2004 WRX - strange engine rattling when revving up - Page 2
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This is a discussion on 2004 WRX - strange engine rattling when revving up within the General Maintenance, Troubleshooting & Accidents. forums, part of the Tech & Modifying & General Repairs category; Originally Posted by zax yai. I feel like you could pick up new heads for that price. But you'll have ...

  1. #16
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    Quote Originally Posted by zax View Post
    yai. I feel like you could pick up new heads for that price. But you'll have to add head spacers. The reason that the heads require re-machining when going hybrid is because the compression ratio with EJ25 block + EJ20 heads is right around 9.0:1 -- too high. Even then you're not optimizing the quench area for the increased displacement. I would just have them re-machined.
    I can get brand new bare EJ257 heads for $1130 (and get a EJ257 block which is about the same as the EJ255), but I don't think that this is a road I want to go down, since I don't think the EJ205 head internals drops into the EJ257 heads. But, if what you say is true, then you're suggesting that using a different head gasket to change the spacing is still not an ideal solution? Because my plan was to do that - which will drop the compression to at least 8.6. There's a great thread on the EJ255 v EJ257 and the compression ratios with WRX heads here: http://forums.nasioc.com/forums/show....php?t=1667168

    That seemed to indicate that with the right head gasket my compression will be fine. What do you mean when you say "optimizing the quench area for the displacement"?


    (Heads, BTW: http://flatironstuning.com/c-1039-co...and-heads.aspx)

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  3. #17
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    Quote Originally Posted by njoubert View Post
    I can get brand new bare EJ257 heads for $1130 (and get a EJ257 block which is about the same as the EJ255), but I don't think that this is a road I want to go down, since I don't think the EJ205 head internals drops into the EJ257 heads. But, if what you say is true, then you're suggesting that using a different head gasket to change the spacing is still not an ideal solution? Because my plan was to do that - which will drop the compression to at least 8.6. There's a great thread on the EJ255 v EJ257 and the compression ratios with WRX heads here: http://forums.nasioc.com/forums/show....php?t=1667168

    That seemed to indicate that with the right head gasket my compression will be fine. What do you mean when you say "optimizing the quench area for the displacement"?


    (Heads, BTW: http://flatironstuning.com/c-1039-co...and-heads.aspx)
    I honestly would take the EJ205 heads over the EJ257 heads. Assuming that you are not going to swap out for an STi ECU, there's no point in adding that weight from the AVCS hydraulic actuators if unused. Many tests here have shown that EJ205 heads flow better than EJ257 heads anyway.

    About the quench area, if you change out the pistons for aftermarket pistons, you're changing the quench anyway. I'm not saying that a thicker head gasket won't work -- it absolutely will. However, the geometry of the EJ257 heads is slightly different from the geometry of the EJ205 heads from what I've heard, so you might want pistons with similar quench geometry as the EJ205 pistons, except the bore for the EJ20 is 92 mm vs. the 99.5 mm bore in the EJ25. You can run better timing without detonation with an optimized quench volume. As I understand it, the best solution is to machine the EJ205 heads to match a similar geometry to the EJ255. But this is just what I've pieced together. You should probably PM someone like RayfieldsWRX, STI KLR, or brfatal, they are all running hybrid builds.
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    Just to give everyone an update - after weighing all the options, I'm going with a stock EJ205 block to just replace my blown one. I'm picking it up for $1700 from Capitol Subaru here in the bay.

  5. #19
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    Quote Originally Posted by SonicWagon View Post
    Ouch, lots of spun rod bearings in here. That noise cost me allot of money... I could have had a 6 speed....
    Would you be willing to share some numbers? My girls car has a spun bearing.
    thanks

  6. #20
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    Quote Originally Posted by njoubert View Post
    Just to give everyone an update - after weighing all the options, I'm going with a stock EJ205 block to just replace my blown one. I'm picking it up for $1700 from Capitol Subaru here in the bay.
    Was the cylinder walls scorned? why do you need to replace the block? I would think the cranck bearings and maybe a rod, but not the block? I am surely missing something...

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