New Custom Exhaust Installed - Review

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" – 3.5" 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.

(410) 540-9990

www.benchmadeproper.com

I will post up some video later.

Looks outstanding. Thank you for posting all of this information. So basically the installer did not have to touch any of the urea/ad blue piping, tank etc. right? The DEF is still in place too?

This thread was easier to read versus E90post... thanks for posting. I wonder if we can get some colored tips too - would like to add some black ones to match the trim and keep the soot hidden.

@cssnms, I spoke to Joe and was very informative, he's waiting on your DYNO runs and the car to start production. He as well as I hope that this mods brings in some gains, cause as I stated to him it is worthless if no gains are available from a product. he told me the estimated price tag. Give me call 787-459-4518 and Ill tell you ok

@ EYE4SPEED, I gather Joe is up for suggestions . I like the fact tahta black tips can be available

Looks good. I'm not a huge fan of the single wall tips but to each their own. Let's see/hear some videos!

It's funny just to look at some of the differences from Euro exhaust to US.

Euro center section:


US center section:


Euro DPF:


US DPF:

Originally Posted by julesandtrish

Looks outstanding. Thank you for posting all of this information. So basically the installer did not have to touch any of the urea/ad blue piping, tank etc. right? The DEF is still in place too?

You all are welcome - anything to advance the cause!

As to your question regarding the DPF/DEF, correct, that was my choice. I did not want to risk it throwing codes or going into limp mode, so I didn't touch the cats, NO2 sensors, DEF or DPF. This is simply a cat-back system.

Installation is quite simple and only requires the two pipes to be cut after the Y pipe and 2 flanges (which will be included) to be welded on, then it's as simple as attaching the exhaust. Any exhaust shop can do this.

Originally Posted by EYE4SPEED

This thread was easier to read versus E90post... thanks for posting. I wonder if we can get some colored tips too - would like to add some black ones to match the trim and keep the soot hidden.

Benchmade will install any tip you want. If you look at their gallery on their website you can see they offer blue, black, quad, double wall or whatever. I like the single wall because it gives the illusion the tip is larger. It's actually a 3" tip same as stock, but the opening is 3" vs stock which closer to 2 3/4".

Originally Posted by Axel61

@cssnms, I spoke to Joe and was very informative, he's waiting on your DYNO runs and the car to start production. He as well as I hope that this mods brings in some gains, cause as I stated to him it is worthless if no gains are available from a product. he told me the estimated price tag. Give me call 787-459-4518 and Ill tell you ok

Yea I told him in the next couple of weeks for gains. Even if gains are non existent (which given the improved airflow I can't see how that could be the case), I don't believe it to be a waste. The weight savings alone is HUGE, not to mention with the improved flow the hot exhaust gases can more quickly exit which I suspect will help to reduce EGT's (high egt's are bad for diesels).

Originally Posted by hotrod2448

Looks good. I'm not a huge fan of the single wall tips but to each their own. Let's see/hear some videos!

It's funny just to look at some of the differences from Euro exhaust to US.

Euro center section:

Thanks. Benchmade will do ANY tip you want, that's what's nice about it. If I get sick of the single wall tip they can easily be removed/replaced. I like the single wall because of the larger diameter outlet, not to mention it looks more custom.

How long did the complete install take? I know you were the first and had to wait longer, but did the installer say how long it would normally take?

Originally Posted by julesandtrish

How long did the complete install take? I know you were the first and had to wait longer, but did the installer say how long it would normally take?

2.5 days. These guys are experienced exhaust fabricators, so they know what they are doing and are very efficient. Considering I was not messing/experimenting with the DPF, cats etc, it was a pretty straight forward job and not much different than a gasoline car. I imagine the turnaround time for them to fabricate an exhaust and ship out would be similar.

Originally Posted by cssnms

2.5 days. These guys are experienced exhaust fabricators, so they know what they are doing and are very efficient. Considering I was not messing/experimenting with the DPF, cats etc, it was a pretty straight forward job and not much different than a gasoline car. I imagine the turnaround time for them to fabricate an exhaust and ship out would be similar.

Excellent. Thanks. Can't wait to see/hear the video.

Nice, looks good. I was just under my D the other day and I was looking at doing something similar as long as I'm still under warranty. It shouldn't take an experienced welder more then a couple hours to fab this up given he has the material.

btw two 2 1/2 pipes are not equivalent to a single 6"...

And get some videos up!!!

Originally Posted by Concentric190

Nice, looks good. I was just under my D the other day and I was looking at doing something similar as long as I'm still under warranty. It shouldn't take an experienced welder more then a couple hours to fab this up given he has the material.

btw two 2 1/2 pipes are not equivalent to a single 6"...

And get some videos up!!!

Like I said, I wasn't sure if I was remembering correctly. Please post up the conversion table if you have it handy. I will look for it in the mean time.

area = pi*r^2
area of two 2.5" pipes = 2*(pi*1.25^2)
=9.82"^2
area of two 2.25" pipes = 2*(pi*1.125^2)
=7.95"^2
area of one 3" pipe = pi*1.5^2
= 7.07"^2

I was a little off. It's more than 3" and less than 6".

I believe the man said (2) 2.5" pipes was equivalent to a 6" pipe. All of the above math was right except for the last equation.
It should read A=pi*3^2= 28.26 in^2. This is massively different than 9.82in^2. Not sure why the comparison was made to a 6" diameter pipe though. Perhaps he meant to compare to a single 3" diameter pipe like the math above showed :-)

A quick way to do this is to square the diameter and keep the sum of the squares equal.

i.e. 6" pipe: 6 squared = 36

3" pipe: 3 squared = 9

Therefore it would take roughly 4 (four) 3" pipes to equal the area of one 6" pipe.

This approach is not exact, but is a close enough approximation.

I'm a chemical engineer, and have done many piping pressure drop calculations. When you are in a meeting and someone asks - what happens if I change this 6" pipe to 3", you can relatively quickly tell them how many pipes they would need to keep the pressure drop the same.

Originally Posted by AZ335D

A quick way to do this is to square the diameter and keep the sum of the squares equal.

i.e. 6" pipe: 6 squared = 36

3" pipe: 3 squared = 9

Therefore it would take roughly 4 (four) 3" pipes to equal the area of one 6" pipe.

This approach is not exact, but is a close enough approximation.

I'm a chemical engineer, and have done many piping pressure drop calculations. When you are in a meeting and someone asks - what happens if I change this 6" pipe to 3", you can relatively quickly tell them how many pipes they would need to keep the pressure drop the same.

Less the very slight non-scalability of the boundary layer friction at the pipe wall, that approximation is pretty darn good for diameters that are well inside an order of magnitude different.

Enough science, we need video!

That's a neat exhaust upgrade. Here in Texas, we do not get an emissions check on diesel vehicles. My inspection only costs $14.95 for the basic safety inspection. This is causing me to consider going to a more simple setup if i were to upgrade. I'm wondering if the catalytic convertor could be eliminated from the system and put the y pipe further up stream. I don't know where sensors are put in the system so i wouldn't remove anything that the ECU (or whatever system) looks at. I have also read of people removing the DPF but this sounds like it could cause trouble. It would seem to me that the urea system and its associated sensors will need to be left as is. One more question. What website did the guy get the exploded view of the US and European exhaust setups?
thanks, Mark

Originally Posted by BB_cuda

One more question. What website did the guy get the exploded view of the US and European exhaust setups?
thanks, Mark

RealOEM

Originally Posted by BB_cuda

That's a neat exhaust upgrade. Here in Texas, we do not get an emissions check on diesel vehicles. My inspection only costs $14.95 for the basic safety inspection. This is causing me to consider going to a more simple setup if i were to upgrade. I'm wondering if the catalytic convertor could be eliminated from the system and put the y pipe further up stream. I don't know where sensors are put in the system so i wouldn't remove anything that the ECU (or whatever system) looks at. I have also read of people removing the DPF but this sounds like it could cause trouble. It would seem to me that the urea system and its associated sensors will need to be left as is. One more question. What website did the guy get the exploded view of the US and European exhaust setups?
thanks, Mark

Eliminating the cat will more than likely cause problems for the urea injection system. There is a n02 sensor just after the car. Removing the cat will likey increase the n02 output which would then trigger the def to inject more urea and or possibly throw codes. i thought about this long and hard and it wasn't a risk i was willing to take at least until someone can demonstrate they can reprogram the ecu/def. the dpf can be deleted and the ecu reflashed to accomodate for this. there is a company in europe offering this service for u.s. cars and i believe there is a u.s. company on the west coast now offering this service. not sure if one can delete/remove the dpf without addressing the def system though.

so Chris...do you have a vid you can post?

Originally Posted by Capt_Amazing

so Chris...do you have a vid you can post?

Sorry, I have not posted yet. I promise I will get it done this weekend. I still need to do the follow-up dyno too. Yea I am slaking...