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  • - Boxer engines.

  • One of the most iconic automotive sounds out there

  • (car engine rumbling) is the rumble

  • of that Flat 4 EJ powering all four wheels

  • of the Subaru WRX STI.

  • It's been the heart of the STI for 26 years

  • and now

  • Subaru has thrown it out.

  • And they're putting in an engine from an SUV.

  • That burdens your bridges, chaps your burn,

  • tans your hide.

  • It just plain ticks you off.

  • Oh, I have good news for you.

  • This engine is the best engine the STI has ever had.

  • And today I'm gonna show you exactly why.

  • We're gonna look at this new FA24 engine

  • and find out where it's hiding all

  • that buff Boxer potential.

  • Don't believe Subaru can turn a mom mobile motor

  • into a Flat 4 phenom? Well, I guess we just got to show you.

  • Let's go

  • (dramatic upbeat music)

  • (buzz)

  • A huge thanks once again, to our friends over at Keeps

  • for sponsoring another episode of Bumper to Bumper.

  • I'm gonna be straight with you guys.

  • I have a weird shaped head under this hat and all this hair.

  • So I need my hair, without it, I'd look something like this.

  • (child shrieking)

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  • And if you still have hair

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  • hidden by all that lush beautiful hair, just like I do.

  • Can you tell how weird this head is?

  • You can even visit a doctor online

  • and get hair loss medication delivered right to your door

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  • You never need to leave your house,

  • which is pretty good right now. Avoid the dreaded comb-over

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  • Go to keeps.com/b2b

  • or click the link in the description

  • to receive a special offer on keeps hair loss treatments.

  • That's K-E-E-P-S.com/B-2-B.

  • Thank you for supporting the companies

  • that support us here at Donut.

  • (beep) Now if you don't know,

  • the rumors are all but confirmed

  • that the new Subaru WRX STI is coming in 2022

  • with the revised version of the FA24 engine,

  • currently in the Subaru Ascent.

  • And supposedly the STI will make a total 400 horsepower

  • to the wheels.

  • Now to put that in quick perspective,

  • that's 90 more than the current STI,

  • 60 more than the most powerful STI

  • and 140 more than what the Ascent makes right now.

  • Now, quick note before we get too deep,

  • we're going to be saying FA and EJ a lot today.

  • Now, if you don't know what those mean,

  • it's simply the engine code that Subaru uses

  • to identify their Boxer power plans.

  • EJs were the two-liter and two and a half liter engines

  • that came in the WRX and the STI

  • all the way from the beginning

  • and the FA engines are the new platform.

  • These engines don't have the same "Suby rumble",

  • but it's theoretically got more power.

  • So where is that extra power coming from?

  • Well, let's take a look.

  • (upbeat music)

  • One of the main things that's new for the FA engines

  • is direct fuel injection,

  • as opposed to the EJs' port injection.

  • Now port injection is when your fuel injector

  • is placed in the intake manifold

  • upstream of the intake valve

  • and the air and fuel mix there

  • before they enter the cylinder.

  • Now, the upside of that, is that the air and fuel

  • have a longer time to mix before they enter

  • into the cylinder.

  • But the downside is that it's less precise

  • on the air:fuel ratio

  • because you're losing a little bit of fuel

  • as it sticks to the intake valve.

  • Now direct injection means that fuel is shot directly

  • into the cylinder. It's injected directly,

  • just like the spark is.

  • And the fuel was fired much later and much more precisely

  • than port injection and it's fired

  • at a much higher pressure.

  • And there are plenty of benefits from this.

  • Now the system is more efficient,

  • meaning better fuel economy. That's good.

  • And also it cools the cylinder

  • because it sprays a nice mist of fuel on the cylinder walls.

  • And that lowers the temperature of the wall.

  • Reducing the chance of pre-ignition or engine knock

  • that might occur from the combustion chambers heat.

  • Think about that heat, the cylinders get so hot

  • that they can sometimes when you inject fuel in

  • cause it to auto ignite, it's not good.

  • It creates knock, ping.

  • You don't want it.

  • You don't want it. (beep)

  • Ultimately direct injection is better for fuel efficiency

  • and engine health,

  • which overall let's the engine safely hold more power.

  • But there are some downsides to it.

  • There's always good and bad.

  • Direct injection needs the engine to be warm,

  • to atomize fast enough and mix with the air

  • and overcome that they need a lot more fuel on a cold start.

  • Trust me, direct injection is the way to go,

  • but if you're not sold on it,

  • then I got some good news for you. Okay.

  • If you will please indulge me

  • and take a quick trip over to

  • the speculation zone. (soft sci-fi music)

  • In the current Subaru BRZ,

  • also the Toyota GT86.

  • Toyota's fancy D4-S fuel system uses both port

  • and direct injection.

  • And it's actually a very simple system.

  • The direct injectors are strong enough

  • to run the engine at high RPM,

  • but for better startup,

  • the engine splits the work between the two sets of injectors

  • at cold start.

  • Literally the best of both worlds.

  • And this version of the D4-S system,

  • isn't in the FA24 engine currently,

  • but it could be added assuming the STI

  • isn't going to use the same intake manifold.

  • Now our buddies over at Prime Motoring in New Jersey

  • have been tuning Subarus for years

  • and they took a closer look at the existing FA24.

  • And they had been tinkering with it

  • just to see what the new STI is going to be capable of.

  • And with a new intake manifold,

  • the FA24 could totally use this D4-S system from the BRZ.

  • But that's not the only promising thing

  • they found in the new engine.

  • The block and head themselves has some hidden heft as well.

  • (upbeat music)

  • Even though it's still a Flat 4

  • and it's got about the same displacement

  • as the old EJ257, the FA24 is 100% new engine.

  • And Subaru has had a lot of time

  • to improve on how they make power.

  • The cylinder head on this new engine

  • has more of a straight shaft for airflow

  • than the EJ had with its more dog-leg path

  • for the air to go through.

  • You know what a dog leg is. It looks like this.

  • It looks like a Ben Cheeto.

  • You may not think that these little angles

  • could slow down free flowing air,

  • but in an engine and especially in a turbocharged engine,

  • a free flowing path is super duper important.

  • Now, if the pathway is causing air to bounce around

  • creating turbulence and pressure pockets,

  • the air can only go so fast.

  • And at high revs,

  • it can't get air into the cylinder fast enough.

  • So we always want a freer flowing head, to get us more air

  • because we know our famous equation,

  • more air plus more fuel equals more power.

  • Now we've already got more fuel from the direct injection

  • and now we've got more air.

  • But for every engine, there's a breaking point.

  • A point where if you put too much air in,

  • and you put too much fuel in,

  • you're gonna get too much combustion

  • for the block to handle.

  • And the main thing about an engine's block

  • is that it's got to be strong.

  • Those cylinder walls have to be thick enough

  • to withstand the pressure that the engine is gonna make

  • or else,

  • Well, there's no easy way to say this.

  • Your engine will blow up.

  • Let's say with a turbocharged engine,

  • you're making 15 pounds of boost or 15 PSI of pressure.

  • That's pressurized air that goes into this cylinder

  • on the intake shaft.

  • And when the piston is fully down

  • that's the most space available,

  • and then the intake valve closes

  • and that air goes all the way back up

  • and it gets compressed

  • as the piston gets pushed back up again.

  • And an engine let's say with a 10:1 compression ratio,

  • you're looking at roughly 150 PSI.

  • That is a lot of pressure,

  • but that's not a lot of pressure

  • compared to what happens next.

  • The spark.

  • Once that spark hits that compressed air and fuel mixture,

  • it ignites, it creates a combustion.

  • And that pressure jumps to anywhere between

  • 300 and 1000 PSI, forcing that piston all the way back down.

  • So the cylinder walls have to withstand that pressure,

  • right at the moment of combustion,

  • getting forced all the way down all the way up

  • and that's happening thousands and thousands of times

  • a minute.

  • So how does the FA24 handle that?

  • Well, it's got thick (beep) cylinder wall.

  • And not only does it have thicker cylinder walls

  • than it's EJ bro bro, it's got more cylinder support

  • molded into the casting.

  • And in an engine that can take more pressure.

  • You can up the boost or up the compression

  • to make more power,

  • but cylinder walls aren't the only thing

  • that needs to be beefy to make power in an engine.

  • And lucky for us Suby-loving Boxer boys,

  • the FA24,

  • just like Arby's sandwiches.

  • It's got more beef inside.

  • Has more beef- Okay stop it.

  • (upbeat music)

  • The FA engine has been around a little while

  • and it's gotten its fair share of complaints,

  • but in a way, that was kind of the point.

  • Subaru used the FA20 DIT as a test bed

  • for what the FA24 would eventually become.

  • And inside their SUV engine

  • are some really over engineered parts.

  • It's almost as if they were designing this engine

  • with something else in mind.

  • Now the connecting rods were a point of failure on the FA20.

  • All that pressure that we talked about earlier,

  • pushing down on the piston.

  • Well, it also pushes on the connecting rods,

  • which connect the pistons to the crankshaft.

  • Now this is where the direction of our energy changes

  • from the pushing force of the combustion

  • to the rotational force.

  • Now that connecting rod is attached to the crankshaft

  • off center

  • and it's attached to the piston on a pivoting pin.

  • So as it gets pushed down, it rotates the crankshaft,