2021 WRX and WRX STI - FA24???

[scooby24]

Originally Posted by Straight6

No doubt it can make and handle more power but my main point is that in its current form it was designed for the Ascent. I am curious to see what changes Subaru can make to make this engine fit the character of the STI. As it stands, it is pretty much a Subaru’s version of the Mazda’s 2.5T. An engine designed for an SUV, not a performance car, per say. But it definitely has the potential.

Then why'd they put it in the legacy?

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[Straight6]

"The engine was designed for torque, not horsepower," a Subaru spokesperson told The Drive, regarding the FA24's power output in the CVT-equipped Ascent. "It is as quick or quicker than the competition and quite good under full load."

https://www.thedrive.com/news/18562/...4-boxer-engine

The FA24 was designed with the same philosophy in mind as the new Mazda's 2.5T around SUV/larger vehicles in mind.

[WRXnick16]

I think a more accurate description would have been "tuned for torque".

The FA24 is essentially a bored out FA20 for more displacement. The overall engine design is the same. It has the potential to make at least the same horsepower as the FA20, but Subaru detuned it and tuned it for more torque while mating it to the CVT. The peak horsepower for both the FA20 & FA24 occurs at 5600 rpm. Peak torque is in the 2000-5000 rpm range for both. The added torque mostly comes from the extra displacement and tuning. The FA24 has the potential to make more torque (and therefore horsepower) at any given point in the powerband. The tuning , intake manifold, tmic, exhaust, etc. may account for the lower peak horsepower figure. I doubt Subaru would want to rate the Ascent's SUV FA24 with more horsepower than their "sporty" WRX. Just like the Forester XT's FA20 was detuned for less horsepower than the WRX, but produced the same 258 lb-ft of torque.

[4S-TURBO]

Originally Posted by scooby24

Then why'd they put it in the legacy?

They killed the 3.6 and replaced it with the FA24. Why did the Legacy get the 3.6 and not the FA20?

[subyski]

Originally Posted by scooby24

Then why'd they put it in the legacy?

Because Outback. The Outback is their bread and butter and the Legacy is just following behind.

[SeeeeeYa]

Originally Posted by subyski

Because Outback. The Outback is their bread and butter and the Legacy is just following behind.

And, as far as I’m concerned, a great choice.

Street cars should have a torquey engine.

Race cars can benefit from both, depending on the venue. Only race-only cars need more high end horsepower.

Having said that, the question is... what kind of car is the STi?? And, which engine will be in it when Subaru takes it to the ‘ring.

[WRXnick16]

Originally Posted by SeeeeeYa

Having said that, the question is... what kind of car is the STi?? And, which engine will be in it when Subaru takes it to the ‘ring.

I wouldn't be surprised if the USDM STI gets the larger bore/displacement FA24 even if the JDM version gets the FA20.. just like we got the EJ257 instead of the EJ207.

The FA24 with a EL header & twin scroll turbo could be quite torquey depending on the turbo size.. especially if the short gearing is carried over from the current STI drivetrain.

[Straight6]

Originally Posted by WRXnick16

I wouldn't be surprised if the USDM STI gets the larger bore/displacement FA24 even if the JDM version gets the FA20.. just like we got the EJ257 instead of the EJ207.

The FA24 with a EL header & twin scroll turbo could be quite torquey depending on the turbo size.. especially if the short gearing is carried over from the current STI drivetrain.

I have a feeling that the next gen WRX for the US market will stick with the FA20 making around 280 hp and the STI will get the FA24 with around 320 hp.

[Dorian7]

Prime motoring has already tuned an FA24 swapped crosstrek with an FP blue turbo and ethanol and got 500WHP/484TQ on a stock motor. Apparently they maxed the MAF and ran out of fuel.

[WideBody]

Originally Posted by Brahmzy

Nonsense about the FA24 being an SUV engine, or designed for more torque, lol.
It’s a freakin engine. It can be specifically tuned and have specific components that lend it to differing workloads. The new Legacy, for instance, or an STI.
It’s got craploads of torque because it’s a direct injection, turbo, large displacement motor, lol. It is a PERFECT for an STI.

Unless they can somehow make it rev higher, it's going to be a miserable STI engine, regardless of the torque numbers. What I always wanted was a STI with a sub 6000RPM redline

[WRXnick16]

Originally Posted by WideBody

Unless they can somehow make it rev higher, it's going to be a miserable STI engine, regardless of the torque numbers. What I always wanted was a STI with a sub 6000RPM redline

It has the potential to rev just as high as the FA20 in the WRX or BRZ since it maintains the same 86mm stroke and overall engine design. It just depends on what Subaru decides to do. I wouldn't hold my breath for anything over 7,000 rpm..

FA redlines:
Forester XT (CVT) FA20F: 6,000 rpm
WRX FA20F: 6,700 rpm (CVT is 6,500 rpm)
BRZ FA20D: 7,400 rpm
Ascent/Outback (CVT) FA24F: 6,000 rpm

EJ redlines:
USDM STI EJ257: 6,700 rpm (same as wrx - not a high revving engine)
JDM STI EJ207: 8,000+ rpm (depending on the year/model)

The redline limitation of the WRX's FA20F & STI's EJ257 both involve head flow (ports, cams, valve springs, intake manifold, etc.) and a few other things. The EJ257 is limited by its UEL header. The FA20 is limited by its smaller turbo. The oiling system also isn't optimal for high rpms. However, these are all things that could be fixed if Subaru chose to..

Both engines have a relatively small stroke that will keep piston speeds safe at higher rpms.. just look at the EJ207's 8k+ rpm redline. Just for fun, here's an example of a EJ207 revving to 12,000 rpm.
https://www.thedrive.com/tuned-af/17...s-to-12000-rpm

It would be amazing if Subaru designed a "frankenstein" engine based on the existing FA platforms..

• Head & intake manifold design from the BRZ's FA20 = more power & higher redline
• Toyota's D4S dual injection from the BRZ = more efficient & eliminate carbon build-up
• A good "STI" cam design that falls somewhere between the WRX & BRZ's (designed for a turbocharged engine) = more power & higher redline
• A beefed up version of the Ascent's FA24 short block (it's already stronger than the WRX's FA20F) = more displacement & withstand more torque
• A good EL header with a larger twin scroll, ball bearing turbo = more power & higher redline

But I'm dreaming at this point. That would easily produce an engine capable of 350-400 hp in stock form.. and probably close to 400 whp with just adding flex fuel.

[4S-TURBO]

The FA24 is the only engine they could use that will push output over the 300 hp threshold with all the variables our market has in addition to the engine design limitations and overall load it sees at the price point. An FA20T that can spin to BRZ FA20 levels would be awesome but could Subaru justify pushing output beyond 300 hp on 91 pump when they already have the FA24? Just look at Porsche's boxer 4 specs on their 2.0 and 2.5 engines. Doubtful Subaru is besting Porsche specs.

[neg_matnik]

Originally Posted by Straight6

"The engine was designed for torque, not horsepower," a Subaru spokesperson told The Drive, regarding the FA24's power output in the CVT-equipped Ascent. "It is as quick or quicker than the competition and quite good under full load."

https://www.thedrive.com/news/18562/...4-boxer-engine

The FA24 was designed with the same philosophy in mind as the new Mazda's 2.5T around SUV/larger vehicles in mind.

Jumping in to say that FA24 and Mazda's 2.5 are polar opposite in terms of geometry: 94 mm bore vs 89 mm and 86 mm stroke vs a whopping 100 mm.
We have a short(ish) stroker vs a long stroker; the long stroker is better suited for SUV-type load/usage.
The short stroker? Not so much.
As I said from the early days of FA24 news and rumors, Subaru is the only manufacturer that's using a 4-cyl short stroker for SUV duty; it's highly unusual/atypical.
Just my .02c, please carry on.

[neg_matnik]

Originally Posted by WRXnick16

It has the potential to rev just as high as the FA20 in the WRX or BRZ since it maintains the same 86mm stroke and overall engine design. It just depends on what Subaru decides to do. I wouldn't hold my breath for anything over 7,000 rpm..

FA redlines:
Forester XT (CVT) FA20F: 6,000 rpm
WRX FA20F: 6,700 rpm (CVT is 6,500 rpm)
BRZ FA20D: 7,400 rpm
Ascent/Outback (CVT) FA24F: 6,000 rpm

EJ redlines:
USDM STI EJ257: 6,700 rpm (same as wrx - not a high revving engine)
JDM STI EJ207: 8,000+ rpm (depending on the year/model)

The redline limitation of the WRX's FA20F & STI's EJ257 both involve head flow (ports, cams, valve springs, intake manifold, etc.) and a few other things. The EJ257 is limited by its UEL header. The FA20 is limited by its smaller turbo. The oiling system also isn't optimal for high rpms. However, these are all things that could be fixed if Subaru chose to..

Both engines have a relatively small stroke that will keep piston speeds safe at higher rpms.. just look at the EJ207's 8k+ rpm redline. Just for fun, here's an example of a EJ207 revving to 12,000 rpm.
https://www.thedrive.com/tuned-af/17...s-to-12000-rpm

It would be amazing if Subaru designed a "frankenstein" engine based on the existing FA platforms..

• Head & intake manifold design from the BRZ's FA20 = more power & higher redline
• Toyota's D4S dual injection from the BRZ = more efficient & eliminate carbon build-up
• A good "STI" cam design that falls somewhere between the WRX & BRZ's (designed for a turbocharged engine) = more power & higher redline
• A beefed up version of the Ascent's FA24 short block (it's already stronger than the WRX's FA20F) = more displacement & withstand more torque
• A good EL header with a larger twin scroll, ball bearing turbo = more power & higher redline

But I'm dreaming at this point. That would easily produce an engine capable of 350-400 hp in stock form.. and probably close to 400 whp with just adding flex fuel.

Yes, FA20 and FA24, share the same stroke and same rod length. So, rod-to-stroke ratio is identical; except that FA24 has larger and, potentially, heavier pistons.
So, I'd say FA24 may not want to rev quite as well as FA20 depending on how much heavier its pistons are.

[WRXnick16]

Originally Posted by neg_matnik

Jumping in to say that FA24 and Mazda's 2.5 are polar opposite in terms of geometry: 94 mm bore vs 89 mm and 86 mm stroke vs a whopping 100 mm.
We have a short(ish) stroker vs a long stroker; the long stroker is better suited for SUV-type load/usage.
The short stroker? Not so much.
As I said from the early days of FA24 news and rumors, Subaru is the only manufacturer that's using a 4-cyl short stroker for SUV duty; it's highly unusual/atypical.
Just my .02c, please carry on.

Well put. SUV engines are typically "under-square" (larger stroke than bore), but Subaru may be somewhat limited with stroke in terms of packaging the boxer engine under the hood. They could always reduce the rod length, but of course that decreases the rod/stroke ratio, increases piston side loading & friction, and decreases combustion efficiency..

Over-square (shorter stroke) engines are typically performance oriented which is why it's odd to see them in an SUV. Longer strokes are more common in SUVs and trucks to provide low RPM torque and improved towing capacity. The FA24's small turbo and compression ratio probably help compensate for this.

Talk of boxer engines and bore/rod/stroke ratios made me curious about the GT3's engine and its 9k rpm redline.. it's very similar to the EJ257's bore stroke.

GT3: 102mm bore & 81.5mm stroke = 1.25 bore/stroke ratio
EJ257: 99.5mm bore & 79mm stroke = 1.26 bore/stroke ratio
EJ207: 92mm bore & 75mm stroke = 1.23 bore/stroke
FA24: 94mm bore & 86mm stroke = 1.09 bore/stroke ratio

Unfortunately, I couldn't find anything on the GT3's rod length or rod/stroke ratio.
EJ257 rod length = 130.5mm = 1.65 rod/stroke ratio
EJ207 rod length = 130.5mm = 1.74 rod/stroke
FA24/FA20 rod length = 129.3mm = 1.50 rod/stroke ratio

I'd also be curious what the longest stroke boxer engine in history is..

[WRXnick16]

Originally Posted by neg_matnik

Yes, FA20 and FA24, share the same stroke and same rod length. So, rod-to-stroke ratio is identical; except that FA24 has larger and, potentially, heavier pistons.
So, I'd say FA24 may not want to rev quite as well as FA20 depending on how much heavier its pistons are.

Anything is possible depending on what Subaru does.. The E257 has 99.5mm pistons. The EJ207 has 92mm pistons with a 8k+ rpm redline. The GT3 has 102mm pistons with a 9k rpm redline. Anything is possible with enough money and engineering

[Dorian7]

Here is the dyno chart, looks like they ran it up to 6400rpm

[user1029]

^^^must be one fun Crosstrek

[WRXnick16]

Originally Posted by 4S-TURBO

Just look at Porsche's boxer 4 specs on their 2.0 and 2.5 engines. Doubtful Subaru is besting Porsche specs.

The Cayman's 2.5L engine is interesting..

It has a very large bore/stroke ratio (102 mm bore & 76.4 mm stroke = 1.34) even compared to the GT3 (1.25). It even has a shorter stroke than the GT3 (76.4 vs 81.5 mm). Porsches tend to have relatively long connecting rods which would also give it a large rod/stroke ratio. The Cayman even has a dry sump oil system! These are all traits of high revving performance engines.. yet it has a redline of "only" 7,500 rpm (compared to the GT3's 9,000 rpm). Kind of reminds me of the EJ257

I'm guessing that it compromises with a relatively small variable vane turbo as its peak torque is achieved between 1,900 - 4,500 rpm. The compression ratio is a bit lower than expected at 9.5:1 compared to the FA20/FA24's 10.6:1.

The GTS version does make a bit more power (365 vs 350 hp) thanks to a higher redline, larger compressor wheel & 18.1 psi of boost. But it definitely seems like they left some power on the table. I bet it has an amazing powerband with a flat torque curve.

Edit: Found dyno charts showing said powerband - look at the table-top torque curve on the GTS!

The 718 GTS gets a slightly larger turbocharger than S model cars allowing power to hold out better up top where the S starts to fall off. Our test car spun the rollers to the tune of 345 HP and 328 TQ to the wheels in stock form. With a slight increase in boost pressure, we saw results of 378 HP and 353 TQ to the wheels. As you can see in the dyno graph below, power still holds on beyond 6000 RPM whereas the S above starts to see torque tail off due to the smaller compressor wheel.

https://www.cobbtuning.com/porsche-7...ssport-tuning/

Power is still climbing on the GTS.. it would be interesting to see how far the stock turbo could carry the power up top. Either way it looks like Porsche's goal was a flat torque curve with plenty of power throughout the entire rev range. Impressive.

[SeeeeeYa]

Subaru can do the same thing... if they want to.

[WRXnick16]

Originally Posted by SeeeeeYa

Subaru can do the same thing... if they want to.

Exactly.. and we can keep dreaming based on past experience

The S209 is already rated at 341 hp and we know that it could make more.

A forged EJ257 block + EJ207 heads/cams + EJ207 equal length header + a larger twin scroll, ball bearing turbo to shift the powerband to the right (closer to the EJ207's 8,000 rpm redline) = a perfect recipe for > 350 hp.

But I assume those changes would have made the certification process harder and more expensive for Subaru.. not worth it for a limited production vehicle.

Maybe Subaru will surprise us with a fresh start on the next STI engine. We know that the FA engine is more efficient than the EJ257 and has the potential to be great. I suspect that we'll initially get something watered down so that they don't exceed the S209's power level right out of the gate. They'll probably bump the power more during a mid-cycle refresh and hopefully give us another S series.

[SeeeeeYa]

What with SGP, new turbo engines, new upscale models, and the onslaught of the competition... it would be a stroke of genius for Subaru to release an STi that brought shock and awe to the reviews.

It would put the spotlight on the brand. A brand good enough and worthy enough to deserve the spotlight. Sales would climb, and climb. A new image would emerge.

Imagine that.

It’s happened before. It worked. It would work again.

[4S-TURBO]

[ejicon]

Originally Posted by WRXnick16

Exactly.. and we can keep dreaming based on past experience

The S209 is already rated at 341 hp and we know that it could make more.

A forged EJ257 block + EJ207 heads/cams + EJ207 equal length header + a larger twin scroll, ball bearing turbo to shift the powerband to the right (closer to the EJ207's 8,000 rpm redline) = a perfect recipe for > 350 hp.

If this were to happen, you'd have 200 VERY unhappy campers in 2021

[gathermewool]

Originally Posted by ejicon

If this were to happen, you'd have 200 VERY unhappy campers in 2021

**** them!