This was definitely worth the $13 for an iphone app. In fact, it may be worth the cost of the iphone!
280 hp at the wheels using a weight guess of 3600 lbs. Assuming 15% for drive train losses, puts it at 327 hp at the crank. The S54 was rated at 333 hp. The 0 - 60 time was 6.7 sec with the traction control interfering off the start and through the middle of 1st and 2nd gear.