taylormac1993 Posted January 9, 2017 Share Posted January 9, 2017 I was just wondering if anyone has built a motor using the 255 shortblock and 25D heads. Seems like it would be pretty easy as all the blocks are virtually the same. I just want to build a stock motor that will run right NA but be able to handle low boost numbers reliably if I decide to go that route in the future. Are there any shortcomings that the 25D heads have when it comes to boost? Also wondering if it will bolt straight up to the stock 5MT trans (clutch, flywheel, slave cylinder differences?) Just tossing ideas around right now and I didnt find anything concrete online. Link to comment Share on other sites More sharing options...
RustyRuu Posted January 9, 2017 Share Posted January 9, 2017 The 255 will have lower compression with the 255 pistons which you could change out for the NA pistons but since you have plans to boost you might be able to leave them alone without too much of a drop in NA performance. The block will need to have a couple extra holes blocked off somehow. I can't remember what they do, possibly oil feed/ return if you plan to keep it NA. the heads might be a lot of work the 25d cams I don't believe are as big as the 255 ones and I know the valve clearances differ so possibly new buckets and shims will be needed but that's gonna be the hardest thing to find info on I think but I'm sure this build has happened before in both your scenarios... Link to comment Share on other sites More sharing options...
taylormac1993 Posted January 10, 2017 Author Share Posted January 10, 2017 I was talking using the stock 25D heads. No cam swap or anything. Sounds like if I want to boost it I should just commit to one engine or the other. I was just trying to get away with not having to merge wire harnesses but with the 25D using a MAF it just wasnt meant for boost without doing extra wiring. A 255 swap would probably be less room for mechannical failure. At least I just want a more stout shortblock to use if Im going to swap one in. 251 might be a better option for NA right? Link to comment Share on other sites More sharing options...
RustyRuu Posted January 10, 2017 Share Posted January 10, 2017 Ipeople have kept the stock ecu/tune. Around 5 to 8 psi but that's all you can get to be still slower than a wrx. A full harness merge and engine that you could continue to tune and mod for more power sounds more fun. The benefits with just the 255 with 25d heads would be as bit more "stout" as you said since it has a Simi closed deck, thicker cylinder walls and you want to match head gaskets to the block and not heads, so you will have the more reliable MLS gasket that comes stock on the turbo models. Link to comment Share on other sites More sharing options...
DOHCEJ22E1 Posted January 10, 2017 Share Posted January 10, 2017 Yes, people have built them. They're still called EJ25D's, and the extra bracing and deeper piston does make these turbo-ready. You would just need to find an EJ20G exhaust cam and install that for better overlap/reaction. Link to comment Share on other sites More sharing options...
twisty Posted January 11, 2017 Share Posted January 11, 2017 Ipeople have kept the stock ecu/tune. Around 5 to 8 psi but that's all you can get to be still slower than a wrx. and still faster than stock legacy, correct? win-win i think. the game isnt always to beat others, but your previous self. Link to comment Share on other sites More sharing options...
doublechaz Posted January 11, 2017 Share Posted January 11, 2017 For me the game has been to get as much power at 5500 ft as I was used to at 900 ft. I also call the game "I win". Link to comment Share on other sites More sharing options...
taylormac1993 Posted January 12, 2017 Author Share Posted January 12, 2017 So you guys are saying I could run the stock ej255 shortblock on stock 25d heads with stock wiring and run 5psi? All in theory of course and I use "stock" in the sense that I dont have to spend days modifying it. Technically it will all bolt up and run a stock size turbo. If this all works my concern would be fueling and using the stock ecu. Link to comment Share on other sites More sharing options...
DOHCEJ22E1 Posted January 12, 2017 Share Posted January 12, 2017 So you guys are saying I could run the stock ej255 shortblock on stock 25d heads with stock wiring and run 5psi? All in theory of course and I use "stock" in the sense that I dont have to spend days modifying it. Technically it will all bolt up and run a stock size turbo. If this all works my concern would be fueling and using the stock ecu. Yes, and you won't have an issue doing so, either. Put the heads on the block, finish it up like you would any other EJ25D, and it'll be a turnkey start. Just make sure you use the 25D crank gear and you're good to go. Link to comment Share on other sites More sharing options...
DOHCEJ22E1 Posted January 12, 2017 Share Posted January 12, 2017 Also to note, MAKE SURE you are using the MLS EJ25D head gaskets, NOT the EJ255 set, if you want a more boost friendly compression ratio: EJ25D V2 heads/EJ255 block - 9.04:1 w/0.6mm head gaskets, and 8.65:1 w/EJ25D head gaskets. If you had a way to control fuel and timing, the latter option would be better for you, but as you want to remain using the stock ECU, do NOT go to that 9:1 line. Link to comment Share on other sites More sharing options...
taylormac1993 Posted January 13, 2017 Author Share Posted January 13, 2017 I just dont know if I want to commit to boosting it yet. Isnt the stock 25D ratio 9.5:1? So I would take a power loss going that route. I could mill the block down but not more than a couple thousandths. That may make up the compression though unless the 255 pistons come up to deck height. This sounds like more work than its worth going NA. I might as well do a complete rebuild on a scrap 25D block and save myself some trouble Link to comment Share on other sites More sharing options...
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