fb25 engine swap considerations

context:

2008 (fourth gen) naturally aspirated legacy sat on ramps in my driveway the whole summer with the oil drained and oil pan removed; i primarily suspect corrosion to the rods are suspect since now the car is back together, but you can now see silver metal in the oil, overheating engine, and faint taps in early stages of rod knock.

objective:

now i want to retrofit the FB25 motor from model years 2013-2014 legacy/outback (or 2012-2013 forester; this model year retains hydraulic power steering pulley) but is the current motor, but there are some differences to note. so, i would appreciate if anyone has insight on if this can be done. (i hae already heard the complaints about the newer motors, but as someone shopping for an engine the fb25 engines are a full generation younger, supply and demand has made the FB25 cheaper than the EJ25, and i appreciate the timing chain; next, the oil pan shape accommodates a bolt on garrett turbo from 2015+ wrx for a low boost application, which was the original reason my oil pan was off for fitting, causing the whole issue)

more info:

in model years 2010-2012 the (fifth generation legacy with ej25) moved to ignition coils from plug wires and distributor cap; so this is the first question, is the ecu from fourth gen still plug and play here even with the early fifth generation model years where the motor is still an EJ25 SOHC. In 2013-2014 model years it moved to twin cams and a timing chain and significant hardware internal hardware changes with the FB25 motor, but the harness seems mostly the same with the ej25 motor from earlier fifth gen legacy, but it is unclear if ecu would be blind to these changes.

question:

can i use the ej25 ecu from fourth gen on this new motor, in particular noting the physical coil wiring difference?

i suspect the harness connections will all connect inside the engine bay and into the original ecu; actually the fb25 ecu from 2013-2014 is still physically identical from fourth gen, as you can compare from pictures. if needed i can connect fb25's ecu, but wondering if it would be necessary; next, granted it is going to run, i have the intention to run logs and tune it with the romraider software and a tactrix cable, but the primary question is if the fourth gen ecu can run this engine

will transmission differences (cvt from 13-14 versus 4EAT from 08-09) impact startup and operation

appreciate any input omg thanks

If you were try to attempt to use a FB25, I would think that easiest way would be to used your 2008 ECM and try to adapt the motor to your wiring harness and bolt on your accessories assuming they fit. I do not know if this will even work. The exhaust is probably different and you might need to tune the tune ECM as well. The FB ECM is going to be difficult to work with considering it has a CVT and trying to integrate the can bus. The early FB25 also were parts of oil consumption class action lawsuit which might be another reason why they are cheaper.

I would just get an EJ that fits your car. What ever money you may save will be worth it in the time researching the conversion and less aggravation. I does not seem that logical to do a major swap for one 170 hp motor to basically another 170 hp.

Just a quick note, the 2015 WRX low mount turbo also requires an oil scavenge pump like the 5th Gen GT have. (Different cylinder head with a notched passenger cam to run the pump) The FB25 is not going to have those that to easily plumb that (neither is your EJ253).

My primary concern is putting the stock motor in first , but as for the possible turbo oil return and feed, i was just planning to use an oil filter sandwich plate at the oil filter to pump and return the oil; is this a bad idea or a bad product altogether otherwise?

If you were try to attempt to use a FB25, I would think that easiest way would be to used your 2008 ECM and try to adapt the motor to your wiring harness and bolt on your accessories assuming they fit. I do not know if this will even work. The exhaust is probably different and you might need to tune the tune ECM as well. The FB ECM is going to be difficult to work with considering it has a CVT and trying to integrate the can bus. The early FB25 also were parts of oil consumption class action lawsuit which might be another reason why they are cheaper.

the 2008 ecu is on the canbus already; so you are saying the fb25 ecu would require the cvt tcu in order to work? this is one of the main questions i have here since i only know how to order parts and seeing if they would work afterwards

Just saying/asking, wouldn't it be easier just to do what most of us do ?

Buy a OEM ej257 short block, have your heads rebuilt, install and drive the car.

Just saying/asking, wouldn't it be easier just to do what most of us do ?

 

Buy a OEM ej257 short block, have your heads rebuilt, install and drive the car.

i'm open to this, but this is way more costly; if i go this route i would also replace the crossmember so i can have the option to turbo with the aftermarket exhausts. hoewver, i find the rear turbo location a bit cluttered

as far as the fb25 option, i called a few shops and found i would have to retain the ej253 ecu together with the original harness; then, since it runs wires instead of coils, i would just have to plug in the wires with the plug boots in place of the coils on the FB25--- does anyone know if this would work, or am i a madman for even thinking this

hmm it could work if i just re do the valve covers and slap on ones from the ej

omg thanks

help

Oh sorry, I missed that, 2.5i. Never mind.

We don't recommend doing that swap. way more money and time then what you get for results.

I don't think that ej253 ECU will handle the turbo...

Just put a junkyard engine in that comes with a some type warranty for a few weeks.

I'm getting confused. Do you want to put a NA engine from a 2010-2014 in your 2008 and then turbo it ?

We say, if you want a GT like car, go buy a GT.

i think id rather junk the car completely than put in the same motor from a junkyard; if i were to do so and to sell it right away, the net cash flow is equivalent to calling a junk truck to begin with, so there

the fb25 option is still there, but like i said, i would keep the original harness, ecu, and valve covers. if i win my hastily bid copart auction for a 2013 in a couple days, it is happening.

another option is to transfer the entire drivetrain with cvt into the fourth gen legacy together with the fb ecu, tcu, etc. does anyone know if this would work with my rear differential?

omg thx

My primary concern is putting the stock motor in first , but as for the possible turbo oil return and feed, i was just planning to use an oil filter sandwich plate at the oil filter to pump and return the oil; is this a bad idea or a bad product altogether otherwise?

Most turbo engines use gravity to drain the oil back to the engine, a low mount turbo needs a sump and pump for it to work.

If you want a turbo 4th gen buy Legacy GT/OBXT. If you want a project, blown motor example come up for sale with some regularity, they aren't that expensive and it just isn't worth it.

Sorry I don't ahem the answers to the FB25 swap, but I think your in for a lot hassle for a 2.5i engine swap that doesn't have any aftermarket support for a turbo.

Most turbo engines use gravity to drain the oil back to the engine, a low mount turbo needs a sump and pump for it to work.

 

with a sandwich adapter at the oil filter, im not sure i see a need for sump since oil is not gravity fed in the first place; isn't the oil filter pumped from the oil pump; it pumps out one hole and pump back through the other, or is the pressure at the filter insufficient?

 

2.5i engine swap that doesn't have any aftermarket support for a turbo.

 

that is definitely true for the ej253 2.5i, but the fa/fb engines oil pans accommodate a bolt-on garrett turbo from 2015 wrx with a tactrix cable and romraider on linux or windows

I think you should try. If you can get it to work, post up results.

As others have suggested, you are likely in for a bit of programming. The romraider system uses java, so you could modify the code to add any features you would need

honestly it

so i am basically going to swap the entire drivetrain, and, knowing this is the plan, i am now more interested in 2012-2014 imprezas the with fb20 motors, motivated mostly by similar chassis size; there is a chance i will require the crossmember from the impreza--hopefully not, but this is probably not an option with fifth gen legacy

And on why i have come to this; so, FLlegacy says the sohc program cannot efficiently run the fb25 dohc motor:

As with most cars nowadays the ecu isn't blind to anything at all. The canbus system is very unforgiving in these cars. I don't believe a sohc ecm will run a dohc motor in any subaru without eliminating the extra sensor somehow.

The ecm uses the cam and crank sensors to determine mechanical timing and to set programmable timing. My understanding is the two engines (sohc and dohc) use the sensors differently. Also the FB motor uses dual avcs which cannot be controlled by the sohc ecu. This is why the engine has multiple cam sensors and also oil control solenoids.

 

Now, say you do get the ecm to run the engine using a single cam sensor input, now you have crippled all the advanced hardware on the engine and taken your power output all the way back to like 1996.

 

There is almost no case in which this would make any sense to do, unless you happen to have an FB engine laying around free to you, and you absolutely needed it to work in your sohc car. But even then the fb25 would be worth more to someone looking for one than a sohc ej25 would cost in a salvage yard.

There are a ton of variables. One concern would be that Your car has single avcs and I believe the fb has avcs on both the intake and exhaust so your stock computer won’t be able to take advantage of that. As far as getting your stock computer to run this motor, a lot of stuff like temps and mass air would be easy to figure out but the reluctor on the crank positioning and the cam positioning might be unrecognizable not to mention (and I’m not familiar with the fb) I’m sure the fb having dual avcs may have up to 4 cam positioning sensors. I think you’d be stuck with using the fb harness and computer.

I’d love to see this done and I’m all about the absurdity of it but I bet it’ll nickel and dime the hell out of you. It’d be easier and more economical to buy a cheap and hopefully wrecked lgt of the same gen and swap everything over and part out the rest of the lgt.

so it's become clear that it's only possible to do a complete swap with automatics, in this case a complete fb20 drivetrain; actually from what has become clear already the automatic lgts would be hard to do any kind of swap that wouldn't also be a complete one since the ecu is tuned to a 5eat

one question that remains is if the rear differential on the 2.5i fourth generation legacy is compatible with the fb20 and cvt; and, for that matter more generally what might be a compatibility issue between the rear differentials and 5eat vs 4eat vs manual.

omg thanks

That's the plan, and it looks like i will need the main dash harness since the tcu connectors look different (cf. ebay pictures); whatever i can pull the dash again

My fourth gen legacy has a modified suspension--2004 outback struts with 2015 wrx lowering springs whose only purpose is to accommodate huge wheels while roughly keeping stock height; also have invidia pipes, so it is a lot to throw away if i were to junk it or a lot of work to get it out, so this is the predicament that motivates the project

I say go for it, I would think it would be best to learn how to tune/program.

Maybe look for a FB manual transmission as well.

You will have to retain your 2008 ecu, since the immobilizer needs it.

FB25 has variable AVCS intake and exhaust, which your ecu will not control.

If your car has manual transmission, you could use a standalone ecu.

Otherwise the only way is a complete body harness swap from the donor car including all immobilizer components. If it's an automatic, a transmission swap also.

so, a little belated detail for completeness

the foresters between 2011-2013 are all fb25 engine with 4EAT transmissions lol; moreover, crossmember (engine cradle) compatibility is retained between engine generations on the forester backwards through 2009 and is the same on the imprezas turbo and nonturbo from 2008-2014, according to part numbers. #this is a no-go for the 2010-2012 legacies/outbax where the oil pan would hit the crossmember at the upper and lower pan rears; these aren't fb25s but they are ej25s with an oil pan unique to the fifth gen to accommdoate the garret turbo from the fa20

the reason this is significant is any other model and year with the fb25 automatics will have a cvt and require a complete drivetrain swap complete with dash harness and tcu; also it wasn't clear from the other models and years about crossmember compatiblity. so one could just drop in an fb25 motor, and all you need is an ecu from a forester from these model years to complete the swap while retaining your 4eat; i checked the tcu for these model years, and it appears to look identical, so a dash harness swap would be also unnecessary unlike the cvt models (i.e., imprezas, legacies). so for anyone wanting to make a swap this is the way to go. #also need forester biu, instrument cluster, and key--or follow this guide.

so?

you're not doing this?

im just saying it just got a lot easier after a little more research on model years; anyone with 4EAT can put in a FB25 motor with a forester ecu from the early model years that make it compatible, and this is probably around the same money as a head gasket job on your ej253. plus, the fb25 long blocks retain interchange compatibility through 2018 #but worth pointing out if i already didn't they ship with hydraulic power steering pulley only in the early models years for each model, so you would have to shop for this too

so? you're not doing this?

i will fix my headgasket first, and then do a swap; it is in the agenda but uncertain when

Some good info here, however,

FB25 has an engine mount connecting the engine to the lower radiator support. EJ25 cars dont have a provision for this mount.

Other concern, its highly unlikely that the gauge cluster and the BIU from FB car will be plug and play for the harness in the EJ car.

Next, the VIN number is stored in the ECU. when ECU is swapped and the car is scanned when being smogged, the VIN will not match. You will need to edit the EPROM in that ECU. I've done model year 2005, but unsure is the next gen ECUs use the same code.

FB25 has an engine mount connecting the engine to the lower radiator support. EJ25 cars dont have a provision for this mount.

Do all FB25 have this front mount, ie Forester? The 5th Gen EJ253 and EJ255 have this front engine mount. The 'engine mounts' are located further back on the transmission.

Not sure if all but my 6th Gen Legacy has it. I was not aware that 5th Gen cars do not have that mount.

An FB25 from a Forester had engine mounts that were similar, maybe identical to a 2nd Gen Legacy.