Hi,

IMHO, there are a couple of other seemingly small considerations that make a big difference. First, the distance between the end of the exhaust and the front face of the bell-mouth is very important for cooling and for thrust optimization. I think there's some formula for that (ask Mr. Matt, Bob Wilcox or John Redman). Also, that 2 percent is a Big Deal! If you look up the pipe, you can see the offset in the exhaust cone (it's thicker on top than on the bottom). Straightening that out will make a big difference.