As you can see in the photos below, the Reatta has a restriction in the stock exhaust manifold. Removing it should give more flow to the exhaust system. It can be ground out with a die grinder and carbide burr, but a hole saw works better. It is a very simple job. Should take no more than 15 minutes to do the job once you have the exhaust system apart to access the restriction.
Take a hole saw the same size as the inside diameter of the pipe and run it inside the pipe. You may remove a small portion of the thread for the O2 port but it is not enough to worry about. The exhaust is a low grade stainless steel so use plenty of cutting oil and slow speed.


Thanks to Padgett and Barney Eaton for use of these photos.
Thanks to members of the AACA Reatta forum for this information.