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Old 02-01-2011, 09:27 AM   #1
rsholland
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Default C&D examines new FB engine

http://www.caranddriver.com/news/car...-four-car_news

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Examining Subaru’s New FB-series Flat-Four
It still displaces 2.5 liters and makes 170 horsepower, but Subie’s flat-four is newer than you’d think.
BY K.C. COLWELL
January 2011


The EJ-series flat-four has ruled the Subaru universe since it debuted in the 1989 Legacy. In today’s most desirable Subarus, a 2.5-liter EJ makes anywhere from 224 to 305 horsepower with belt-driven dual overhead cams and a turbocharger. Lowlier Subie models have a SOHC EJ of identical displacement that makes 170 horses. Of course, those desiring more cylinders can have a 3.6-liter pancake-six making 256 horses in the top-dog Legacy and Outback, and the Tribeca is only available with the six (although we’re not sure anyone desires the Tribeca).

For 2011, only the Forester gets Subaru’s third-generation flat-four. Known as the FB, the new engine looks pretty similar to its predecessor at first glance: 2.5 liters, 170 hp. While the displacement of both the EJ25 and the FB25 round to 2.5 liters, the FB is slightly larger, at 2498 cc versus 2457. This bump in size accounts for the 4 lb-ft increase in torque, to 174.

Subaru says the main motivation for the new engine was improved efficiency, something for which its engines have never been torchbearers—especially when they’re controlled by the right feet in our office. Compared to last year’s car, the 2011 Forester 2.5X gets an extra mpg in the city as rated by the EPA, at 21, while highway consumption is rated at 27 mpg. (Those figures apply to both the manual and the automatic; last year’s Forester carried ratings of 20/27 with the stick and 20/26 with the slushbox.) A 1-mpg improvement in city efficiency may not seem like much, but with the transmission and drivetrain staying the same, five percent is a fairly substantial gain. Subaru claims a 28-percent reduction in friction losses within the engine, with the biggest contributors being lighter pistons and connecting rods, as well as a drop in piston-ring tension. The less the engine has to work to keep spinning, the more efficient it can be.

New Heads on the (New) Block
Despite all the similarity to its predecessor’s specifications, the FB is all-new, including the block and the heads. The biggest fundamental difference between old and new is that the FB’s camshafts are chain driven, with all variations of the engine now carrying twin cams in each head. Going to chain-driven cams allows the valves to be placed at a narrower angle to each other. This let the engine designers shrink the bore, from 99.5 mm to 94. The smaller-diameter cylinder and increased stroke (now 90 mm, up 11) lets the FB suck air in more quickly, and the elongated cylinder also results in less unburned fuel during cold starts. Both intake and exhaust cams are equipped with variable valve timing.

Even though the stroke is slightly longer, the FB’s exterior dimensions are basically unchanged from the EJ’s. Subaru achieved this by employing asymmetrical connecting rods like those it used to increase the stroke of the flat-six in the Tribeca without drastically changing the engine. The lamb-chop-shaped rods also ease assembly of the bottom end. Subaru says 80 percent of the engine’s cooling capacity is routed to the head, and it even added a cooling circuit to the exhaust-gas recirculation channel. By doing this, it was able to reduce NOx emissions.

The intake manifold is plastic, like the outgoing EJ’s (save the cast-aluminum unit on the STI), but this new manifold incorporates four tumble-generation valves, one just upstream of each port. They look like half of a throttle valve and, through electronic control, manipulate the intake flow to maximize efficiency.

More Payoffs Imminent
Doing a complete overhaul of an engine for a one-mpg boost in fuel economy might seem like a waste, but Subaru has its reasons. Performing these same upgrades to the EJ would have resulted in a much heavier engine; as it is, the FB is only marginally heavier than the old mill. We were surprised that the FB doesn’t have direct injection, but Subaru tells us it will add the technology soon. The company says that next-generation transmissions—the Forester’s auto is an old four-speed—more-efficient engine peripherals, and an optimized driveline in conjunction with the FB would (read: will) also enable substantial increases in efficiency.

Expect to see a 148-hp, 2.0-liter version of the FB—dubbed FB20—in the new Impreza when it lands in showrooms this fall. That engine will feature the same stroke as the 2.5-liter, but with a slightly smaller 84-mm bore. The car should bear a strong resemblance to the Impreza concept Subaru showed at the Los Angeles auto show this past year. Subaru won’t comment on transmission options, but a smart bet would put money on a six-speed manual as standard, with the optional four-speed automatic replaced by a CVT. The latter should get close to—if not achieve—40 mpg on the highway.

Another car the FB20 likely will power is the Toyota/Subaru rear-drive coupe that Toyota showed as the FT-86 concept. We expect that a blown FB will power the new WRX, and our fingers are crossed for a turbo edition of at least Subaru’s version of the coupe. Either way, greater efficiency and a looming hot-rod or two will keep Subaru showrooms busy. Didn’t you hear? Subaru sold 263,820 cars in the U.S. last year. That’s a record number for Subaru—a tremendous 21.8-percent increase from 2009—and a lot of flat-fours.
Bob
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Old 02-01-2011, 10:06 AM   #2
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I understand that the FB is laying down the foundation for future changes that will result in more power and better mpg, but so far, I'm not impressed. There is nothing in this article that would make me want to trade in my EJ Forester (if I had one) for an FB Forester. Nothing that would make me rush in to buy a Subaru if I were on the fence.
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Old 02-01-2011, 10:36 AM   #3
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Originally Posted by max_stirling View Post
I understand that the FB is laying down the foundation for future changes that will result in more power and better mpg, but so far, I'm not impressed. There is nothing in this article that would make me want to trade in my EJ Forester (if I had one) for an FB Forester. Nothing that would make me rush in to buy a Subaru if I were on the fence.
The thing is 90% of car buyers will not have a clue what is different, all they will know is that the engine is new and gets better fuel mileage.
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Old 02-01-2011, 10:38 AM   #4
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I'm pretty impressed at the 40 mpg estimate on the highway. You don't see many AWD's achieving that number.
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Old 02-01-2011, 10:44 AM   #5
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What is more interesting is the direction they are taking with their motors. More and more are becoming chain driven and a change in head design could allow for more room for the DI nozzle in the future.

Tony
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Old 02-01-2011, 11:40 AM   #6
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Interesting stuff, but not a whole lot that we didn't already know here. Probably to be expected.

I still think the FB25 in the Forester this year is a teething year, to iron out the bits. Which is a good plan, and helps ease the idea of "not buying the first year of new technology" theory, for fear of unforseen complications.

The 2012 new Impreza is going to be the showcase for this engine, and it wouldn't surprise me one bit if the engine all of the sudden got a whole new set of output stats, just waiting in the ECU's wings...

It would be slick if the new sporty impreza based on the Impreza Design Concept had an option for a 200hp FB25 with a 6-speed manual gearbox, or an automated clutch gearbox behind it, with symmetrical or VTD AWD.

That would be something for the later WRX/STI turbo models to build on, once they get ported over.

Although I still would go even a step further and wish for an EZ engine in there... even an EZ32 down-sized version of the EZ36, if they would want to keep the big displacement for the Outback, Legacy, and Tribeca.

Last edited by HipToBeSquare; 02-01-2011 at 11:45 AM.
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Old 02-01-2011, 11:52 AM   #7
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Yeah I'd rather have them release the engine slowly, in its least complicated form, so they can work out the bugs.
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Old 02-01-2011, 12:26 PM   #8
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Quote:
Originally Posted by Turn in Concepts View Post
What is more interesting is the direction they are taking with their motors. More and more are becoming chain driven and a change in head design could allow for more room for the DI nozzle in the future.

Tony
yep, and they say it in the article too.

Quote:
We were surprised that the FB doesn’t have direct injection, but Subaru tells us it will add the technology soon.
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Old 02-01-2011, 01:06 PM   #9
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Well if the 2012 impreza is going to get a smaller engine as an entry point, no reason not to bump the power up on the 2.5. ~150hp for the 2.0 and ~200hp for the 2.5? I think that would be great.
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Old 02-01-2011, 01:40 PM   #10
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Quote:
Originally Posted by Honns View Post
I'm pretty impressed at the 40 mpg estimate on the highway. You don't see many AWD's achieving that number.
That's a random guess about a future model, not a real number.
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Old 02-01-2011, 01:42 PM   #11
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Up to 35 mpg is the number I've seen elsewhere. And that's impressive for a nice, compact (not sub-compact), AWD, non-hybrid vehicle.
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Old 02-01-2011, 02:11 PM   #12
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With a complete engine redesign, I could understand keeping power output the same in the name of higher efficiency, but 1 mpg just doesn't seem very impressive at all (even considering the lack of DI). Hopefully DI will make up for it with some impressive efficiency figures. Also, I hope they are able to squeeze slightly more oomph out of it in the FT86.
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Old 02-01-2011, 02:52 PM   #13
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"Subaru - Will Believe It When I see It"
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Old 02-01-2011, 04:53 PM   #14
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If some of the comparison pictures were to scale, it looks like the crank pins (conrod big ends) have reduced in diameter for the FB.

1lb weight gain is disappointing also.
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Old 02-01-2011, 06:00 PM   #15
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Quote:
Originally Posted by max_stirling View Post
I understand that the FB is laying down the foundation for future changes that will result in more power and better mpg, but so far, I'm not impressed. There is nothing in this article that would make me want to trade in my EJ Forester (if I had one) for an FB Forester. Nothing that would make me rush in to buy a Subaru if I were on the fence.
The new engine "feels" peppier than the previous one. It definitely feels stronger in the lower RPM range. It's especially apparent with the 4EAT. I suspect that the difference would be harder to notice with the 5M/T. Does that justify trading in a 2006~2010 Forester for a 2011 Forester? Most likely not.
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Old 02-01-2011, 06:06 PM   #16
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The article says that both intake and exhaust cams are equipped with VVT. I wonder if that's true/verified. Someone here (with access to the engine innards) was saying that VVT was only on the intake.
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Old 02-01-2011, 06:43 PM   #17
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Quote:
Originally Posted by neg_matnik View Post
The article says that both intake and exhaust cams are equipped with VVT. I wonder if that's true/verified. Someone here (with access to the engine innards) was saying that VVT was only on the intake.
It probably depends on the version of the motor. There will certainly be different packaging and details depending on the vehicle.
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Old 02-01-2011, 06:53 PM   #18
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needs DI..
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Old 02-01-2011, 07:39 PM   #19
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Originally Posted by amdmaxx View Post
needs DI..
Only if they are sure it won't coke up. DFI engines with dry intake tracts have exibited carbon coking problems without the solvent effects of gasoline in that area.

If that problem is solved for sure... bring on the DFI. If not, port fuel injection still works.
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Old 02-01-2011, 08:04 PM   #20
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Originally Posted by arghx7 View Post
Yeah I'd rather have them release the engine slowly, in its least complicated form, so they can work out the bugs.
Its been out for ~6 months or so in the Forester.
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Old 02-01-2011, 08:40 PM   #21
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Quote:
Originally Posted by HipToBeSquare View Post
Only if they are sure it won't coke up. DFI engines with dry intake tracts have exibited carbon coking problems without the solvent effects of gasoline in that area.

If that problem is solved for sure... bring on the DFI. If not, port fuel injection still works.
That's easy to fix... just eliminate the EGR system.
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Old 02-01-2011, 08:51 PM   #22
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Its been out for ~6 months or so in the Forester.
I would bet more on a two to three year cycle that will include direct injection and some retuning and possible cam tweaking by the end. All of the other subie engines lately (last 20 years) have had a bump in power within two to three years. I am betting the main thing Subaru is working on is getting all the manufacturing up to speed. One thing to consider about the power level is that subaru does not want the NA forester competing with the turbo one. If they bumped the power up 190 to 195 the NA version is getting pretty close to the 224 the turbo modles making. Would most buyers pass on the turbo for the cheaper NA version?
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Old 02-01-2011, 09:20 PM   #23
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I still think the FB25 in the Forester this year is a teething year, to iron out the bits. Which is a good plan, and helps ease the idea of "not buying the first year of new technology" theory, for fear of unforseen complications.
agreed. this is just like when the ej25 first came out in 96. at first it only made 155hp and required premium. 1 year later, it made more at 165hp and used regular fuel.
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Old 02-01-2011, 09:36 PM   #24
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Yeah, i'd definitely wait until the kinks are worked out. You just never know what kind of problems they haven't ironed out. I should've done that with my BMW.
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Old 02-02-2011, 09:53 AM   #25
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I bought a 2011 Forester with the FB engine, traded in our '07 FXT. I like everything about the new Forester better except the fact that they both have the same 4EAT tranny. It's too bad they didn't match the 5EAT out of the '05-'09 Legacy/Outback's with the FB engine as I am not feeling the CVT's.

As far as the engine, no problems, no "kinks"...it's great.
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