LanceDa Posted October 4, 2010 Share Posted October 4, 2010 Hello all, I have a engine swap question. I have a 99 outback AT with a 2.5 DOHC and I need to replace the engine block due to a broken head bolt that won't come out. Will a 99 SOHC block fit my DOHC heads, and everything else that I have from my DOHC engine? Also, just a general question for future reference, Are all EJ25 block (EJ25D, EJ251, etc.) blocks interchangeable? thanks for your time and knowledge -Lance Quote Link to comment Share on other sites More sharing options...
idosubaru Posted October 4, 2010 Share Posted October 4, 2010 all DOHC blocks are interchangeable. all SOHC blocks are interchangeable. i don't believe you can swap DOHC and SOHC blocks though, but wait for clarification. Quote Link to comment Share on other sites More sharing options...
LanceDa Posted October 4, 2010 Author Share Posted October 4, 2010 ok thanks. anyone else want to chime in on this? Please -Lance Quote Link to comment Share on other sites More sharing options...
GeneralDisorder Posted October 4, 2010 Share Posted October 4, 2010 Well - we put SOHC heads on DOHC blocks all the time so I really see no reason that this wouldn't work. EJ25 blocks are very hard to tell apart without their heads in place. All the EJ blocks are about the same really just different diameter bores for the different displacements. I beleive the combustion chambers on the DOHC heads are larger than the later SOHC heads due to the later SOHC block's having a shorter pistons that don't pop-up. So you might end up with low-rise pistons and large combustion chambers with that combo..... which means lower compression ratio. I don't see why it wouldn't run though. And you could always just swap the pistons out of your old block into the SOHC block and it should then be basically identical. GD Quote Link to comment Share on other sites More sharing options...
idosubaru Posted October 4, 2010 Share Posted October 4, 2010 i don't believe you can swap DOHC and SOHC blocks though, but wait for clarification. i thought he was talking about EJ25's only and i was speaking to Phase I and Phase II EJ25's. i know you can swap SOHC and DOHC Ej22/EJ25 stuff. But GD do you mean to say you think you can also swap Phase I (DOHC) and II (SOHC) EJ25 blocks? Quote Link to comment Share on other sites More sharing options...
wtdash Posted October 4, 2010 Share Posted October 4, 2010 (edited) According to this site - right here on the USMB - the phase 2 EJ25 BLOCK started in '99 for all Subarus. The Legacy line - OB/GT - retained the DOHC heads; the rest went SOHC. (No, I don't know why. ) Edit#1: Our friends on SubaruForester.org confirm this HERE. Edit#2: I believe the Phase 2 had the 8 bolts between trans/engine as well. So, that leads me to believe that the '99 DOHC heads should swap over to an original '99+ SOHC engine....and that of course means the engine harness - on the DOHC intake manifold- can be reused to ensure all the sensors and wiring stay the same, which I'm guessing is why you want to swap heads? Edit#3: And since I'm one of many that have done it, you can still swap in a '95 EJ22 (block and heads) from an AT into the '99 Legacy OB/GT and it'll run like stock (just slower). Td Edited October 5, 2010 by wtdash Quote Link to comment Share on other sites More sharing options...
LanceDa Posted October 4, 2010 Author Share Posted October 4, 2010 Thanks a lot everyone you guys are AWESOME!! I love this message board, everyone on here is so helpful and there is not a lot of drama and ************************s here. thanks again -Lance Quote Link to comment Share on other sites More sharing options...
idosubaru Posted October 4, 2010 Share Posted October 4, 2010 sweet thanks todd, i hadn't seen much discussion on swapping blocks. that's good to know. Quote Link to comment Share on other sites More sharing options...
Gloyale Posted October 5, 2010 Share Posted October 5, 2010 I beleive the combustion chambers on the DOHC heads are larger than the later SOHC heads due to the later SOHC block's having a shorter pistons that don't pop-up. So you might end up with low-rise pistons and large combustion chambers with that combo..... which means lower compression ratio. Bingo.......unless you swap pistons, you'll lose compression. Swapping pistons does not require splitting the case, but you will DEFINATELY need the oil pan off and the engine on a stand. Quote Link to comment Share on other sites More sharing options...
subaru360 Posted October 5, 2010 Share Posted October 5, 2010 I don't see why it wouldn't run though. And you could always just swap the pistons out of your old block into the SOHC block and it should then be basically identical. GD The rod length is different. It won't work. I can't see any reason you couldn't use a 99 2.5 sohc block with dohc heads except the compression ratio difference. You'd have to calculate it out and see how bad it is. If it's less than a point it should run ok. Quote Link to comment Share on other sites More sharing options...
Gloyale Posted October 5, 2010 Share Posted October 5, 2010 The rod length is different. It won't work. Uh...... I've put SOHC 2.5 pistons into a DOHC block,crank,rods.......works fine. I've also compared SOHC and DOHC 2.5 rods side by side, they are the same. The one difference in the setup is the piston height, and also the length of the wrist pins. SOHC pistons are "shorter". And they have a wider (width clip to clip, not diameter of pin) wrist pin hole which uses the longer wristpins. Quote Link to comment Share on other sites More sharing options...
GeneralDisorder Posted October 5, 2010 Share Posted October 5, 2010 The rod length is different. It won't work. Really? I thought almost all Subaru rods were identical? I'm no expert though..... GD Quote Link to comment Share on other sites More sharing options...
subaru360 Posted October 5, 2010 Share Posted October 5, 2010 Uh...... I've put SOHC 2.5 pistons into a DOHC block,crank,rods.......works fine. I've also compared SOHC and DOHC 2.5 rods side by side, they are the same. The one difference in the setup is the piston height, and also the length of the wrist pins. SOHC pistons are "shorter". And they have a wider (width clip to clip, not diameter of pin) wrist pin hole which uses the longer wristpins. Really? I thought almost all Subaru rods were identical? I'm no expert though..... GD The phase 1 EJ25 has longer rods. So you couldn't put 99 dohc pistons in the 99 sohc block. The pistons would hang out the top of the block. 99 Legacy EJ25 was an oddball. It had 8 bolts engine to trans but was still a phase 1 with #3 thrust bearing, the longer rods and smaller rod bearings. Quote Link to comment Share on other sites More sharing options...
LanceDa Posted January 5, 2011 Author Share Posted January 5, 2011 The SOHC block works with DOHC heads. IT is running like a dream. Thanks for the information. -Lance Quote Link to comment Share on other sites More sharing options...
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