check this out .... http://www.installuniversity.com/in...on11.122001.htm

Each pair of catalytic converters restrict about eight ( rear wheel horsepower on stock LS1’s. David Vizard’s research shows that 2.2 cfm of flow at 20.4” of H2O will support 1 horsepower. 2.2 cfm is the optimum flow through the exhaust system and reflects open pipe flow. Assuming that the average LS1 puts 300 horse power to the ground, that is a 2.67% increase in power.


So for a stock LS1 that puts 300 to the ground and still has both cats but on a 2.5 inch y pipe.. An 8 rwhp increase happens when the cats are removed...

HP= Flow (cfm)/2.2 cfm 567.8 cfm/2.2 = 258.1 horses..
This means that the stock cats can support up to 258.1 horses...
("looks" like study was done in 1999)
So if i want two carsound cats they will flow 372/7 each x2= 755.4cfms

745.4/2.2 = 372.7 hp 2.5 inlet/outlet carsound cats can support..
I wonder if 28 inch H20 flow tests were for 3inch cats.. im not sure..
If thats the case then 2 3inch carsound cats can support 436 rwhp without losing any power at all...

Sounds good too me...