I have always used 15% for driveline loss then multiplied that number times the hp number and that gave me the hp loss/add either wheel to crank or crank to wheel. I was talking with someone yesterday and they said it didn't work that way. I said my car had 617 at the tire. I took 617x.15=92.55. 92.55+617=709.55 hp at the crank. Is this how this works? He was saying that they are 2 different numbers, but couldn't exactly tell me how. He is a Porsche 911 driver so maybe he just didn't like the comparison. For future reference and so I don't sound like an idiot, can you guesstimate crank HP by my math above?