It is also ideal when mated to Subaru’s standard symmetrical all-wheel drive system because of the engine’s compactness, light weight and ability to connect with the AWD transmission in a straight line.
Now, the new 1.5 litre ‘boxer’ engine has been designed to offer strong low to mid-range pulling power, known as torque, while also having the ability to rev to high speeds for brisk overtaking. So despite being the least powerful Subaru, the new Impreza 1.5R makes the most of its power and torque, providing comparable performance to most similar-engined lower-medium hatchbacks.
For example, top speed is 109 mph for the manual, with a 0-60 mph time of 13.7 seconds. Fuel economy is also respectable with 29.4 mpg on the Urban Cycle, 44.8 mpg on the Extra Urban Cycle and 37.7 mpg Combined – 2 mpg better than before. Exhaust emissions are also competitive at 176 g/km.
Power is now 107 PS (2 PS more) at 6,000 rpm and torque is 104.7 lb.ft at a low 3,200 rpm while the compression ratio is 10.1:1. However, the torque is greater at lower engine speeds than with the previous model, improving throttle response and flexibility.
As with all Impreza engines, the new 1.5 litre features twin overhead camshafts per cylinder bank (DOHC) plus an Active Valve Control System (AVCS) which is a form of variable valve timing. This enhances both low-speed pulling power and high-rev response.
Also shared is an electronic throttle for more responsive acceleration plus centrally-located spark plugs, pent-roof combustion chambers and multi-point fuel-injection with an ignition coil for each cylinder.
Of special interest is the 1.5 litre’s bore and stroke dimensions, selected to optimise combustion efficiency for low emissions and fuel consumption while providing strong power and torque.
In fact, the new 1.5 litre shares its 79 mm stroke with Subaru’s four-cylinder 2.5 litre turbo engine. Naturally, its bore dimension is a much narrower 77.7 mm.
Other efficiency measures include low-friction, lighter valve springs and a 4-2-1 equal length, ‘constant-pulsation’ exhaust system which avoids gas flow interference and speeds up the warm-up of the catalytic converter.
Ten-Speed Transmission/Symmetrical All-Wheel Drive
As with the new Impreza 2.0R and RX, the 1.5R has a five-speed manual gearbox with a low-ratio, dual-range transfer gearbox, effectively providing 10 speeds. Owners find this particularly useful when towing or covering difficult road surfaces as it provides extra engine-braking for greater control.
For the new model, the Impreza 1.5R has revised, slightly higher 2nd, 3rd, 4th and 5th ratios for improved high-speed refinement and enhanced fuel economy.
The symmetrical all-wheel drive system features a nominal 50/50 front to rear torque split. However, a centre viscous-coupling senses which axle has the best grip and varies this ratio in milliseconds according to the road surface.
This maximises tyre grip and handling accuracy, instilling confidence in the driver – especially on rain-soaked motorways or snowy country lanes.Published 23 August 2007