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This is a discussion on engine within the Engine Modifications forums, part of the Tech & Modifying & General Repairs category; As some of you here know, my car is having major issues. I will be pulling it into the shop ...

  1. #1
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    Question engine

    As some of you here know, my car is having major issues.

    I will be pulling it into the shop and from there proceed to rip the engine apart to find out what's wrong with it. My instructors and I are thinking possibly a valve stuck or something with the head. However, we won't know until we pull it apart.

    If the issue is with the heads, it's going to be an easy fix. If it is not however, and the block is in rough shape, I was thinking about changing the block to an STi block and using the WRX heads on it. Already going into this project, I know I will need gaskets, a tune, time, and a few limbs to sell (joke).

    I was wondering if there is anything anyone suggests, before ripping the engine apart, if there is something that you would recommend doing while the engine is apart.

    My goal is to get my car to 325 hp.

    I will be upgrading the sway bars while I'm at it, as well as body bracing, making the car more solid. I will also be upgrading my suspension setup, and possibly re-enabling ABS.

    Will the EJ25 short block bolt up to the 5 speed transmission in the 02 WRX? Also, I've been reading that the WRX heads should bolt up to the EJ25 block, is this correct? Is there anything I should watch out for when doing this?

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    If you are thinking about swapping motors, it seems silly if not redundant to put an STi motor in there. If anything you should consider a prebuilt performance motor. Getting 325whp out of the stock block is really asking for trouble due to the motors natural ability to eat up piston rings like they are cheerios. The benefits of an already built motor would far surpass the STi motor. You could essentially run 325-450hp depending on the build quality, which would be conservative and thus result in a motor that can hold power all day long without causing concern for longevity.

    Some shops even offer their motors with a 1 year warranty and they are rated to ~600whp.

    And as far as tranny swaps are concerned swapping a WRX tranny for an older WRX tranny doesnt sound ideal. If you want to do that, then the STi tranny is the way to go. Recommend swapping the clutch for something that will last longer at those power levels, but it's up to you. At 325whp I'd say the stock STi clutch could last you +-60k mi before it starts slipping.

    Best of luck. Not too sure about the other stuff you asked about but I hope my creativity helped a bit lol!

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    Thanks for replying

    I am not planning on changing my transmission. I plan on using my existing one. I was more curious if it is going to have issues bolting to the block.

    I guess the problem is that I was missing some information. I have a 02 WRX turbo with 266 000 kms and I am going to be opening it up to assess the damage on it. So the entire idea was that if I take it all apart replace the block and then bolt everything back up, would there be anything else I should worry about other then the tune and gaskets?

    I will be doing the work myself. Also, I am not very fond of spending money for others to do work that I can already do myself in automotive.

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    I would check the specs or ask a dealer if they would be compatible unless someone on here knows. I dont see any reason why it couldnt work but I may be wrong.

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    Btw theres a video on youtube of a subaru master tech reassembling a motor outside on his driveway lol its very informative and might help you if you have any issues or questions.

  7. #6
    Registered User UEDan's Avatar
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    Heads do bolt up, but you'll have to get the heads machined to match the 2.5l combustion chamber.

    If the block is still in decent shape, why not stroke it?

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    Quote Originally Posted by UEDan View Post
    Heads do bolt up, but you'll have to get the heads machined to match the 2.5l combustion chamber.
    This. You could use the HG spacers, but I just feel like if you're going to do it, do it right. I'd opt for the volume matching on the EJ205 heads. Furthermore, port your heads while you've got them out.

    Quote Originally Posted by UEDan View Post
    If the block is still in decent shape, why not stroke it?
    All the way. The 2.1L stroker motor is a killer piece of hardware under the hood. If you want more details, PM me.
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    I full agree that a 2.1 stroker would be an awesome way to go.

    And to Le Stig up there, there's no reason why a stock STI block couldn't handle 325hp. That's no more than just a Stage 2 tune on a VF39/VF43/VF48. You don't need to go all out engine build for that.

    STI clutch won't fit on a 5spd WRX transmission. Something like a Stage 1 clutch wouldn't be a bad idea, but depending on how you drive, an Exedy OEM style clutch could be just fine.
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    The heads will bolt up, so will the transmission. Do not attempt to reuse the head bolts though, I would at least get some ARP head studs. If you go with a 2.5L hybrid or a 2.1L stroker, you should still go ahead and pay to have the heads torn down and rebuilt. While you're at it, the stock WRX cams will leave a lot of power on the table above 5500rpm, so I would suggest sticking either STi cams ($~120 used) or some S1 cams in there. I wouldn't bother porting if your goal is 325hp.. porting the heads will kill your bottom end, so it's not the best thing to do on a daily driver unless you're running a largish turbo and shooting for 400hp+. You could benefit from a quick bowl blend though.. and it's not necessary to match the combustion chambers for a hybrid build, but that is the best way to go about keeping your compression ratio down (if that's what you want to do).

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    Quote Originally Posted by Mikie13 View Post

    And to Le Stig up there, there's no reason why a stock STI block couldn't handle 325hp. That's no more than just a Stage 2 tune on a VF39/VF43/VF48. You don't need to go all out engine build for that.
    Dude stage 2 STi's make ~290whp on a mustang dyno. 325 real wheel hp is a lot to put on the stock block. Stage 2 cars now a days last on average 2 years before the white smoke strikes (in some cases not even a year.) If you're not running the proper boost control i.e EBCS + EWG you are just setting yourself up for failure especially if you are running those hit or miss OTS maps. Seen way too many subies fall into that. The unfortunate truth with todays EJ257 is that with modding there are really two routes to take.

    1: Conservative stage 2 with plenty of fail safes.

    2: Fully built motor with forged hardware to stand up to those building to reach close to or above 400whp.

    So yeah there is a gray area between the 300-400whp range thats pretty much a crap shoot.

    But the reality is that the even numbered cylinders tend to run hotter than the odd number cylinders (may have it backwards but you get the point) and this over boosting that is all too common when you run ~19-21psi usually leads to ringland failure.

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