Sorry for the delay had computer problems which required a total system restore and didn't correctly back-up photos and videos so I spent most of the weekend trying recover lost photos/videos.
First let me say that Joe and Brian at Benchmade Proper in Elkridge, MD did a phenomenal job fabricating this exhaust system for my 335d. It’s 100% stainless steel and tig welded throughout. They offer a lifetime guarantee which speaks volumes to the quality of their work. They were VERY accommodating and true professionals and I don’t say that lightly, since I can be a pain in the ass sometimes.
The exhaust looks absolutely fantastic from any angle, I couldn’t be happier. Since I was the first here in the US (that I’m aware of) to install a custom exhaust on a d, I wanted to get this right the first time, so I did a lot of research to help me in deciding pipe diameter and how they relate to exhaust gas flow rates (CFM’s), high flow mufflers vs. free flowing resonators etc. I had multiple goals in mind when I decided to take on this “experiment.” First, knowing that by their very nature a diesel engine’s exhaust note is usually much quieter than a gasoline engine even before mufflers and pipes are added. Therefore, I wanted to try and improve the sound quality of the 335d’s exhaust, since there was virtually no sound being emanated from the back of my car while at idle or when revved. Secondly, after closely examining the OEM exhaust we noticed how crushed many of the pipes bends were, not to mention some of the crazy angles BMW took to route the piping, which lead me to believe that exhaust flow could be dramatically improved, thereby reducing backpressure as well as reducing EGT’s just by intalling mandrel bent pipes. In addition, the mufflers were HUGE and I could barely feel any air flow coming from the tailpipe while at idle or when the engine was revved. So I suspected that the mufflers were not only heavy but also very restrictive. In a nut-shell I was looking to improve the exhaust note, reduce backpressure, egt’s and weight, and at the same time perhaps pick up a few extra ponies in the process.
That said, with some guidance from Joe at Benchmade I decided to go with 2.5” mandrel bent stainless steel piping connected to Vibrant free flowing resonators. Thought being unlike the i’s true dual pipe exhaust system (from headers back), the d has a single pipe coming off the header which then branches out to a split pipe system after the mid cat. The single pipe coming off the header which is oval in shape appeared to be approx 3.5” – 4” in diameter, which then narrows down to a approx 2.25” split pipe system, which is then crushed down to under 2” in diameter in some places. In theory two 2.25” diameter pipes coming off a single 4” pipe should provide adequate flow assuming of course the 2.25” OEM pipes’ had minimal bends and the diameter was consistent throughout the run – that wasn’t the case. Considering my car is tuned I decided to increase the pipe diameter by .25” and to maintain a consistent diameter throughout the run with minimal bends. Reason being two 2.5” pipes are equivalent to a 6”+ diameter single pipe (if memory serves me right), which is good for up to something like 500+ hp, so going any larger would not be accretive.
I decided on the high-flow resonators since they virtually offer NO restriction as opposed to a traditional muffler. I also thought that they would allow a bit more sound through then a traditional muffler since I suspected that getting sound from this system was going to be a challenge.
Well my suspicions proved right. While the exhaust note improved somewhat, more specifically there's actually some sound coming out of the tailpipes now and it is deeper in tone, the improvement I would consider marginal, so it was a little disappointing in that regard. Don’t get me wrong I am still happy that I am actually getting some sound now, but I was optimistic I was going to get a few more decibels. What we discovered going through this process is that the cats appear to be suppressing A LOT of the sound, as I imagine the DPF is as well. To give you an idea, when the twin OEM pipes/mufflers after the cat were removed and before the new system was installed, the car was started the exhaust note was still very quiet (will post some video of that too), not sure why BMW even installed such large/heavy mufflers – they actually look identical to the i’s.
That being said, I am very happy with the quality of the system/install, it simply looks fantastic! The system is also significantly lighter than OEM (+/- 25lbs). I also feel A LOT more air flow from the tailpipes at idle and when the engine is revved, which supports my belief that in addition to the DPF and cats, the rear pipes and mufflers were/are very restrictive. Before the install and aside from zero sound, I felt hardly any airflow from the tailpipes. I would like to believe now that I've been able to improve the airflow/reduce the back pressure that there would be some performance gains, not to mention perhaps some benefit in terms of reducing EGT's. It could be false perception, weather or whatever, but my car feels like it’s pulling harder. I plan to take the car back to the dyno later in the month.
While this was somewhat of an experiment for us US diesel owners I consider this a stepping stone of things to come for the US BMW diesel. While I am not brave enough (yet) to try removing the cats and to tinker around with coding for NO2 sensors, DEF system etc, perhaps another daring owner will be willing to advance the cause and take this process to the next level!
In summary I am happy with my decision and purchase.
Benchmade stated they would make this system available for purchase/shipped to anyone that is interested. You can custom tailor it if you like e.g. different resonator/muffler or straight through exhaust, bigger or smaller tips etc. Give Joe a call for pricing and information.
I will post up some video later.