• Mar 7, 2007
So we were all ready to start going over the technical details of Subaru's new turbo diesel boxer, but after digging through the PR materials, we realized they gave us bupkis. No power figures, no displacement information, not even what models they intend to shove the new mill into. L-A-M-E. Regardless, what we do know is that the horizontally opposed engine won't need a balancer shaft and, of course, it will be attached to Subaru's symmetrical AWD system. Sales will be exclusive to Europe when it is released in 2008.

We'd encourage those among you with some technical knowledge to check out the gallery and maybe shed some light on the components of Subaru's new oil burner.


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  • 22 Comments
      • 7 Years Ago
      #18 To answer your queries:

      (a) & (b) Probably the same solution they use in all their other engines.
      • 7 Years Ago
      Hello. You've caught something there. Crude yes, primitive yes, perhaps even grotesque.
      • 7 Years Ago
      Dual overhead camshafts with roller-finger-followers on both banks, separate timing chains, VGT turbo with intercooler, common rail injectors. Not quite sure what the black coating on the piston shafts is, presumably a very hard layer to minimize wear. In a diesel, you have to forcibly cool the piston crown from below using an oil jet. Out at the liner, in a flat config the side of the piston that points skyward typically gets less oil while the other gets more. This may be especially true of an inline engine with forced cooling of the piston crowns.

      Interestingly, Subaru use a fairly small diameter, deep piston bowl with a pointy mound. This was state-of-the-art in European inline diesels 2-3 years ago, but the trend is now toward wider, shallower bowls because those are easier to cool. shallow bowls also give the fuel, which is injected at pressures of up to 200 atmospheres, more distance/time to mix with the fresh charge. This cuts down on PM formation, but then this engine features a DPF anyhow.

      Note how thin the counterweights on the crankshaft are - a key advantage of inline configurations. The reduced polar moment of inertia permits more rapid angular acceleration. The difference should be most noticeable in first gear. Thin counterweights also slice through the oil more easily, limiting oil foam formation and the associated oil aging.

      Since this is a diesel, there was no way around a main bearing on either side of each piston - though they are amazingly narrow. This increases the remaining free inertial moment of the second order, which is proportional to the distance between adjacent cylinders on the crankshaft. The only way to eliminate it without a compensation shaft is to have the inner two cylinders moving in the same direction, but that requires a much larger cylinder head for the outer two. Subaru decided to use symmetrical cylinder heads.

      What none of the pictures show is what is actually most critical in an flat config:

      (a) how does the design deal with sloshing oil in a tight turn? Dry sumps are an expensive option, one I suspect Subaru did not resort to.

      (b) how does it deal with gas pulsations between the front and rear cylinder groups? Forcing the air in the crankcase back and forth reduces available power and can set up standing waves in the oil carter.
      • 7 Years Ago
      The performance figures are probably sub-par.
      They would be lucky to get 150hp & 250ft-lbs even if they crank up the boost.

      Curiously absent is the picture of the exhaust manifold, hmmm.

      The pnuematic actuators at the top of the runner, does it only block the runner of one valve per cylinder [for swirl]

      That small gerotor oil pump driven by the exhaust cam looks neat. (straight to the turbocharger?)
      Nice vented rear brake rotors though, and the ever present L L R R.
      • 7 Years Ago
      Stout and nearly vibration free boxer design, four valve heads, common rail diesel, and sturdy looking rods... yup, plenty of modding potential! 8)

      I don't think it has variable valve timing, sadly, but the variable geometry turbo should make it nice and responsive.

      I'm willing to bet it'll make 200 hp at least. If it doesn't it won't be hard to make it produce that kind of power and more.
      • 7 Years Ago
      "2. Well, one big plus is that it uses a timing chain instead of a belt..."

      I agree. I have always thought that the use of timing belts added to much risk to engines as well as to much increased maintenance. The $400 tab for replacing a belt every 60,000 to 80,000 miles is lame. Say whatever you want about GM, but at least their engines all have chains which never need replacing. The only GM engine with a belt is the Daewoo engine in the Aveo and the Vue V-6, which is actually a Honda engine.
      • 7 Years Ago
      Odd about the Europe only thing. I had gotten word from my local Subaru sales rep that 08 would see Diesel Subaru's in America. Where's the Euro only info coming from?
      • 7 Years Ago
      I particularly like the hollow piston pins. By reducing the weight of the reciprocant parts, the engine may benefit of a quicker response and probably a higher redline compared to regular diesels, which added to the variable turbo geometry mentioned by #14, should make this engine a winner.

      I hope it works as good as we think it will.
      • 7 Years Ago
      Howard Kerr:

      "You do realize how ironic your statement about GM and timing belts is? Or maybe you don't?"

      While I realized that GM used to have many timing belts, I was not aware that they helped develop the concept. It is ironic. I am just glad to be rid of timing belts on my vehicles.
      • 7 Years Ago


      And if that doesn't work right, CAR SPECULATES that it will be a 2 liter engine producing 165 horsepower and 250 lb/ft of torque.
      • 7 Years Ago
      "Sales will be exclusive to Europe when it is released in 2008."

      Aarrgghh! Please bring it to the US, Subaru, I'm willing to buy one tomorrow.
      • 7 Years Ago
      #18 I had a look at the pictures some more and in answer to question (b), I reckon the main bearings create a semi-sealed section for each piston so there is no issue with standing waves being generated because there would be enough baffling between so counteract it. There would still be air movement around the crackcase but every engine has that.
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