I got this formula from Frank Massey's AUTOiNFORM youtube videos. He said use: Brake HorsePower times .8 @ WOT. For example 2005 Saab 9-5 has 185hp at 5500 rpm. So 185 X .8 = 148 g/sec at WOT would be the minimum. I have only used it at few times but it seems ... Login to read more.