Trying to get STI pistons to work....

douglas vincent · Post by **douglas vincent** » Tue Mar 13, 2007 6:49 am

Working on the 2.5 motor.....

Milling phase 2 2.5 rods (longest rods subaru makes I think) to fit STI pistons.

And the results... About 1.92 mm short of the deck. This is using a 2.2 phase 1 crank in a 2.5 phase 1 block with phase 2 2.5 rods with STI pistons.

Splinter · Post by **Splinter** » Tue Mar 13, 2007 6:59 am

What exactly are you trying to achieve?

douglas vincent · Post by **douglas vincent** » Tue Mar 13, 2007 7:06 am

A 2.5 block "brand new" with STI pistons, low compression, 2.5 DOHC heads, all for $350.....

Splinter · Post by **Splinter** » Tue Mar 13, 2007 7:10 am

Not worried about blowing headgaskets with those unbraced cylinder walls?

555BCTurbo · Post by **555BCTurbo** » Tue Mar 13, 2007 7:25 am

Splinter wrote:Not worried about blowing headgaskets with those unbraced cylinder walls?

Why should he be?!?

STi motors are open deck...

BAC5.2 · Post by **BAC5.2** » Tue Mar 13, 2007 12:16 pm

555BCTurbo wrote:
Splinter wrote:Not worried about blowing headgaskets with those unbraced cylinder walls?
Why should he be?!?

STi motors are open deck...

No they arent. Semi-closed.

WRX motors are open deck.

turboleg · Post by **turboleg** » Tue Mar 13, 2007 12:47 pm

Isn't doug's SC setup using a NA block? Not sure that he's worried about having an open deck under harsh conditions.

From what I have read it looks like doug's pretty good at testing the limits of the subaru's arsenal.

Doug,
Your mill and table look like there about as old as mine!

Is this what you were working on the 2.2 to 2.0/2.5 cam gears for?

This going to be the basis for a new SC setup?

gto7419 · Post by **gto7419** » Tue Mar 13, 2007 3:22 pm

Open deck motors can handle a decent amount of power up to a certain point. Especially when paired with the .51 three ply metal headgasket.....

Splinter · Post by **Splinter** » Tue Mar 13, 2007 4:34 pm

2.5NA engines are notorious for blowing headgaskets. We had at least one a week in the shop I worked at.

The center thrust bearing coupled with the unbraced cylinder walls causes the block to flex in the middle, chewing away at the headgaskets.

At least, thats my understanding.

Definately a cool project tho, and if anyone can pull it off, it'd be Douggy, hahhaa.

Post by **DLC** » Tue Mar 13, 2007 7:41 pm

Looks like a Phase II block to me, though I'm not as familiar as some of you.

Looks like an interesting build for sure.

BAC5.2 · Post by **BAC5.2** » Tue Mar 13, 2007 10:18 pm

Also looks like a phaseII block to me. Thrust bearing is at the back of the crank, not the middle.

Matt Monson · Post by **Matt Monson** » Tue Mar 13, 2007 10:46 pm

BAC5.2 wrote:Also looks like a phaseII block to me. Thrust bearing is at the back of the crank, not the middle.

And the crank girdle is reinforced a bit more than the phase I blocks. I personally think that this engine will be a great little toy...

douglas vincent · Post by **douglas vincent** » Tue Mar 13, 2007 11:16 pm

Block in question....

And I don't think its gonna work. The quench area is going to be too big, unless I have the block shaved 1.6 mm......To bring the pistons up flush with the block. What does anyone think?

555BCTurbo · Post by **555BCTurbo** » Wed Mar 14, 2007 12:04 am

douglas vincent wrote: The quench area is going to be too big, unless I have the block shaved 1.6 mm......To bring the pistons up flush with the block. What does anyone think?

That is a lot of decking!

However...since you are Doug...I would say go for it...

mr soul · Post by **mr soul** » Wed Mar 14, 2007 12:33 am

DO IT! Don't bother worrying about quench area as much as some would like you to believe. I know a guy who de-stroked a 2.5 block and left I think like 3 mm of piston to top of bore. Car runs great at 15psi and is a daily driver. He did the whole build with leftover parts around our shop. There is a thread on here somewhere about that. Jibber is his screen name I think.

Good luck, build looks like a cool one and points as usual for unique.
Keith

555BCTurbo · Post by **555BCTurbo** » Wed Mar 14, 2007 1:16 am

mr soul wrote:DO IT! Don't bother worrying about quench area as much as some would like you to believe. I know a guy who de-stroked a 2.5 block and left I think like 3 mm of piston to top of bore. Car runs great at 15psi and is a daily driver. He did the whole build with leftover parts around our shop. There is a thread on here somewhere about that. Jibber is his screen name I think.

Hahahaha...be like 3:1 compression j/k

douglas vincent · Post by **douglas vincent** » Wed Mar 14, 2007 1:50 am

7.3 - 1 with the 1.6 mm gap.

milling the block to a .75 mm gap brings it to 7.85.

Milling it dead flat makes it 8.3.

Using this calculator

http://users.adelphia.net/~wedge138/SUB ... ession.xls

555BCTurbo · Post by **555BCTurbo** » Wed Mar 14, 2007 2:13 am

I would leave it and rock the 7.3:1 honestly...sounds perfectly boost friendly!

mr soul · Post by **mr soul** » Wed Mar 14, 2007 5:07 pm

That's like OLD school compression ratio for boosted application. My GTX was 7.5:1 from Mazda off the assembly line. Talk about a pig off boost with a 1.6 liter.

Again, DO it! But decking it wouldn't add much cost and this looks like a fun build so your call!

IronMonkeyL255 · Post by **IronMonkeyL255** » Wed Mar 14, 2007 5:28 pm

Actually, with the boost you can run with your twincharging system, I think that would be an acceptable CR. You're almost never if ever off boost, and you can cram a whole lot of air into it.

BAC5.2 · Post by **BAC5.2** » Wed Mar 14, 2007 7:19 pm

Matt can confirm, but I THINK old Porsche Turbo's were in the neighborhood of 6.8:1 compression. Now THAT is low compression.

I'd say, give it a shot. What's the worst that'll happen? You'll get bad gas mileage.

But at the trade off of being able to run 40psi...

As far as I know, the rods are exactly the same dimensionally between the EJ22, and the EJ25. I know SVX owners use STi rods as direct dropin replacements for their motors (which, conveniently, are based on the EJ22).

All of your de-stroke comes from the crank. Doesn't the EJ22 have a 77mm stroke, and the EJ25 has a 79mm stroke, or something like that?

Why not run the EJ25 crank, those rods, and those pistons? It won't be a low-comp motor anymore, but it'll be a strong budget build, that lots of people have made lots of power on before you.

Either that, or use that crank in a 2.2L block (either EJ22 or EJ22T) with forged 22T pistons. That'll give you something like 9:1 compression (or close to it), and 2.35L of displacement, which is good for spooling larger turbos. I was going to go this route on my old car.

My vote: Give the EJ25/EJ22/EJ25/STi setup a shot. You might like what it does for you. If you want to bring the compression up, just use the EJ25 crank.

Matt Monson · Post by **Matt Monson** » Wed Mar 14, 2007 7:25 pm

Porsche actually went as low at 6.5:1 on some of the early cars. I would run it as is. If you start decking the block, you are you going to have to mill bigger holes into the intake manifold to make it bolt up and you will need adjustable cam gears to get the timing right. If you mill it, you will advance timing on one bank of cylinders and retard it on the other. Run it like it stands is my vote.

I've talked with 206er about building one of these before. I had all the parts to do it, but with USDM NA pistons, and then I gave my Ej22e core to a racer in need. Maybe someday. I have just gotten used to taking a back seat to Doug's motivation and follow through...

206er · Post by **206er** » Wed Mar 14, 2007 8:25 pm

Matt Monson wrote: I have just gotten used to taking a back seat to Doug's motivation and follow through...

havent we all?

yes the motor we spoke of is probably the best bang for the buck out there.
when did you get a mill doug?
what length are the phase 2 rods?
do they have the same crank journals as phase 1?
why exactly are you machining them, are the sti rods narrower?
which headgaskets, thin ones right?

Matt Monson · Post by **Matt Monson** » Wed Mar 14, 2007 11:47 pm

It has to do with wrist pin sizes...

IronMonkeyL255 · Post by **IronMonkeyL255** » Thu Mar 15, 2007 12:54 am

Matt Monson wrote:It has to do with wrist pin sizes...

That's what I was thinking. That's what it looks like he's milling in the photo, anyway.

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Trying to get STI pistons to work....

Trying to get STI pistons to work....