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Discussion Starter · #1 · (Edited)
Are there any differences between the FB20D and FB25D besides the bore size?
BoreStrokeDisplacementEngine
84 mm
90 mm
1.995 L
Subaru 152 hp FB20D 350 lbs
94 mm
90 mm
2.498 L
Subaru 182 hp FB25D 500 lbs

Obviously there is a difference in weight, but I presume that is mostly the block size.
This website states that the FB25 is more reliable than the FB20.
Overall, the FB 25 is solid and probably more reliable than the FB20.

The following quotes from this website imply that the FB25 is substantially improved over the FB20, however it seems to me that the comments are applicable to the FB20B & FB25B. I don't know if they are also applicable to the FB20D & FB25D.

FB20: Since Subaru wanted this engine to achieve excellent efficiency they used a lightweight rotating assembly and a high compression ratio. This increased thermal efficiency which translated into a 2+ MPG increase. Those lightweight pistons, however, are known are having poor oil rings. Poor oil rings results in excessive oil consumption as mileage increases. Other than the oil rings the FB20 is a pretty reliable little engine.
Subaru designed the FB for efficiency and as such didn’t utilize a very strong bottom end. The cars that use the FB20 aren’t performance oriented at all either. For this reason modifying the FB20 engine is pretty much never done.
FB25: Good thing that the FB25 engine does not suffer behind the trails of the FB20 engine. The latter has issues regarding high oil consumption, which was addressed by Subaru and improved for the follow-up engine under the FB25 name. However, there are still issues that might affect the reliability and overall lifespan of the machine, but it might be due to external factors such as age, mileage, and the standard wear and tear items. The maintenance-free timing chains and peripheral components are designed to withstand long periods. It tends to last the same as the engine itself. So if your machine is slowly deteriorating, the chances are that the components inside are also under the same sentiments.
 

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2021 Subaru Impreza 5-Door Sport 5MT
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Are there any differences between the FB20D and FB25D besides the bore size?
BoreStrokeDisplacementEngine
84 mm
90 mm
1.995 L
Subaru 152 hp FB20D 350 lbs
94 mm
90 mm
2.498 L
Subaru 182 hp FB25D 500 lbs

Obviously there is a difference in weight, but I presume that is mostly the block size.
This website states that the FB25 is more reliable than the FB20.
Overall, the FB 25 is solid and probably more reliable than the FB20.

The following quotes from this website imply that the FB25 is substantially improved over the FB20, however it seems to me that the comments are applicable to the FB20B & FB25B. I don't know if they are also applicable to the FB20D & FB25D.
FB25D has a larger bore which will likely add your increase in weight due to piston size. The FB20 also uses a cooling jacket spacer to help with fuel economy. Cylinder wall thickness seems to be the same. The FB25's which we build at SIA also use an MCV cooling system rather than your traditional thermostat. Dimensionally you'll find most FA/FB motors are the same size, just minor internal differences. In regards to reliability, I'd venture to say the over square nature of the engine is fighting its overall longevity.
 

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Discussion Starter · #3 ·
Install FB25D in the Impreza
This thread went from Feb 9-20, 2020 before Subaru announced the FB25D was going into the Sport and Limited trim of the Crosstrek,

One forum member replied
Keep in mind that engine swaps are not a simple thing anymore. Maybe it will fit easily (probably could), but then you will need to fit it to the ECU. also, it will not be a legal conversion, so you won't be able to pass emissions testing in most places.
Do you believe the FB25D could be put into the Impreza at the factory?
 

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2021 Subaru Impreza 5-Door Sport 5MT
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Install FB25D in the Impreza
This thread went from Feb 9-20, 2020 before Subaru announced the FB25D was going into the Sport and Limited trim of the Crosstrek,

One forum member replied


Do you believe the FB25D could be put into the Impreza at the factory?
Being the Impreza and Crosstrek are the exact same platform. I've been wondering why we haven't already done it lol.
 

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Discussion Starter · #5 · (Edited)
Being the Impreza and Crosstrek are the exact same platform. I've been wondering why we haven't already done it lol.
Well you can purchase the 5-door Impreza Sport trim with 5MT. I assumed if the 5-door Impreza Sport & Limited trim came with the FB25D engine you would have to offer the 5MT with the base and premium trim only.

The inclusion of the FB25D engine seems to have done wonders for Crosstrek sales. Crosstrek US sales are at 84,126 by the end of July 2022, and they were just 87,139 at the end of July 2018 which was the first year of the 2nd generation. I think that is pretty unprecedented for the 5th year of a generation.

For the first seven months of 2022 US sales of these four models is down 9.7%. I know that is good compared to the other four models that are imported from Japan (down 25%). However, it would be nice if the Impreza could get a boost. This is an Impreza forum!😀
+6.0%​
Ascent​
-15.4%​
Outback​
-7.4%​
Impreza​
-8.8%​
Legacy​
-9.7%​
4 Models​
 

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Yeah the power delivery on the 2.5 is so much better suited in these cars. They just mesh really well. But we both know if they brought the 2.5 to the Impreza the manual would be gone. The manual transmission just doesn't align with their new marketing safety needs since they can't say it comes standard with "Eyesight".
 

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The 152 hp FB20D has a power to weight ratio of ~20.6 in an Impresa Sport. A FB25D @ 182 hp would increase that to a not insignificant ~18.0. However, I'm wondering how an engine weighing additional 150 lbs would affect the Impreza's handling.
 

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Discussion Starter · #8 ·
My older 2007 Impreza is short stroke instead of the modern ones which are long stroke. I guess they switched to get more fuel economy.

Bore​
Stroke​
Displacement​
Ratio​
Engine Name​
84​
90​
1,995​
0.93​
FB20D 152 hp​
84​
90​
1,995​
0.93​
FB20B 148 hp​
99.5​
79​
2,457​
1.26​
EJ25 174 hp 2007 Impreza​
 

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Discussion Starter · #9 ·
The 152 hp FB20D has a power to weight ratio of ~20.6 in an Impresa Sport. A FB25D @ 182 hp would increase that to a not insignificant ~18.0. However, I'm wondering how an engine weighing additional 150 lbs would affect the Impreza's handling.
As I understand it the Crosstrek is virtually the same vehicle as the Impreza from a drivetrain point of view. They did it for the Crosstrek.
 

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2022 Subaru Impreza Sport CVT
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Being the Impreza and Crosstrek are the exact same platform. I've been wondering why we haven't already done it lol.

I heard it has to do with a difference between the firewalls of the vehicle. It apparently is the same reason why the Impreza does not have a 6 spd option but the Crosstrek gets it. Never was given a source for this, though
 

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I heard it has to do with a difference between the firewalls of the vehicle. It apparently is the same reason why the Impreza does not have a 6 spd option but the Crosstrek gets it. Never was given a source for this, though
I don't have the answer, but I do get to see how much cost plays in every decision that's made here. We count pennies per part. The changes make more sense for the Crosstrek because we sell more of them. In regards to JGR, the torque curve will give you a much better driving experience. The FB20 makes peak HP at peak RPM with little torque throughout the curve. The FB25 would provide a much better driving experience IMO.
 

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Discussion Starter · #12 · (Edited)
I don't have the answer, but I do get to see how much cost plays in every decision that's made here. We count pennies per part.
Well obviously we don't appreciate the amount of record keeping that goes into the cost analysis. But to have a 50% drop in sales in only three years is pretty startling. It may very well be that the profit margin is so much higher on the Crosstrek, it pays to simply let the Impreza limp along.

Crosstrek
Impreza (both 4&5 door)
127,466​
2021​
34,791​
119,716​
2020​
43,628​
131,152​
2019​
66,415​
144,384​
2018​
76,400​
110,138​
2017​
86,043​

Projections for future sales of the Impreza when they moved the Gen 5 production to Indiana were very high. Subaru wants to best the Impreza’s prior sales recordof 81,799, set in 2012, possibly hitting 90,000-100,000 annual deliveries with the new model. - Dec 19, 2016
I realize that forecasts are by nature extremely optimistic, but sales dropped 20,000 even before the pandemic hit. I also realize that article was written two months before the startling Feb 28, 2019 press release: "$35,000 Tesla Model 3 Available Now".

BTW - the 81,799 number in 2012 would include the WRX since that was not a seperate model. So counting only Imprezas, there were 68,175 US sales in 2012 which was handily beaten by the 2017 generation 5 sales.
 

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As I understand it the Crosstrek is virtually the same vehicle as the Impreza from a drivetrain point of view. They did it for the Crosstrek.
That's true, but the Crosstrek's handling is already compromised by it's 3.6" of additional ground clearance.
 

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Discussion Starter · #14 ·
Since it doesn't take a genius to propose following the Crosstrek lead and replacing the Sport and Limited trim engines in the Impreza with FB25D engine we must assume Subaru executives have considered and rejected the idea. It is very possible that in this microchip limited environment, they are just as happy to see the Impreza sales reduced to a tiny percentage of what they were in 2017. All three AWD cars are selling at a rate much lower than 2021 (for first 7 months).

-7.4%​
Impreza​
Indiana​
-8.8%​
Legacy​
Indiana​
-47.3%​
WRX​
Japan​
 

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......

Do you believe the FB25D could be put into the Impreza at the factory?
No. The days of a "special order engine" are loooong past. In order to sell a separate engine option, it has to be tested by the government, fuel economy, emissions, as well as collision testing, before it can be approved. The cost of the engineering required alone will run into the millions, then a few million more for the government approval. In order to justify the cost, they must sell a fairly large number of units to pay for the outlay. So, for an inexpensive economy car, it's just not feasible, especially when Subaru also sells the WRX, and they don't want to cut into the sales of that model.
 

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Discussion Starter · #16 · (Edited)
So, for an inexpensive economy car, it's just not feasible, especially when Subaru also sells the WRX, and they don't want to cut into the sales of that model.
I don't think boosting an Impreza 5 door from 152 hp to 182 hp is going to threaten sales of a turbocharged 271 hp WRX.

What do you think would jolt Impreza sales if not a bigger engine? Six speed manual transmission? Wheel Cladding?

Average monthly sales in 2022 for all four Subaru cars are pretty low especially considering that Subaru has ~600 dealers in the US.
Avg Monthly 2022
Car
2,365​
Impreza (4&5 door)​
1,992​
Legacy (4 door)​
1,249​
WRX (4 door)​
238​
BRZ (2 door)
37,743​
SUVs
 

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I don't think boosting an Impreza 5 door from 152 hp to 182 hp is going to threaten sales of a turbocharged 271 hp WRX.

What do you think would jolt Impreza sales if not a bigger engine? Six speed manual transmission? Wheel Cladding?

Average monthly sales in 2022 for all four Subaru cars are pretty low especially considering that Subaru has ~600 dealers in the US.
Avg Monthly 2022
Car
2,365​
Impreza (4&5 door)​
1,992​
Legacy (4 door)​
1,249​
WRX (4 door)​
238​
BRZ (2 door)
37,743​
SUVs
The current body style is starting to get old now. Its to be expected to see a decline in sales this late into the design. I swear to gaaaawwwwwd if they add side cladding to the Impreza I'm going to lose my mind lol.

I do think a bump in power would help the Impreza. Especially if we can get more power and better fuel economy (like the Crosstrek experienced).
 

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Discussion Starter · #18 · (Edited)
The current body style is starting to get old now. Its to be expected to see a decline in sales this late into the design.
You can read reviews from 15 years ago, and their biggest criticism is the car is fuddy duddy. Obviously that is the primary reason the exact same body as a Crosstrek outsells the Impreza by 5 to 1.

I do think a bump in power would help the Impreza. Especially if we can get more power and better fuel economy (like the Crosstrek experienced).
Every review you read of the Impreza, from Consumer Reports and on, says that the Impreza delivers AWD with a reasonable power for the best price in America. It also has the best fuel economy for AWD and naturally aspirated non hubrid vehicle in America. For people who don't like CVT they maintain the 5MT.

But sales are dropping like a stone. Since the 2023 model year also has no changes, we can expect sales to go even lower. The high priced gasoline seems to have no effect. The bottom line is the
  • 2023 Crosstrek Sport costs $3105 more than the 2023 Impreza 5 Door Sport with CVT,
  • 2023 Crosstrek Limited costs $2305 more than the 2023 Impreza 5 Door Limited.
A big factor (but not the only one) is the extra 30 hp.

But one huge factor is no matter how similar they look to us, the EPA classifies the Impreza as a car and the Crosstrek as a type of light truck. Corporate Average Fuel Economy (CAFE) standards for light trucks are 26% lower than for cars. In four years they are both going to increase but light trucks will be 29% lower than for cars. Going from the 2.0L to 2.5L naturally aspirated engine makes a relatively small decrease in fuel economy compared to going from a 2.5L naturally aspirated to a 2.4L turbocharged engine. However, it is possible it is just enough to mess up CAFE requirements for the Impreza. Only Subaru has that data.

It is even possible that the 20% increase in Corporate Average Fuel Economy (CAFE) requirements for passenger cars are severe enough that Subaru will simply discontinue making all cars in four years. I'm talking about the Legacy, Impreza, WRX, and BRZ. They are a relatively small percentage of the Subaru business, and it will be much easier to stay in compliance with just SUVs and EVs. For 2022 percent of Subaru US sales for cars are:
5.4%​
Impreza​
4.6%​
Legacy​
2.9%​
WRX​
0.6%​
BRZ​

The CAFE standards for SUVs are much lower and they will only increase by 15% over the next four years. I think in order to do that Subaru will still need a new halo vehicle, but it will have to be an EV. They are talking about an electric STI.
 
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