what kind of sound reduction can i expect from racing beat presilencers with a single out exhaust, NA. which model is the most recommended with purely decibel reduction in mind?? what kind of performance upgrade could i expect over a normal flow cat?

currently have stock manifold, pre converters, aftermarket cat but is NOT high flow, and corksport cat back power series exhaust

 

Well.. The RB presilencer is normally a 2.5" [there's a REVTII model that's 3" and looks beefier].

It'll be quite a bit louder and better flowing than any cat. It's a 2.5" empty tube, surrounded by a larger tube with steel wool in between. Except the S4 version with a ~1CM tube in the middle to pickup back pressure.

I have a friend with RB Header-Presilencer to Apexi N1 and it's fairly loud and annoying [compared with my similar but with RB catback system].. But if you like it loud.. Alternatively, keep the stock manifold and get the precat eliminator pipe, and it should sound good - RB claims that this is their recommended setup for NA cars w/o carbs. [Though I have no idea why]