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)

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(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.