Viability of complete FA24 swap (motor and ECU)?

[Tatsu333]

Now that the ECU has been cracked and tuning is possible, anyone have any input on how viable a complete FA24 (motor, engine harness and ECU) swap would be into a 1st gen?

I have ZERO idea on compatibility between harnesses, etc., and whether the 2nd gen ECU would drive the 1st gen instrument cluster, etc. but thought maybe other folks might have some clues.

...and before anyone throws these options / opinions out there, yes, I know other swaps (E.G. K swap) or forced induction would likely be cheaper ways to get more power. That's not what I'm after.

I'm also well aware of the "RTV is killing FA24 engines" hysteria, and don't want to further that discussion here.

Basically just looking for any input on whether it's possible that it could be relatively plug-and-play if one could source a complete motor, harness and ECU from a wrecked 2nd gen, or if there is likely to be greater complexity to this swap due to something I'm not considering.

Fire away!

[RedReplicant]

I am guessing this is more going to be a case of how do we adapt the second gen to the first gen electronics.

Also, a KSwap is both not going to make more power than a FA24 out of the box or be cheaper, haha. The out of the box kswapped cars are making 200-205whp on pump gas on the NASA classing dynos, the stock second gens are making another 6-10% on top of that.

[Tatsu333]

Originally Posted by RedReplicant

I am guessing this is more going to be a case of how do we adapt the second gen to the first gen electronics.

Yeah, that's kind of what I was thinking. With how many systems are tied together in modern cars, that could be a major rabbit hole to be heading down.

The dream would be that the 2nd gen ECU is plug-compatible with the 1st gen (I.E. the connectors are all the same and the pins all do the same things in the same places with the same voltages), but it's probably unlikely.

It may ultimately be simpler to go the route of doing an FA24 short block swap, keeping the heads, electronics, etc. all FA20. Not simple (because there's a lot of stuff that would have to be done to make it work), just simple-r...LOL!

Originally Posted by RedReplicant

Also, a KSwap is both not going to make more power than a FA24 out of the box or be cheaper, haha. The out of the box kswapped cars are making 200-205whp on pump gas on the NASA classing dynos, the stock second gens are making another 6-10% on top of that.

Very different to hear that from someone who HAS a K-swapped BRZ. Usually it's more like "K-swaps are the best EVER"

I know the K-swap probably has more ultimate potential, but I would really only be interested in FA24+headers+tune kind of power levels anyway. The problem with an FA24 right now is they're hard to come by, so $$$...

[NoHaveMSG]

Cracking the ECU on the second gen isn't going to help the situation.

I messaged Headgames who modifies EJ20 heads to work on the 2.5 block but their only comment back was "never heard of it." So I dunno.

[Tatsu333]

Originally Posted by NoHaveMSG

Cracking the ECU on the second gen isn't going to help the situation.

The relevance is that with the 2nd gen ECU now being tunable, the "advantage" of going the short block swap route instead to have a tunable 1st gen ECU for further mods goes away.

That shifts the difficulty away from mating FA20 and FA24 mechanical parts together to the relative compatibility between 1st gen and 2nd gen ECU's with the 1st gen's other systems.

Which would be a bigger hurdle to overcome? I have no idea - I'm just hoping someone else might have more insight on the latter.

Originally Posted by NoHaveMSG

I messaged Headgames who modifies EJ20 heads to work on the 2.5 block but their only comment back was "never heard of it." So I dunno.

I have heard of EJ block swaps where they left the "step" of the smaller bore heads on the 2.5 block (I.E. they didn't enlarge the combustion chambers to match the bigger bore), but that just seems wrong to me for a number of reasons. I'm sure with a direct-injected, NA motor, the effect it would have on mixture swirl, etc. would be no good.

I guess a first step to assess the viability of the block swap would be to compare head gaskets from an FA24 and an FA20 to see whether or not things even line up, but I currently have other things to spend $200 on...LOL. FWIW, there seems to be a LOT of space between the bore and any other holes (coolant passages, etc.) in the FA20 head gaskets, but I can't even find any pictures of the FA24's head gaskets to compare.

If anyone on here happens to work at a Subaru parts counter and could just overlay the two for funsies that would be helpful...

[DarkPira7e]

Why would you want to swap in another Subaru engine?

[NoHaveMSG]

Originally Posted by Tatsu333

The relevance is that with the 2nd gen ECU now being tunable, the "advantage" of going the short block swap route instead to have a tunable 1st gen ECU for further mods goes away.



That shifts the difficulty away from mating FA20 and FA24 mechanical parts together to the relative compatibility between 1st gen and 2nd gen ECU's with the 1st gen's other systems.



Which would be a bigger hurdle to overcome? I have no idea - I'm just hoping someone else might have more insight on the latter.

You wouldn't want to use the 2nd gen ECU. Might as well just go stand alone at that point. I doubt it would work with the first gen immobilizer anyway.

[Tatsu333]

Originally Posted by DarkPira7e

Why would you want to swap in another Subaru engine?

Just...shut up...LOL. Seriously though, I get where you're coming from. The ultimate power potential with other swap options is potentially much higher, but swapping in something from another manufacturer and running a standalone isn't anything I'm interested in at all.

I just want the 2nd gen's level of power (+headers and tune) with factory reliability and minimal headaches.

Originally Posted by NoHaveMSG

I doubt it would work with the first gen immobilizer anyway.

Ah - see, that is the kind of thing I hadn't thought about.

My experience with swaps is limited to 80's and 90's VW's, Honda's and Mazda's, back when things were much simpler (I'm old...LOL), and there was broad compatibility across different models / product lines.

So it is still likely a simpler solution to try and make the block swap work. I know someone who would probably be up for doing the work, but I don't have the budget yet. Just trying to figure out the best route forward.

[NoHaveMSG]

Originally Posted by Tatsu333

Ah - see, that is the kind of thing I hadn't thought about.

My experience with swaps is limited to 80's and 90's VW's, Honda's and Mazda's, back when things were much simpler (I'm old...LOL), and there was broad compatibility across different models / product lines.

So it is still likely a simpler solution to try and make the block swap work. I know someone who would probably be up for doing the work, but I don't have the budget yet. Just trying to figure out the best route forward.

There are other things to consider too like CAN protocol the same on Gen1 to Gen 2? CAN runs everything from your cruise control, to ABS, power steering, ect. If solidsnake11 could get the factory first gen electronics to run a turbo K24, it can be made to work. It is a matter of someone figuring it out.

[Teseo]

If it was plug n play, FA2.4 could be an fair option but will be more headache than solution. Would rather use that money to enhance/strengthen the actual FA20 (or go big with forged block). Idk mate, that idea is like paying child support for a foster kid

[alex87f]

Originally Posted by Tatsu333

The relevance is that with the 2nd gen ECU now being tunable, the "advantage" of going the short block swap route instead to have a tunable 1st gen ECU for further mods goes away.

That shifts the difficulty away from mating FA20 and FA24 mechanical parts together to the relative compatibility between 1st gen and 2nd gen ECU's with the 1st gen's other systems.

Which would be a bigger hurdle to overcome? I have no idea - I'm just hoping someone else might have more insight on the latter.



I have heard of EJ block swaps where they left the "step" of the smaller bore heads on the 2.5 block (I.E. they didn't enlarge the combustion chambers to match the bigger bore), but that just seems wrong to me for a number of reasons. I'm sure with a direct-injected, NA motor, the effect it would have on mixture swirl, etc. would be no good.

I guess a first step to assess the viability of the block swap would be to compare head gaskets from an FA24 and an FA20 to see whether or not things even line up, but I currently have other things to spend $200 on...LOL. FWIW, there seems to be a LOT of space between the bore and any other holes (coolant passages, etc.) in the FA20 head gaskets, but I can't even find any pictures of the FA24's head gaskets to compare.

If anyone on here happens to work at a Subaru parts counter and could just overlay the two for funsies that would be helpful...

I think somebody had worked out that the CR increased quite a bit with the FA20 head volume being relatively small compared to the FA24 cylinder. It was in the high 13's IIRC, which might be a problem, even with DI.



Also, with the piston being a "domed" unit on the FA24, you might run into intereference with a smaller diameter head, i.e. have to machine the head.

[Tcoat]

Originally Posted by Tatsu333

Just...shut up...LOL. Seriously though, I get where you're coming from. The ultimate power potential with other swap options is potentially much higher, but swapping in something from another manufacturer and running a standalone isn't anything I'm interested in at all.

I just want the 2nd gen's level of power (+headers and tune) with factory reliability and minimal headaches.




Ah - see, that is the kind of thing I hadn't thought about.

My experience with swaps is limited to 80's and 90's VW's, Honda's and Mazda's, back when things were much simpler (I'm old...LOL), and there was broad compatibility across different models / product lines.

So it is still likely a simpler solution to try and make the block swap work. I know someone who would probably be up for doing the work, but I don't have the budget yet. Just trying to figure out the best route forward.

As soon as you do any kind of swap the factory reliability goes away. People have had issues swapping the post facelift engines into their 13s so the 2.4 will never be a "plug and play" option.

Swapping just the block is not going to get you anything but a minor displacement increase. The head and everything else will still be restricted to the constraints of the 2.0. Be a massive expense for very little gain.

[Tatsu333]

Originally Posted by Tcoat

As soon as you do any kind of swap the factory reliability goes away. People have had issues swapping the post facelift engines into their 13s so the 2.4 will never be a "plug and play" option.

Swapping just the block is not going to get you anything but a minor displacement increase. The head and everything else will still be restricted to the constraints of the 2.0. Be a massive expense for very little gain.

Thanks for your input!

I hear what you're saying. Messing with anything, really, can cause reliability issues to some extent.

For me, when I'm talking "reliability", I mean compared to adding forced induction to an engine not designed for it, or swapping in a different manufacturer's engine and having to run a standalone.

RE: limitations of heads, etc., for a block swap, by all reports the FA20 heads can support a lot more flow / power, and the valve sizes are the same between it and the FA24 (though with a bit shorter intake valves - that could be because of an internal change in the heads, or to support higher lift).

According to folks running turbos, JR SC's, etc., the rest of the intake tract including the throttle body and intake manifold also has more than enough flow capacity.

The fuel injection system, etc. should also easily support the "minor displacement increase" (which at 20%, isn't really *that* minor considering we're talking motors of the same architecture in the same platform), since it's able to support the power levels of the CARB legal supercharging options.

Now, would it be as "optimized" as running the complete FA24 long block? No. It's possible, even likely, that a FA24/FA20 hybrid would have slightly less overall power potential than a complete FA24, but I would be going nowhere near its max potential anyway.

Would it be more reliable if it were possible to just plug in the complete motor, harness and ECU? Definitely.

Ultimately, with how low my average mileage is with working from home, I could probably just bolt on a Harrop or Edelbrock supercharger kit with a very mild tune, be ahead of the game in terms of power vs. the swap, and may never reach the point where long-term reliability is a concern. In the 14 years I drove my previous car, I only put on a little over 100,000 kms (about 62,500 miles). So far with my BRZ, I'm averaging about 500-600 kms per month.

That said, I plan to do some track days and other fun stuff with this car, so I might just be better off doing headers and a tune on the stock motor and spend more money on track time (and tires...LOL).

It's really just in the day-to-day, driving around town that I'm really envious of the improved torque in the 2nd gen, but maybe I won't care about that if I'm having fun tracking it more often? Who knows...

Thanks again for your input!

[Tatsu333]

Originally Posted by alex87f

I think somebody had worked out that the CR increased quite a bit with the FA20 head volume being relatively small compared to the FA24 cylinder. It was in the high 13's IIRC, which might be a problem, even with DI.

Also, with the piston being a "domed" unit on the FA24, you might run into intereference with a smaller diameter head, i.e. have to machine the head.

Thanks for your input! Yeah, that's why I feel it would be crucial to modify the heads to work with the new bore, and would probably also need custom pistons with valve reliefs in the right places for the FA20 heads.