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2010 2011 BMW 5 Series Forum F10 F10 Technical Topics Engine, Transmission, Exhaust, Drivetrain, ECU Software Modifications F10 N55 Open ended J Pipes mod
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      03-20-2016, 02:46 AM   #1
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In my quest to get the right get sound for my N55, I thought an easy upgrade to a better exhaust note would be open the exhaust valve permanently. I found that in my N54 this is a great mod, but unfortunately on my non M Sport exhaust system I don't have a control valve. It's just annoyingly quite for a "sports sedan". Is that an oxymoron?

I started with a muffler delete and came back the next day to have straight throughs put on. At the time I was doing this mod so was FenixMike and he was reported that the resonator delete did absolutely nothing. I started going back and forth with him about choices and he suggested a straight through so that's what I tried. I ended up with magna flows 14" and it was a great tip. It sounded much better, but my 6 cylinder had that Honda sound and it wasn't for me. I'm sure it's much better on an 8. Plus, I couldn't handle the drone anymore. I looked at how other people addressed this issue with aftermarket exhaust systems in different cars and that's when I discovered the Helmholtz resonator equation.

QOUTE:

"You can use a listening app (frequency analyzer). It is usually between 1400-2000 rpm cruising in 6th gear when afm is not engaged. The hz value varies but it is usually from 90-120hz. Mine was about 110hz and could rattle change in my cupholders.

Simply put, the formula for determining the length of a Helmholtz chamber used to knock out a drone frequency is:

1100 feet/second (roughly the speed of sound) divided by the target frequency you're trying to eliminate (in cycles/second) gives a full wavelength in feet per cycle. Divide this number by 4 to get a quarter wavelength (a much more convenient length to work with). Finally, multiply this wavelength by 12 to get the chamber length in inches.

So with my 110hz value it looks like this ( 1100 / 110hz ) / 4 ) x 12 = 30 inches

So the length of the helmholtz chamber needed for killing 110hz drone is 30"."

UNQUOTE

Source: http://flg8cc.com/vb4/showthread.php...nd-application

App used in iOS:
iAnalyzer Lite by Phyar Studio
https://appsto.re/us/SBxAu.i

I had custom 2" j pipes made and that eliminated the drone completely. It was low bass sounding from 500-2500rpm, 2500-2900rpm quite, and from 3k and up the exhaust note would start to come into the cabin. I thought that was perfect, until I got bored again. I thought what if I could get the best of all worlds, straight through which has a very tuned exhaust note, the muffler delete gurgle and maintain no drone by cutting the tips of the J pipe open. I did and holy shit it worked, almost. About 20-30% of the exhaust went out the open pipe and the rest through the straight through. At freeway speeds there is still noise cancelation where very little of the exhaust goes through the open j pipe. When I go WOT it gets very loud at any speed which is desired.

I'm very pleased with the results. It gives my 5 series a very adult/sport sound without pretending to be an exotic race car. It has nice grunt on launch and a deep note that doesn't sound like there's a leak or hole in my exhaust. Freeway speeds drone is 90% eliminated and loud when I want it on WOT. Now I wonder if I had a delete with an open ended 2" Helmholtz resonator. Would that be as loud as a delete, and reduce freeway drone by a large percentage? Hmmmm, still debating that one, but for now I'm happy with the end result. DP is coming back for a stage 2 tune so I'll report back to see how that affects the open j pipes.

The delete was 100 - installed
Straight throughs 150 - installed
J pipes 50 - installed
J Pipes opened with turn downs 40 - installed

If I didn't experiment would have been about 190-200. For a budget exhaust this is the way to go. Open ended 2" J Pipes on straight throughs.

Here is a video that will kinda give you an idea. It's much better in person. I'll get someone to help record so I can do some drive-bys.



Cold Start:
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      03-20-2016, 08:00 AM   #2
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that's AWESOME bro! why was it your calves were the whitest things on the whole video screen? and for a second i thought you were gonna do your own rendition of "Fast n Furious" by launching off the parking lot garage anywho, the exhaust note actually sounds pretty damn good! and you thought of all this?? maybe patent this and market it ASAP! How are you able to determine how much exhaust is actually going out the open pipe...and is your undercarriage eventually gonna build up any carbon underneath?
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Last edited by lsturbointeg; 03-20-2016 at 08:07 AM..
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      03-20-2016, 08:24 AM   #3
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Very cool indeed! Sounds awesome.

How about the old beater station wagon with the flat in the picture? Looks like that old family truckster has seen better days.

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      03-20-2016, 09:47 AM   #4
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Quote:
Originally Posted by Jcbama85 View Post
Very cool indeed! Sounds awesome.

How about the old beater station wagon with the flat in the picture? Looks like that old family truckster has seen better days.

lol...it's probably belongs to Bmw doubles seriously, when he revs it and takes off i was like holy crap there's not enough room!
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      03-20-2016, 10:36 AM   #5
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Quote:
Originally Posted by lsturbointeg
that's AWESOME bro! why was it your calves were the whitest things on the whole video screen? and for a second i thought you were gonna do your own rendition of "Fast n Furious" by launching off the parking lot garage anywho, the exhaust note actually sounds pretty damn good! and you thought of all this?? maybe patent this and market it ASAP! How are you able to determine how much exhaust is actually going out the open pipe...and is your undercarriage eventually gonna build up any carbon underneath?
Haha first off my white legs are damn sexy and that's the reason the videos works, secondly that was my audition for fast and furious performing a roof jump. I thought about making duplicates of the set up and selling them, but it's unproven and not dyno'd, yet. There's no carbon build up because I had custom turn downs fabricated so the exhaust points to the ground. Can't have a melted bumper. The percentage is a guess estimated by sound. Since I remember how freaking loud the delete was that was a calculation. It's 70-80% quieter then a full delete.

The wagon in the background does 1/4 miles in the low 3's

All seriousness, thanks for the props.
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      03-20-2016, 12:06 PM   #6
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Added cold start to original post ^^^
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      03-20-2016, 12:22 PM   #7
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Quote:
Originally Posted by lsturbointeg View Post
lol...it's probably belongs to Bmw doubles seriously, when he revs it and takes off i was like holy crap there's not enough room!
It did sound sweet didn't it?

I work for the company that owns the Automotive Exec of the Award in the US. In 2012 we gave the award to the then President of Ferrari North America. Ferrari had four or five new models in the parking lot for us to see and I got to fire up one of them, I forget which one. Their president told me they pipe the sound of the engine into the cabin up to a certain dB. I told my lovely bride when I get to the pearly gates, that may be the sound I hear coming from the Angels. There are few sounds in life better than the throaty roar of a well tuned, precision made car. (My wife's laugh, my dog's bark of joy when I come home, the tone of hearing 'hey dad' from my sons, the sound of Alabama's Bryant Denny Stadium on game day, and Lyle Lovett's voice being the only ones better)

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      03-20-2016, 12:42 PM   #8
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Quote:
Originally Posted by Jcbama85 View Post
It did sound sweet didn't it?

I work for the company that owns the Automotive Exec of the Award in the US. In 2012 we gave the award to the then President of Ferrari North America. Ferrari had four or five new models in the parking lot for us to see and I got to fire up one of them, I forget which one. Their president told me they pipe the sound of the engine into the cabin up to a certain dB. I told my lovely bride when I get to the pearly gates, that may be the sound I hear coming from the Angels. There are few sounds in life better than the throaty roar of a well tuned, precision made car. (My wife's laugh, my dog's bark of joy when I come home, the tone of hearing 'hey dad' from my sons, the sound of Alabama's Bryant Denny Stadium on game day, and Lyle Lovett's voice being the only ones better)

that's AWESOME!

for me the sweetest sound i love is when the ATM makes that dispensing sound and money comes out!
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      03-20-2016, 07:41 PM   #9
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BMW Doubles,

How many inches were your J pipe before you cut those? I have the Megan racing quad mufflers and a downpipe but there is to much drown for my liking. So I want to make J pipe fabricated.

Thanks
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      03-20-2016, 08:22 PM   #10
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Quote:
Originally Posted by Jayphil
BMW Doubles,

How many inches were your J pipe before you cut those? I have the Megan racing quad mufflers and a downpipe but there is to much drown for my liking. So I want to make J pipe fabricated.

Thanks
You have to know what frequency is driving you crazy. Download an audio frequency analyzer on your phone. Identify the frequency that is the most annoying. 80hz and lower is the cause of a "drone". That hum/ drone. Then once you've identified the frequency, insert that number into the Helmholtz equation

YOUR-NUNBER-HERE like this:

( 1100 / YOURNUNBERHERE.hz ) / 4 ) x 12 = LENGTH-OF-PIPE in inches needed to cancel annoying frequency.

My number ended up being 33"
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      03-20-2016, 08:26 PM   #11
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Also note I had the support exhaust bar removed and moved forward to accommodate the new j pipes y'd off the existing.
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      03-20-2016, 11:49 PM   #12
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Love the sound, great stuff as always! Just wondering if this will pass emissions test in your state?
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      03-21-2016, 12:14 AM   #13
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Agreed with others, very nice mod bro. The exhaust sounds really good.

On a side note: get some sun on those legs this summer bud
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      03-21-2016, 01:08 AM   #14
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Quote:
Originally Posted by Sedoy
Love the sound, great stuff as always! Just wondering if this will pass emissions test in your state?
I think it'll pass as long as my OEM DP is on.
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      03-21-2016, 06:54 AM   #15
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Quote:
Originally Posted by PJinCA View Post
Agreed with others, very nice mod bro. The exhaust sounds really good.

On a side note: get some sun on those legs this summer bud
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      03-21-2016, 11:50 AM   #16
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Quote:
Originally Posted by lsturbointeg
Quote:
Originally Posted by PJinCA View Post
Agreed with others, very nice mod bro. The exhaust sounds really good.

On a side note: get some sun on those legs this summer bud
I'm albino, but only on my legs
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      03-21-2016, 11:58 AM   #17
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Quote:
Originally Posted by Bmw doubles View Post
You have to know what frequency is driving you crazy. Download an audio frequency analyzer on your phone. Identify the frequency that is the most annoying. 80hz and lower is the cause of a "drone". That hum/ drone. Then once you've identified the frequency, insert that number into the Helmholtz equation

YOUR-NUNBER-HERE like this:

( 1100 / YOURNUNBERHERE.hz ) / 4 ) x 12 = LENGTH-OF-PIPE in inches needed to cancel annoying frequency.

My number ended up being 33"
My understanding is that for the same engine it will drone at the same frequency regardless of the exhaust. So if 33" works for you it should work for me but I will ask my exhaust guys to make the end tube +/- 3 inch adjustable so that I can tune it if needed.

Thanks!
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      03-21-2016, 07:14 PM   #18
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Jayphil just remember I used 2" j piping and moved the support bracket up to accommodate piping location and had it attached the j pipes.
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      03-22-2016, 05:16 PM   #19
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Jayphil just remember I used 2" j piping and moved the support bracket up to accommodate piping location and had it attached the j pipes.
Thanks for the close-up!
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      03-23-2016, 07:37 AM   #20
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clean work!
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      03-23-2016, 07:44 AM   #21
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stupid question but does the support bracket affect the drone / noise at all?
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      03-23-2016, 08:26 AM   #22
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i'm sure the name says it all...just holds the two pipes together. don't think it has anything to do with the drone?
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