So one of my customers owns a 919 and brought it to the shop this morning for a dyno run. He fabricated his exhaust by cutting and rewelding the single portion of the head pipe that runs to the y-pipe. turned it out and cut a scorpion can in half. Just to make everything clear he is running a 15 tooth front sprocket and premium fuel. No power commander.
His dyno numbers came out to 99.08 hp - 61.79 lbs torque and afr of 13. The afr and torque curve was flat all the way across the chart.
I thought that was pretty good numbers for a cheap exhaust mod.
The stock numbers I supplied are from a dyno run on my bike a while back. It is completely stock. According to Honda the hp at the crank is 107. Taking into consideration an approximate 10% loss in hp from the crank to the rear wheel then 96 rwhp would be about right.
I'm no engineer but I'd say a 3 hp gain at the rear wheel is pretty good for a simple exhaust mod.
Maybe Lord Duckhunter is lurking around somewhere and can weigh in on this matter.