Your 18 years of experience (or is it 18 years old) Porsche Master Mechanic is wrong. The O2 sensors are on the header cats (1st set) like bmwm750 stated. No way for a CEL to come on.
This is absolutely false. I took the secondary cats off over a year ago and have driven thousands of miles on and off the track. No CEL. This really isn't something to do to gain HP as you will never notice the difference but it will alter the tonal quality of the exhaust which can be just as rewarding as a few HP.
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2000 Black Boxster S
EVO Intake & GIAC Tuning
Headers & Porsche Sport Exhaust System
ROW M030 Suspension
Front & Rear Strut Braces
B&M Short Shift & EVO Billet Linkage
MOST of the counties in PA have emmissions. With the exception of a few, however, they're visual only. So a lot of cars like these can get away with "Yep, there are still cats on it!" as long as the mechanic doesn't know it's supposed to have two