Transversely mounted inline 6. Only Volvo have done it, to my (limited) knowledge. I bet the cylinder walls are razor thin and all the accessories/pulleys are special design for least possible thickness.
Volvo S80 2.9 specs
| Car type | 4-door saloon |
| Curb weight | 1649-1673 kg (3635-3688 lbs) |
| Introduced | 1999 |
| Origin country | Sweden |
| Gas mileage | 14.5-9.3 l/100 km (16-25 mpg US / 19-30 mpg UK) |
| CO2 emissions | 234 g/km |
| Views | 154 |
| Submitted by | Hoppelmoppel123 |
Performance
| 0 - 80 kph | 6.4 s |
| 0 - 100 kph | 9.0 s |
| 0 - 140 kph | 18.5 s |
| 0 - 160 kph | 21.9 s |
| 0 - 180 kph | 32.4 s |
| 1000 m | 29.8 s |
| 60 - 100 kph (4) | 10.8 s |
| 80 - 120 kph (5) | 15.1 s |
| Est. 100 - 140 kph | 9.3 s |
| Top speed | 235 kph (146 mph) |
| 18m slalom | 61.9 kph (38.5 mph) |
| 100 kph - 0 | 38 m (123 ft) |
Powertrain specs
| Engine type | Inline 6 |
| Displacement | 2.9 l (178 ci / 2922 cc) |
| Power | 200 ps (197 bhp / 147 kw) |
| Torque | 280 Nm (207 lb-ft) |
| Power / liter | 68 ps (68 hp) |
| Power / weight | 120 ps (119 bhp) / t |
| Torque / weight | 169 Nm (124 lb-ft) / t |
| Efficiency | 16 PS per l/100 km |
| Transmission | 4 speed automatic |
| Layout | front engine, front wheel drive |