Originally Posted by TheRacerBoss

I have had RPI on my 530i and I now have had custom Magnaflow (quad) for a couple of months
Let me tell you something you will never regret.

If you drive the car around with your family (wife and child) stay away from RPI.
My wife used to get so annoyed with that RPI note that she stopped driving with me in the bimmer. It has a BAD drone between 2200 and 2800 RPM. By drone I mean, there is a loud noise in the cabin which is super IRRITATING.

Now I have my custom quads using a Magnaflow 2 in 2 out muffler. It is AWESOME , it doesnt have that BAD drone and it is only a little less loud comparing the RPI. People in my car enjoy and love the exhaust since I was coming from an RPI. How much of HP gains or losses I have encountered is a different question but how much I enjoy my exhaust over the RPI, dont have words for it.

I have also heard and driven the RPI on the 550i. Its a load of fun both to drive and listen either Inside the cabin or outside the cabin. As for a 530i automatic, I would say, stay away.

On the other hand, if you have a manual 530 you might not mind the RPI so much.

Originally Posted by DarkKnight550

I have had it on my 550 since this past summer, and it does drone between 1500-2000rpms. Not too bad when flying solo, but when I have a full car and extra load on the engine it is very noticeable. When I emailed RPi about it they said this was normal and to drive in DS mode.

It does sound great and the gains and definitely proven, but If I were to do it over again I would go quad with a magnaflow custom setup. Apparently you can get that all done for sub $500; half of an RPi setup. However, the words still out on the gains, only one member had a before and after dyno. He did post some pretty good gains but with custom setups, every car is different.