The lamb-chop-shaped rods also ease assembly of the bottom end. 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. Both intake and exhaust cams are equipped with variable valve timing.Įven though the stroke is slightly longer, the FB’s exterior dimensions are basically unchanged from the EJ’s. 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. This let the engine designers shrink the bore, from 99.5 mm to 94. Going to chain-driven cams allows the valves to be placed at a narrower angle to each other. 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. The less the engine has to work to keep spinning, the more efficient it can be.ĭespite all the similarity to its predecessor’s specifications, the FB is all-new, including the block and the heads. 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. (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. 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. 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. This bump in size accounts for the 4 lb-ft increase in torque, to 174. 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. Known as the FB, the new engine looks pretty similar to its predecessor at first glance: 2.5 liters, 170 hp. 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).įor 2011, only the Forester gets Subaru’s third-generation flat-four. Lowlier Subie models have a SOHC EJ of identical displacement that makes 170 horses. 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. The EJ-series flat-four has ruled the Subaru universe since it debuted in the 1989 Legacy.
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