im wondering when the 2nd turbo comes on should the car spike or have less than 10 psi at transition if the cat is clogged for sure?

 

If the cat is clogged, you'd likely get less boost and power. Turbos don't like restrictions.

Dale

 

IIRC, boost spikes at transition happen because the turbos are spooling more quickly, usually due to an opened up exhaust (DP+catback or better).

A clogged cat would cause a reduction in boost best seen as a reduction in boost in the upper RPM range.

-bill