Hi Rick
If you are using Mummerts ram horns check the outlet diam. I'm setting up a temporary exhaust for a test bed and assumed the outlet diam. to be 2" (I know measure 3...4....5 times
cut/ spend money once) so it came as a surprise to find 2" pipe falls right in. The outlet is nearer 2-1/8". So 2-1/4" would give a nice step of 1/16" in the right direction but check bolt clearance as the bolt fixing centres is 3". I had to make my own flanges as I could not find any 2 bolt on 3" centres.
good luck with the project
stuey