I was curious as to why no one here is running a Borla exhaust on their E60? I have had very good experiences with them on past cars. Everyone is telling me to get an RPI but I am having a hard time pulling the trigger on a relatively new company over a very well established one such as Borla or Magnaflow. Opinions?

I've got borla, but it came on the car when I bought it so I can't compare it to stock. It has a nice subtle purr and isn't very overwhelming noise-wise. I don't think it has any performance enhancement...

I am your dream response! :P

I just sold my Borla and bought a used RPI (only 3 mos. used). Didn't notice if you a have a 6 or an 8 but I have an 8. When I bought the Borla, the RPI didn't exist. Borla does not make an axle-back system for the 545, not sure about other E60 models. So I purchased a universal Borla muffler and had a custom exhaust pipe created. This was much cheaper than buying an Eisenmann or Supersprint axle-back system. There were few, if any other choices for bolt-on axle-back systems for E60 545.

That being said, I was very happy with the Borla and it was a lot of fun to drive. I noticed no loss or gain of power, but it was never dyno'd so I don't have any objective data for you.

The difference with the RPI is quite noticeable.

First, the RPI will cost twice as much as a custom Borla system.

Second, the RPI is specifically designed for the car... not a universal muffler with a pipe. As others have noticed, the exhaust pipe attached to the RPI muffler is smaller in diameter than stock pipe, then expands to 3" where it attaches to existing stock pipe. I am not a physicist but my intuition tells me that this was done to maintain some back pressure, thus increasing HP without losing too much torque. I'm just guessing here! RPI has a good reputation here and they may not be willing to divulge all their engineering secrets. :)

Third, the sound is FANTASTIC! The Borla sounds MEAN..., the RPI sounds MEAN AND TUNED. The RPI sound is cleaner... more European, super-car sound. Borla is more raspy, American, muscle-car sound.

Fourth, there is a noticeable acceleration improvement with the RPI. Again, this a subjective assessment from the driver's seat. As I said before, with the Borla, I noticed no loss or gain. With the RPI, there is a noticeable gain.

Fifth, for $500 the Borla sounds good and is a lot of fun. Got lot's of compliments at redlights, parking lots, etc. If you are willing to pay $1000, the RPI is worth every dime and then some!

I have a shitty camera so the recordings aren't great, but here's a comparison on my car:

Borla:

RPI:

magnaflow is another option, but not as popular as the RPI. but yes it is cheaper, mostly we do magnaflow setups for those who want a custom quad setup, but also there has been a couple for just the dual as well. then again, there is no proven guaranteed power with magnaflow.