The XFR-S packs a supercharged 5.0-litre V8 engine so it is most certainly not underpowered. We know that to Hennessey Performance that anything with stock power is underpowered so they now offer an upgrade for this machine called the HPE650. As you would have guessed, this pumps the power up to 650 horses at 6300 rpm which is a 100 hp hike over the stock car. This was achieved by modifying the air intake and the ECU was given a little tweak. This must be one drift-happy Jag!