fourwhls

I am to the point in my build where I really need to start ordering parts to build the exhaust. I am still not sure which direction I want to go and would like your input.

The car is not street legal and will be used for both open track (road course) and autocross.

Car:
1992 Mazda Miata (2100 lbs)

Engine:
ASA spec LS1 out of a retired roundy round car (430/430 at the crank)

Headers:
Hooker block huggers
1-5/8 primary
2-1/2 collector

Constraints:
100db sound limit at some of the tracks I run (typically measured 50ft from full throttle section)
weight

My thoughts:
2.5 in off headers to X-pipe to a pair of mufflers then dumping toward the ground before the differential.

Questions:
1. X pipe or Y-pipe (obviously the y-pipe will be lighter). If Y, what size pipe after the Y?
2. muffler selection (smallest mufflers that will keep me within the sound constraint)
3. Lightweight car - In order to manage wheel spin, I'm looking for the options that will have the torque curve moving in more of a 45 degree angle on the dyno plot vs an instant 90deg step.s

I'm looking forward to your feedback.