Thread: Bought Borla 2.25 In/Out Mufflers...Will they be restrictive?

Originally Posted by BillBoost37

2 x 2.25 = 4.5" of flow at the mufflers. You wont be restricted there. Now what you do from the Y forward..that's up to you.

not exactly

(pi*r^2)*2 gets you 7.94 sq inches of space (pi*1.125^2)*2

while 1 3" pipe(like your downpipe) has 7.06 sq inches

so it flows enough to outflow your downpipe but not as much as your simple math shows.

The biggest cat-back restriction is that the y pipe is more of a T pipe.