| Cars powered by 2.5-liter engines, like the Subaru | | | | The engine uses a timing belt that may have to be |
| Outback or Nissan Sentra, tend to be zippy and | | | | replaced every 100,000 miles (160,000 km) or so. |
| responsive, even though these two don't belong to the | | | | The Nissan Sentra engine, on the other hand, was |
| same class. | | | | introduced during 1982 with the Nissan Sunny, and has |
| The Subaru Outback engine has quite a history and | | | | gone through a series of incremental improvements. |
| evolution. Formally introduced at the 1994 New York | | | | By 2002, a new 165-horsepower SE-R was in |
| Auto Show, the car was launched initially with the | | | | circulation, coupled with a 5-speed manual transmission |
| DOHC 2.2-liter flat-4 engine, and was promptly given a | | | | or optional 4-speed automatic. |
| 10-hp improvement in 1998. | | | | The QR line of inline- or straight-4 piston engines from |
| A flat-4 design, also called a horizontally-opposed-4, | | | | Nissan come in displacements of 2.0 liters to 2.5 liters. |
| has two cylinders mounted on each side of the | | | | They share aluminum, dual overhead camshaft |
| crankcase. This is the same design used for the | | | | (DOHC) pedigrees with optional direct injection in |
| engine of the classic Volkswagen Beetle. | | | | four-valve configuration and variable valve timing. |
| The pistons move in opposite directions, analogous to | | | | The Nissan Sentra engine for the SE-R Spec V sport |
| a boxer slamming his gloves together, thus earning the | | | | compact variant is the 2.5-liter QR25DE, which was |
| nickname boxer engine. The counteracting motion | | | | originally mated to the Nissan Altima. It could put out |
| contributes to the substantial canceling out of vibration. | | | | 175 hp at 6000 rpm and 180 lb·ft (244 N·m) of |
| This is how the Subaru Outback engine evolved: | | | | torque at 4000 rpm, sufficient to accelerate the car to |
| * First generation - 2.2L SOHC 135 hp (101 kW) H4 | | | | 60 mph (about 100 kph) in less than seven seconds. |
| * Second generation - 2.5L SOHC 165 hp (123 kW) H4 | | | | The QR25DE comes out of the plant in Decherd, TN |
| * Third generation - 2.5L SOHC 175 hp (130 kW) H4 or | | | | with aluminum intake manifold, connecting rods made |
| 2.5L DOHC 250 hp (186 kW) H4 turbo | | | | of cast steel and vibration-reducing balance shafts. |
| * Fourth generation - 2.5i SOHC i-AVLS 170 hp (130 | | | | This 5th generations Nissan Sentra engine started |
| kW) H4 | | | | production in 2000, and has served its role quite well |
| The 2.5i models produce 170 hp and 170 lb-ft of torque, | | | | through the years, despite its share of mechanical |
| coupled to a six-speed manual transmission that | | | | glitches that have led to service bulletins and recall |
| enhances superb performance features. | | | | episodes. |
| Some owners of the 2.5-liter Outback engine have | | | | Some owners have observed comparatively higher oil |
| encountered head gasket problems or failures when | | | | consumption as well as valve screws in the intake |
| these overheat too often, resulting in thermally warped | | | | manifold becoming loose and leading to fluctuating idling |
| heads, but Subaru has already redesigned the head | | | | or loss of power. |
| gaskets with good success. | | | | |