It’s mounted this way because the S80 could be had with either FWD or AWD, but to avoid the copious ammounts of torque-steer that a FWD V8 configuration would cause, this version was only offered with AWD. The engine itself is a 4.4L V8 designed by Yamaha, producing around 310 BHP. This oddity was only offered between 2006 and 2010.
Leave it to Volvo to mount a V8 transversally (Second generation Volvo S80)
