Catted Dp/Catless Dp with stock catback.

[sam0329]

Hey Guys,

I am planning to get a AR catted DP for my N54. I would like to find out how restrictive is the stock catback. I know there's a second cat inside the pipe. I want to keep the stock catback to keep the noise level down. But if that is the big factor to affect over all performance than I might get the Maddad catback as well. Any Logs to show the difference? Thanks.

[Blue55]

Call the guys at AR. They are very helpful and will give you info you want. They told me that their catless DPs flow significantly higher than the catted versions. I don't recall the numbers exactly.

I'm running stock DPs (the 1M has higher flow DPs than the 135) and Maddad mids. It's louder than stock and it sounds fantastic, but it is definitely not at all too loud for my taste. On the freeway the drone is gone and its barely louder than stock.

Harold at HP Autowerks is also a good source of info as he has done a lot of mods to the N54.

[135Pats]

The entire OEM exhaust system for the N54 1 sucks IMO, all three sections are quite restrictive, particularly the downpipes and midpipe (the midpipe is just garbage, no idea what BMW was doing with that). You won't see huge power gains from an aftermarket cat-back solution, but it will certainly rev more freely and you'll get decent weight savings. If you want to keep the noise down with aftermarket DPs, i'd combine them with Maddad/Berk midpipes and leave the OEM axle-back portion. That should sound pretty sweet. Hit up AR, they'll get you in the right direction.

[sam0329]

So Cobb sent me a PM and said Catless DP + after market catback will yield ~15HP over stock catback!