Related: Automotive Powertrain
In 1999, Jorgen Svensson, the Volvo XC90's chief program engineer, went shopping for a V8. Volvo's first SUV was in early development and though it was slated to get both inline five- and six-cylinder engines, the automaker knew it would miss out on a lucrative slice of the American luxury SUV-buying demographic if it didn't offer V8 power. The problem was that Volvo had never made any V8s, and incurring the immense investment necessary to tool up for manufacturing a whole new engine was out of the question. So Svensson was tasked with looking for an off-the-shelf unit. At first he confined his search within Ford's operations, but Volvo's unwavering requirements for the amount of crush space between the engine and the passenger compartment dictated that the V8 had to be roughly the same depth as a compact V6. Ford didn't have anything that small, but executives pointed Svensson toward Yamaha, which had everything that Volvo lacked: expertise in building compact V8s, an existing manufacturing line, and spare capacity.
The result of the collaboration between Volvo and Yamaha is a study in how to squeeze a lot of engine in a little space. Measuring just 29.7 in. long and 25 in. wide, the XC90's V8 is compact, yet produces 311 hp @ 5,850 rpm and 325 lb.-ft. @ 3,900 rpm. "The packaging was the most demanding part of the project," says Svensson. He says the V8 had to fit entirely between the front frame rails in order to meet Volvo's front- and side-impact standards, and it had to be transverse-mounted to allow for enough crush space. On the most basic engine architecture level that meant that the angle between the cylinder banks had to be 60º instead of the standard 90º. They went further. To buy a few millimeters in width to accommodate the structural beam network, the left cylinder bank is offset half a cylinder ahead of the right bank. All accessory components (e.g., the alternator and A/C compressor) are bolted directly onto the engine itself without brackets. To save additional space, the exhaust camshafts are driven by secondary chains attached to the intake camshafts, and the starter motor is mounted directly above the transmission.
Shrinking the V8 came with a lot of headaches, which helps to explain why more automakers don't attempt to reduce the size of their engines even though under hood packaging space is at a premium. For example, a 60º configuration is prone to generate more vibration than a 90º unit, so Volvo had to add a counterbalance shaft to help tame the NVH. Also, while going bracketless saves space, it means the positions of accessory components have to be fixed very early in the design process, leaving designers little room to make adjustments later on. And generating over 300 hp in a very confined space produces a lot of heat, so Volvo has had to double-insulate the exhaust manifold and add heat shields.