Trevor said for a standard motor 1 3/4 all the way will work best. For a motor with cams and other performance mods 1 3/4 out of the flanges for about 150ml then step up to 2. There is such a thing as too big apparently.
Ceramic coating claims to cut down radiant heat by 30%. Back pipe is about 80ml from my leg would be closer on earlier models with pegs further forward. Les said heat isn't a problem with his pipes.
I was led to believe the step in diameter had something to do with scavenging the hot gasses away from the head .. tis a mysterious black art that's for sure. They look the business Bruce.
All we can do is go with the blokes that have been doing it for a long time and trust what they have learnt. I like talking to these blokes the information, facts and figures just keep pouring out of them.
Whats wrong with the legs? I tried to get a swim suit model in ****star heels for the photo but there a bit thin on the ground at the local industrial estate.