Subaru's diesel boxer
by Damon Lavrinc on Sep 30th 2006 at 11:54AM 
The design of the horizontally-opposed engine has a myriad of benefits. One of the most common is its compact design, which allows the center of gravity to be lower in the host vehicle. Additionally, since the boxer's pistons cancel out much of the vibration, the rotational balance is second to none. Both of these advantages will lend themselves to the advent of the first boxer diesel, which will find a home within a variety of Subaru models in Europe and possible even here in the States.
Hiroyuki Ikeda, Subaru Europe's President, announced at the Paris Motor Show that the development of the H4 turbo-diesel boxer is almost complete. The design, pictured above, reveals two interesting tidbits: first, the turbo, which is traditionally housed towards the passenger side firewall on most Subarus, will be moved south of the crankshaft to retain the boxer's low center of gravity. Second, the new DOHC diesel will be outfitted with a timing chain, currently only seen on Subaru's H6 engines, and will be the first H4 so equipped.
If one of Subie's diesels does make it to this continent, expect it to reside under the hood of the new Forester.
[Source: GizMag via Straightline]
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Reader Comments (Page 1 of 3)
Jason 4:05AM (9/20/2008)
I've always liked Subaru vehicles; mostly because of their horizontally opposed engines and also because they're the only car manufacturer to mass-produce 4wd cars. Now that they're working on their first horizontally opposed diesel engine, I'd certainly hope to see it here in the USA. It's a fact that 4wd vehicles don't get the best fuel economy. Add that to the fact that the current engine doesn't put out very much torque, and you really need to have a diesel engine in the vehicle. It's LONG overdue. It puts out approx. 235lbs-ft of torque (after emission controls are added), with the awd vehicles like the Legacy, Outback and Forester, they should get around 25-35mpgs depending on what transmission options are chosen. My favourite would be a 5-speed manual shift transmission. I can't wait to see it here. All we can do is cross our fingers and pray.
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Davos 8:29PM (1/11/2009)
Where can I buy one of these Subaru Diesel Engines, I want one for my new boat? It is perfect fit for a tight engine bay. I would import from anywhere.
Is there anyone out there in Europe with a wreck or new engine available that will sell one?
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Tal D 1:03PM (9/30/2006)
It's about time we see more diesels for our automobiles; if we see this one. In my my unscientific opinion Subaru FWD is superior to others FWD I've owned..esp in snow.The engine's low center of gravity makes the difference.If they build this one as other good diesels are built with the endurance, longivity. and less fuel consumption but with the power and torque associated with diesels, this could be a very desirable means of transportation. Hopefully we will see it here and I thank Subaru in advance.
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Steve2 5:29PM (9/30/2006)
By passenger side for the turbo, do you mean port side or starboard side? Because the passenger side on a domestic Japanese car is the driver's side on a US version.
Lowering the CG for a Diesel will do a lot toward mitigating the increased weight.
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ruggels 1:08PM (9/30/2006)
i wasn't aware subaru still sold cars which were FWD in america?
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Jim in Tampa 1:09PM (9/30/2006)
I've driven a bunch of boxer engine cars including Subarus and I've never found them to be that smooth running.
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Tion 4:06PM (10/02/2006)
They don't. I have no idea what Tal D is taling about.
All Subarus are AWD all the time.
But this is exactly what the USA needs. Clean diesels in their SUV's and cars. A diesel would also go good with subarus AWD system. If subaru enginers it right, they could get upwards of 300lb torque from 2.5l. but a 2.0L 150hp 250lbtq would be ideal for all of subaru's model range. Not to mention the 40+ mpg a good diesel should get.
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james 1:59PM (9/30/2006)
I had been looking for a used Subaru Impreza or Outback 2.5 non-turbocharged years 2003 or newer. Every single one I test drove had problems with the engine. They never ran smooth or started easily and struggled to last this long. There is a piston slap problem with this engine that still hasn't been fixed. I can tell you right now Subarus are not made to last.
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MikeW 2:22PM (9/30/2006)
The boxing 4 has a second order moment imbalance, inherent to its configuration. (lookind down at the engine)
The large axial offset only exacerbates that imbalance.
Subaru's boxing engines have about a two inch axial offset, in order to fit the 5 bearing crankshaft and counterweights.(good for strength & boost, bad for balance)
The M5 axial offset is only 17mm.
and no constant pulsation exhaust manifold, to compensate for the L L R R firing [blub blub blub] of a boxing4.
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AK 2:37PM (9/30/2006)
#3, tell that to my Legacy which is pushed 194k without major problems. Now at 200K it starts right up. That's definitely a crap job they pulled there when putting it together.
Boxer engines feel different from your normal inlines so that may be why you felt that it didn't "run smooth." In any case I hope Subaru brings this engine over to the U.S. in their Legacy models. It would be great to have Subaru quality with superb fuel economy.
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Richard V 6:03AM (10/01/2006)
I have had 2 Subarus with over 100K with no engine problems. One was a turbo. I now have the 6 cylinder and like it a lot. Good low end torque with no turbo to worry about. I would buy another Subie again.
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AndyH 2:44PM (9/30/2006)
"2. i wasn't aware subaru still sold cars which were FWD in america?"
They don't, the entire Subaru lineup of vehicles sold in the U.S. has AWD standard. Not sure what #1 is talking about.
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chuck goolsbee 4:02PM (9/30/2006)
I've owned two "boxer" engined cars, a 1973 VW 1303 (aka "Super Beetle") and a 1989 VW Vanagon (aka "Waßerboxer"), I would have a hard time keeping a straight face while saying they were "smooth" or "rotationally balanced". That said, they were very sturdy and provided fine propulsion for their day.
If you are looking for a smooth engine, the inline six is the choice to make. Of course there always in the legendary I-12 (http://www.brit.ca/%7Etboicey/comics/inline12.html) but it is only ... um... legendary.
I've never seen nor heard of a horizontally opposed Diesel engine, but don't doubt that they have existed at one time or another. The American market is DESPERATE for alternative fuel options, and Diesel should be at the head of that pack. I run my VW TDI on vegetable oil and when I tell people that they are shocked. The idea of running a car for under a buck a gallon is worth the effort I put into it.
Big Oil can kiss my @$$ and keep eating those french fries folks!
--chuck
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Bob Zeliff 8:49PM (9/30/2006)
I'm very happy to hear that Subaru is working on a Diesel. If they make it as reliable as their H4 engines and it get 29-20% better fuel economy, we'll get one.
PS our family has had 8 subarus and something over 500 thousand miles with no major problems, so I have high expectations for the diesel.
bob
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sam 5:32PM (9/30/2006)
#3, your generalization is unfair. I've have a couple of legacys now over 200k, and subaru's 2.2L EJ22 is considered one of the most durable engines ever engineered. The 2.5L have had head gasket problems, which have since been resolved.
The problem that you're noticing is not with the engine, but with the owners. People who purchased Imprezza turbos beat the living snot out of their cars; i've yet to meet an owner who didn't drive one like a maniac.
The second hand market for those is like a killing field.
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risingsun 5:37PM (9/30/2006)
Subaru did make a small number of 90s Impreza 2.2s that were indeed just FWD. VERY rare.
And Subaru's boxer engines are TOUGH. I have two coworkers with original generation Outbacks with 250K+ miles, getting the same mileage today that they did brand new.
A 2007 Outback 2.5i basic wagon is a LOT of car for $21995. The interior is head and shoulders above almost anything for that kind of money. Versitile, capable, good mileage, and refined. The cabin is quiet, the materials are top notch. Panel fit is great, and the small details in the cabin are well thought out.
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Clarence 5:52PM (9/30/2006)
Subaru is going out on a limb on this one. If it does not run smoothly and reliably, this will harm the brand, perhaps, irreparably. They better get it right.
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Kumar 7:57PM (9/30/2006)
If they do bring it over here, we'd probably see it in all of the subaru line. I'm just hoping in the next 3 years, which will be just about the right time for my next ride. Anything before that would be too soon to work the kinks out. That's what our European friends / guinea pigs are for!
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Ian 4:25PM (9/29/2007)
I just want a Subaru diesel engine to put in my VW T25. And as one of your European 'friends' I'll be glad to -'iron out any problems' for you. Would you like your nose wiped as well?
Wasn't it a shame about the American motor industry! You made such.... well big ... cars. Ho hum....
Joshua 8:20PM (9/30/2006)
First off flat fours are NOT space efficient, an inline 4 of the same displacement occupies less space. The slightly lower c of g that you get with flat 4s could very easily be replicated with an inline 4 just by laying it on it's side. Something that would be very easy to do in a transversly mounted engine. The reason manufacturers don't is because it makes very little difference and introduces other packaging concerns... So what's the real reason that Subaru and Porsche use flat engines? Because if your commited to using a transversly mounted engine that must be on the wrong side of the driven axle, its the best way to cram as much of that engine as close as possible to that axle. This is important for Subaru otherwise they would be even more nose heavy than they are already, and it's important for Porsches (911s) otherwise they would be even more tail heavy than they are already. And that's it, that's the reason, please stop with the compactedness / good c of g garbage, thank you... Deep breath.
The important (and unspecified) issue about that diesel is wether they manage to make it out of aluminum or if they have to resort to a cast iron crank case. Because Subaru engines are entirely before the front axle an iron engine would make the car horribly nose heavy
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