I've seen studies done on Mopar exhaust manifolds using an engine stand. There is no way a 1 7/8" outlet can flow as much as a 2 1/4" outlet...it's just physically impossible. If you "google" air flow through a pipe you'll find that if you increase the pipe diameter by 2 times your flow will increase by 4 times. So if you go from a 2" pipe to a 4" pipe your flow will increase by 4 times. There is a 21 percent increase in size if you go from 1 7/8" to 2 1/4" (actually 2.270-2.85" after machining). So if doubling the pipe size gets you 4 times the flow then increasing the size by 21 percent (roughly 1/5) you should get about a 20 percent increase in flow capacity.
If someone wants to double check me on these numbers please feel free. And yes I know that air pressure and friction play a role.
