Mad Mechanic

I'm not sure I follow your statement. I agree that longer rods will give more compression, the longer rods being those for the 251, but your second part about needing a thicker head gasket if I use 251 rods and pistons. I'm starting with a complete 251 block, so wouldn't the block/heads already be setup to accommodate the longer rod/piston combo?

So I hope I'm not past the time limit for resurrecting a thread, but I had a question about connecting rods. My EJ251 has the "odd ball" 131.25mm connecting rods as opposed to the more common WRX/STi 130.50mm connecting rods. Now, I have a suspicion that Subaru put slightly longer con-rods in the EJ251 because it was never intended to be a Turbo motor, so this was a way to increase the compression ratio on an N/A motor. But when I start in on the rebuild of this motor, bearing in mind I don't have intentions of forced induction (talk of supercharging aside for the time being), would there be a good reason to get a set of WRX/STi spec (130.50mm) rods? They are more commonly available. The biggest argument I could see against doing this would be a loss of compression ratio and therefore power. Thoughts?

Pulling a later ECM poses two issues for me given my chosen motor (the EJ 251). First is the lack of a drive-by-wire on the base motor. Now I might be able to get around this by transplanting a later intake manifold from the ECM donor car, but I do prefer an old-school throttle cable (personal preference). Second is that I chose the 251 specifically for the MAP instead of MAF for calculating intake volume, when Subaru went to the 253/254/255/257, they all use a MAF. So again I would probably have to transplant the ECM donor car's instake manifold AND air intake system for the MAF sensor. I've thought about a supercharger at times, there is additional cost (parts and fabrication) involved in going that route, but there are some advantages too. For one, it is a simpler system than a turbo, but the flip side of that is you don't (typically) see the "massive" power gains that turbo setups get. On the other hand, supercharger power tends to come on sooner as you aren't waiting for a turbo to spool. Plus, who hasn't dreamed about a Mad Max style supercharger sticking through the hood. I have also thought that the Subaru intake manifold (or a custom one) would make a perfect platform for a roots blower, similar to a V-block engine. As for camshafts, I've come across several options for those online, everything from aftermarket manufacturers that offer off-the-shelf ground cams for the SOHC engines to a couple custom cam grinders that allow you to specify what you want.

I'd rather not sacrifice my low end as that is where this engine would primarily be used, and I'm surely not building some 2.5L dyno queen. So we have established that the 251 block is plenty fine for what I want to do, however I need to address issues like oiling, so where is oiling a problem on this engine and how do I improve that? (links to other threads welcomed). Also, is there a way to move the torque band lower in the RPM range? According to wikipedia (I know it's not a great source of info but it's a start) peak torque for the 251 is found at 4400 rpm. Would I need to be looking at a set of camshafts? As far as rods, should I stick with the stock cc length of 131.6 mm or look at 130.5mm cc length rods? (I suspect going to the shorter rods would lower my compression ratio and defeat the purpose of what I'm trying to do). For ECU/EMS, I pulled the stock ECU/EMS with the engine, but from my reading I get the impression that was a fairly pointless thing to do (other than maybe trying to bench start the engine in stock form). My understanding is that the stock ECU/EMS from a 2003 outback is not tuneable. Could I pull a stock ECU/EMS from a later car that allows aftermarket tuning or just replace with an aftermarket unit like a Hal-Tech?

More than anything I'm interested in tinkering with the potential of the 251 in SOHC N/A form. I'd like to extract a little more power than the 165 rated HP and 167 lb-ft torque. How much more I don't know, I've read accounts of people spending crazy amounts of money trying to get power near stock WRX turbo motors (some claims more credible than others). Not looking for high RPM power, looking more for power at normal driving revs, the "fun zone". I'm probably going about this the wrong way and if I really want to mess with an N/A motor I should probably look for a 254 DOHC, but this was the motor I chose to start with.

So back to my original post topic, I'm still trying to decide if my EJ251 block is worth messing with from a structural strength standpoint. I'm sure the block itself is perfectly serviceable if someone just wanted to do a rebuild and shove it back into a daily driver, but that's not my ultimate goal with the franken-build I've got rolling around in my head. I contacted a local auto-dismantler that will sell me an EJ255 non-turbo shortblock for $1300, I would then use this shortblock with my SOHC heads and EJ251 MAP intake manifold. Might seem a bit backwards, but as I said I like the design and serviceability factor of SOHC setups. $1300 seems a bit steep to me honestly, considering I pulled my entire complete EJ251 with full engine harness and ECM from a local Pick-n-Pull yard for around $350. So, thoughts on my original post topic?

Hello Subie Rat, Your 200k miles suggestion could be an issue in my case as I have no idea how many miles are on this block. The donor car had a digital mileage indicator, so mileage already accumulated is unknown. I wonder why your mechanic recommends getting a new block at 200k? I'd always heard that subarus are fiercely reliable cars with many examples racking up several hundred thousand miles on them.

Hello fellow forum members! So I'm looking for an honest opinion on this. Last year I pulled a used EJ251 out of a 2003 Outback that was in a self-service (Pick-n-Pull) auto yard. I've been wanting to experience a full engine tear down and rebuild, so I pulled this motor specifically because I wanted the simplicity of the SOHC setup. I also wanted a MAP equipped motor. I have ambitions of using this motor for...something...at some point (famous last words ) but what I'm more thinking about now is this: is the block even worth using? The block itself is in good shape, there is even still evidence of factory crosshatch in the cylinders. But being an EJ251, the cylinder supports are the "least desirable", just thin little bits of metal at the ends (see picture). Now, I don't really have ambitions to turbo charge this motor, but I would like to tinker with it in N/A form (I'm a mechanical engineer by profession, it's often in my nature to tinker in the most challenging route possible). If the consensus is that this block just isn't worth messing with, that's fine, I will turn it into a coffee table or something, but in that case, what block should I be hunting? I really don't want to shell out for an STI shortblock, in fact whatever block I end up with I want to transfer over my good parts, like my SOHC heads. Something else to think about is that this EJ251 block uses the oddball 131.6mm CC connecting rods, whereas later EJH25's used the more common 130.5mm CC connecting rods. Would it be worth trying to find one of those blocks? I would suspect my heads would still fit. I am looking for constructive responses please.

Hey there AdventureSubaru, Thanks for the info, I think I remember reading somewhere that this is the same motor that was used in the 99 through 2003/4 Impreza RS, which would coincide with your information. I'm not sure what I'm going to use the motor for exactly, but I have some custom built car ideas that I'm playing with that utilize off the shelf Subaru drivetrain and suspension components. The biggest design "headache" I have right now has to do with the suspension actually, and this might warrant a dedicated post to the correct sub-forum but it has to do with parts interchange. So from my research using parts.subaru.com I've found that the Impreza from '93 through 2007 had press in front wheel bearings and hubs, but in 2008 they went to a bolt-on style wheel bearing and hub. From a maintenance engineering perspective I really like this, but I also like the front lower control arms on the '93-2007 Impreza as opposed to the 2008. So the question that has been going through my mind is can I put front steering knuckles from a 2008 Impreza onto the lower control arms of a '93-2007 Impreza. I think the answer is yes because as I discovered ALL Subarus from 1987 - 2016 use the same front ball joint (part 20206AJ000). Again, this might be opening up a discussion better suited for a dedicated post on a different sub-forum rather than an introduction thread.

If you can devote a SOLID weekend and have the tools and hopefully at least 1 friend you can wrangle into this, yes, it's possible. I pulled that exact same engine from that exact same year and model car from a junkyard last year and tore it down completely in 1 day. That was arriving at the junkyard in the morning, pulling the engine (took longer than necessary cause I was also pulling the entire engine and body harness too), getting it home, onto an engine stand and bolt-for-bolt stripping it down. So you are going to have to disconnect the fuel lines, electrical connections (thankfully if memory serves its really just 3 big connectors on the intake manifold). Hopefully you have a manual car which will make things a little easier. Get the intake manifold off, timing cover off, pull the cylinder head then comes the crappy part trying to pull the piston head. I would suggest reading up on how to properly remove and install Subaru EJ pistons, this ain't your american V8, the connecting rod DOES NOT come out with the piston head, there are four threaded access plugs on the block, they take a big alan wrench to remove, these are for accessing the wrist pins for each cylinder. take out the access plug for the cylinder in question, rotate the crankshaft to line up the wrist pin with the access hole, remove the snap clip and use what is essentially a flat-head screwdriver with the tip bent down to pull the wrist pin out. This separates the piston head from the connecting rod. After that you will have to figure out how to get the piston head out of the cylinder. Installation is reverse of removal. If you work hard and have the proper tools (engine lift, engine stand) and an extra person, you could probably does this in a solid weekend. Start Friday night as soon as you can, have the engine at least disconnected and ready for removal from the car or better yet remove it from the car. Saturday morning tear the engine apart and get the piston out. If you have the parts on hand, hopefully you can get the piston back in the engine on Saturday as well. Sunday get the engine back in the car and give yourself plenty of time to chase any gremlins (like electrical connections you forget, fuel lines, etc).

Thanks BakedPotatoeChips! I know that the EJ251 isn't a very popular engine to start with but I purposely chose this engine because of the simplicity of the SOHC heads and because the spark plugs and timing set are easier to service. Plus, even though it's not nearly as popular as the DOHC flavors, there are still companies out there making things like performance cams for these engines.

Greetings everyone! So! I don't technically own a Subaru yet (working on it) but I do own a junkyard used EJ251 pulled from a California spec 2003 Subaru Legacy Outback wagon. I have plans for this engine and I have lots of questions to go along with it regarding Subaru drivetrain and suspension. I've heard these cars are like playing with Legos, LOTS of interchangeable factory parts, so that's where I'm hoping this community can help me out. A little about me, I'm a Mechanical Engineer by day and a tinkerer by night. I love daydreaming about custom car creations or modifications I can do to existing designs (hence the 'Mad' Mechanic). Anyway, take care and good wrenching!