Ej205 block weakness? 207 stronger?
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This is a discussion on Ej205 block weakness? 207 stronger? within the Engine Modifications forums, part of the Tech & Modifying & General Repairs category; Hoping you guys could answer a few questions for me. I know the ej207 big port heads, cams, valvetrain, turbo ...

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    Ej205 block weakness? 207 stronger?

    Hoping you guys could answer a few questions for me.

    I know the ej207 big port heads, cams, valvetrain, turbo and probably intake manifold etc etc help the jdm ej207 make more power than the us ej205, but I am really only concerned with the bottom end, and more much more concerned with strength than I am power.

    I know the jdm ej207 block is semi closed deck while the us ej205 is not, possibly allowing the cylinder itself to move, but what else about the block/bottom end itself makes the ej207 handle more power/tq/more rpms than the us ej205? Completely different crank? stronger rod material/design? Stronger piston material design?


    I feel like the stock 145,xxx mile ej205 in my "stage 2" 2005 Wrx is loosing it's pep and could really use a rebuild or replacement and trying to figure out the best way to go about it.
    I could probably see myself doing a complete ej207 block/head swap if it is possible to do so on my usdm 05 Wrx ecu or possibly usdm 06/07 Wrx. I might possibly think about an ej25 swap but all the ringland/piston failure stories scare me a little (a lot), plus I like the smoother, faster/higher revving 2.0 more than the 2.5. But forget all the 2.5 talk, I am only interested in the 2.0 blocks and what specifically makes the ej207 stronger than the us ej205?

    If different crank, what exactly is different?
    If different rods, is it different material or design that makes it stronger?
    Different pistons?

    I would like to stay 2.0 and oem as possible. Thanks guys.
    Last edited by 4eat05; 05-25-2015 at 06:59 PM.

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    Whats usually the first thing to break on a 2005 us ej205 besides the typical spun bearing? Rods? Pistons?

    I've read the v7 ej207 pistons are forged, and all other ej207 pistons are cast. Are v8 ej207 pistons stronger than ej205 rods?

    Are v7 or v8 ej207 rods stronger than us ej205?

    Are v7/v8 ej207 cranks different than 2005 us ej205 crank?

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    The EJ207 is completely different from the USDM EJ205 in virtually every way. Yes, the block is "semi-closed" but I don't see this as a weak point until big power is in the cards (>500whp). At that point, the EJ207 block isn't much better anyway.

    The big port heads will outflow any other Subaru heads stock for stock, but worked EJ205 heads purportedly outflow even spec C heads, if you're willing to invest the money. The only similarity between the two blocks is the crank in the 2004-2005 WRX that is essentially the same as the EJ207 crank.

    Weak point of the EJ205 is generally bearing fatigue and the weak stock rods. USDM STi and 2006+ WRX rods are an upgrade in this sector. Both the rods and crank are forged in the USDM EJ205, but the aforementioned rods are stronger. All USDM Subarus feature cast pistons. EJ257 and EJ255 are hypereutectic cast as are V8 and later EJ207 pistons. Only V7 STi pistons are forged.

    If you don't like the 2.5L, the best motor build to consider for you is the 2.1L stroker which consists of your case halves reworked, a 2.5L crankshaft, aftermarket or STi rods, forged 4032 alloy pistons, mildly worked EJ205 heads (S1 cams), and head studs. It's a 400whp+ motor that just loves to scream.
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    So the ej207 crank is basically the same as my '05 ej205?

    Are the v8 ej207 hyper cast pistons stronger than my cast ej205 pistons? I've always read the ej255/257 hyper cast pistons are weaker than the ej205 pistons, but never read anything about the v8 ej207 pistons.

    Do the v7 ej207 forged pistons have the same p2w and piston slap "problems" as aftermarket forged pistons?

    Ej207, ej255 and ej257 rods are all stronger than ej205 rods and they all are the same length/work in an ej205? Any of them stronger than others?

    Do you know if v8 ej207 (or even v7) pistons in an ej205 with stock heads would change the compression?

    I either want to do a mild build/refresh of my ej205 using better stronger oem parts, or maybe get an ej207 shortblock if everything works right with ej205 heads and doesnt change the compression too much.

    Sorry guys, really new to Subaru engines. Looking to replace the vast amount I know about Honda's with some Subie knowledge.

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    Quote Originally Posted by 4eat05 View Post
    So the ej207 crank is basically the same as my '05 ej205?.
    It IS the same.

    Quote Originally Posted by 4eat05 View Post
    Are the v8 ej207 hyper cast pistons stronger than my cast ej205 pistons?
    Probably.

    Quote Originally Posted by 4eat05 View Post
    I've always read the ej255/257 hyper cast pistons are weaker than the ej205 pistons, but never read anything about the v8 ej207 pistons.
    No, this is not quite right. First, some facts about hypereutectic material. Hypereutectic pistons consist of aluminum alloy that has a greater incidence of silicon than typical cast pistons. This blend matches the piston expansion much more closely to the cylinder allowing tighter PTW clearances particularly at cold start. Hypereutectic pistons are STRONGER than typical cast pistons but also more brittle and susceptible to cracking under severe pressures (high BMEP or knock events). EJ25x pistons are indeed stronger than EJ205 pistons and very similar to V8 EJ207 pistons, but there are a few things to consider here:

    1. The power ceiling on the EJ25x is much higher than the power ceiling on the EJ205. As a result, other components in the EJ205 will fail before the pistons. The pistons being the weak point in the EJ25x means the pistons are perceived as weaker than the EJ205 pistons. In fact, if you push the EJ205 past the typical failure point to the failure point of the EJ25x, the pistons will likely fail.
    2. The larger bore diameter of the EJ25x means the piston is physically larger. More surface area = more potential failure if high BMEP or severe knock events occur.

    Quote Originally Posted by 4eat05 View Post
    Do the v7 ej207 forged pistons have the same p2w and piston slap "problems" as aftermarket forged pistons?
    It is likely that cold-start piston slap "issues" are more likely to occur with the V7.

    Quote Originally Posted by 4eat05 View Post
    Ej207, ej255 and ej257 rods are all stronger than ej205 rods and they all are the same length/work in an ej205? Any of them stronger than others?
    EJ255 and EJ257 rods are the same part. I don't know about EJ207 rods. All rods are the same length. If rebuilding the motor, I would suggest to spend the extra $$ on a set of aftermarket rods because why not?

    Quote Originally Posted by 4eat05 View Post
    Do you know if v8 ej207 (or even v7) pistons in an ej205 with stock heads would change the compression?
    Yes, it is likely since the quench area and combustion chamber is physically different between the EJ205 and EJ207. This is a silly exercise, however, since the main benefit of the EJ207 is the heads. Swapping EJ207 pistons into an EJ205 is worthless - go aftermarket.

    Quote Originally Posted by 4eat05 View Post
    I either want to do a mild build/refresh of my ej205 using better stronger oem parts, or maybe get an ej207 shortblock if everything works right with ej205 heads and doesnt change the compression too much.
    EJ207 shortblock isn't worth your time. There are many who will suggest that the EJ207 is the best bang-for-your-buck upgrade. I am not one of those people and here's why: Most EJ207s are imported with very little information and no way to validate the history. At best, you are getting a motor of unknown mileage and unknown history. If the mileage is significantly high and parts are severely worn, you may end up spending ~$4000 on a motor that becomes an expensive project. Alternatively, having your motor rebuilt by a reputable shop gives you the peace-of-mind as you will know the full history. The 2.1L stroker I mentioned above is my personal favorite motor.
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    Subaru replaced some EJ207 bottoms in the UK due to what was reported as excessive piston slap, at no cost to owners. The owners experienced great results until the piston slap returned. Finally, after all that trouble and worry, the results of piston slap were... nothing and the failures experienced due to piston slap were zero.

    As to hypereutectic pistons: In this case Subaru absolutely did the correct thing. This particular choice was done with performance in mind. However, performance does not equal horsepower or torque output. Performance equals (and from now on, must always equal until we stop using gasoline motors) lower emissions. So, comparing the HP/torque mods tolerated by hypereutectic pistons vs. others sidesteps the actual intention of the design.

    Given all that and your goals I think you could adapt an EJ207 to your needs but I doubt you should. You'd be dealing with sourcing, re-fitting (gasket set, fueling, etc.) a teenaged motor imported from another country. Instead either pay a reputable firm to build (and I'd go further: install!) a motor to your specs here and take every advantage of their support and any customer service they offer after you drive off, or DIY something. I'd chose the following options:

    1. NOTHING. All you've got is a "feeling" by your own admission. Losing "pep" could be any number of things and at only 145K I bet if it does exist, it's not the motor. Find out if your motor has an actual problem first. If not you're wasting time and money to address a problem that may or may not exist but isn't going to be solved by replacing the expensive parts you're replacing.

    2. Go 2,1+ L or 2,5L depending on who you have nearby and what their usual MO is. I know you dislike the 2,5L solution but larger displacement will help with torque and many are happy with the results.

    I don't mean to offend; just IMO.

    PS. If your motor is healthy (I bet it could be!) then you could try going beyond the stage 2 setup using your existing, healthy motor instead. A different turbo, injectors, fuel pump, inlet and IC hoses could really open up the car, and this is all stuff you'd need if you were to swap the motor anyway -- meaning, if you do end up blowing up this motor you are actually ahead of the game for a swap provided you can take those parts with you to the new motor. Another thought.
    Last edited by SD_GR; 05-30-2015 at 11:05 AM.
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    I would really like to avoid forged pistons due to all the "problems" with them, which is why I was considering an ej207 block, but am very unsure of compression change or how the ej207 pistons would do with ej205 heads/combustion chambers.

    I really dont think I want a 2.5l. I have 2 friends with 2.5l 06 Wrx's. One is just intake, catback, stg1 map, the other is intake, dp, catback stage 2 map, yet I still like my 05 stage 2 2.0l more. Feels much smoother and quicker to rev.

    I just want a stronger 2.0 bottom end that lasts more than 60k miles without p2w clearance/piston slap issues, but dont know how ej207 (v7,v8?) block with ej205 heads, or ej207 piston/rods in an ej205 would work out.

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    I know of no realistic way to eliminate piston slap. I also don't understand why it's a problem. I'm in good company; neither do Subaru.

    In any case, consider the 2,1L suggestion then I suppose.
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    Quote Originally Posted by 4eat05 View Post
    I would really like to avoid forged pistons due to all the "problems" with them, which is why I was considering an ej207 block, but am very unsure of compression change or how the ej207 pistons would do with ej205 heads/combustion chambers.

    I really dont think I want a 2.5l. I have 2 friends with 2.5l 06 Wrx's. One is just intake, catback, stg1 map, the other is intake, dp, catback stage 2 map, yet I still like my 05 stage 2 2.0l more. Feels much smoother and quicker to rev.

    I just want a stronger 2.0 bottom end that lasts more than 60k miles without p2w clearance/piston slap issues, but dont know how ej207 (v7,v8?) block with ej205 heads, or ej207 piston/rods in an ej205 would work out.
    I'll provide some insight as I have recently owned cars with both motors. The EJ205 certainly feels happier to rev. The EJ257 indeed revs as high as the EJ205, but the NVH difference is noticeable. Whether this is from the geometry of the motor or the mounts I cannot comment -- In theory the rocking couple should have higher magnitude with the heavier rotating assembly. That being said, plenty of worked EJ25x motors have been built to rev between 8500 and 9000 RPM. The EJ257 certainly has the geometry to rev if supporting mods are present.

    Your concerns on Forged pistons are not unfounded, however it is likely that you have been researching primarily 2618 alloy pistons. These pistons have a low silicon content and will make short work of the block over 80-100k miles. 4032 pistons are much stronger than stock and will not damage the block as heavily as 2618 pistons. There are documented cases of 4032 alloy builds eclipsing the 200k mile barrier, though YMMV.
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    How much more power/tq can a stock v8 ej207 block/crank/rods/pistons handle than a stock '05 ej205 block/rods/pistons??

    I guess im still way more interested in an ej207 block/crank/rods/pistons under my stock ej205 heads, or ej207 rods/pistons in my ej205 block, but CAN NOT find any useful info on this.

    Would v8 ej207 pistons (maybe v7) in an ej205 raise or lower the compression compared to a stock ej205? Increase/decrease combustion chamber volume?

    I really dont think im too interested in going with a 2.5 block, 2.2, 2.1 or any kind of stroker.

    I'd really like to avoid splitting the case and using forged pistons if I can. Ive always heard the block never lasts as long after being split open, and always read forged motors don't last as long as oem, so I just want a stronger Oem block if possible.

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    dbl post

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    I've given you as much help as I'm willing/can. Best of luck.
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