have not yet checked pinion angle, and no last time i raced was with a 3" cutout beneath the passenger side door, glasspack was not installed. So glasspacks dont flow good? Reason for installing was to reduce noice because of my ory. My glasspack looked exactly like this one http://images.google.com/imgres?imgu...%3D18%26um%3D1

 

i always race with cutout open and its good for 2 tenths and 2mph

 

Glasspacks are notorious for having horrible flow depending on the design. \

The Borla XR1 flows about 850CFM for oval and 1400 for Round (from what i've read) while a 3" Louvered glasspack is probably more like 300cfm.
I use a Dynomax Bullet as a resonator which is a Perforated core and I'm seeing flow ratings from 500-1000cfm on perforated cores.

I've seen several posts on this site talking about having your pinion angle out of whack after a drop. This prevents the suspension from allowing proper weight transfer.