all Subaru enthousiasts overhere....

Mark.
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Old 01-25-2004, 04:44 PM   #25
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woh woh woh, I thought that the consensus WAS that the STi rods WERE forged... I thought that the pistons were too, but that seems to be wrong. Well, if the rods are also cast, then it seems that the STi shortblock might not be much of an upgrade at all for us WRX guys... Whats the deal guys???

RJ
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