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BMW 3-Series (E90 E92) Forum > E90 / E92 / E93 3-series Powertrain and Drivetrain Discussions > NA Engine (non-turbo) / Drivetrain / Exhaust Modifications > AA exhaust drone...



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      02-03-2014, 12:12 AM   #1
avocet
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AA exhaust drone...

well, my aa exhaust has droned since new. I have fiddled, and rehung, and changed hangars, and readjusted, and fiddled some more and rehung, and changed hangars...

I wasn't going to weld if the drone would not go away. a properly clamped exhaust will not cause drone. period.

yet the drone persisted. between 2000-2400ish rpm the drone could be miserable. especially in higher gears while under load. maybe if I lived in an area where there were no hills it would have been acceptable. but not here.

I used a plumbing block off for awhile to experiment. it dramatically reduced the drone, but it is blocking off one of the two exhaust tips. not something one should need to do with a fairly expensive piece of shiny pipe.

so it got me thinking. the power boat guys and hot rod guys use this thing called a spiral auger exhaust baffle. and because of the design, the actual flow cross section isn't reduced very much, so back pressure is not greatly increased. the biggest benefit, in my opinion, is that the sound waves can be bounced back at an angle and the cancel each other out as they bounce around. I ordered from JEGS for under 20 bucks, and lo and behold! my drone is reduced by 85%!!!

this thing is now usable. I have been waiting for a deal to come up so I could get rid of this aa exhaust, but now the drone is background noise instead of throbbing, rattle my door panel drone. and it is a little bit quieter at idle and other rpms... to my ear it sounds a little more mellow. a lot of the(unpleasant) raspyness is gone, but still allows that sweet snarl during throttle lifts.



this is a 3" diameter, but the metal was easy to grind down with a belt sander. I etched the spirals with a protractor, trimmed with some side cutters then finished on the sander. I also shortened the inner tube where it sticks out on the ends to be almost flush with the outside spirals.

I installed it where the aa exhaust mounts just aft of the axle. it was able to squeeze in there, with a slight tolerance fit. hammered it in just a little and it is in there tight. if down the road it rattles I will either tack weld it or add some small nut plates and bolt it in.

also, this is made from regular steel, so rust issues will loom down the road. not too worried... it is fairly easy to replace and cheap. there is another company making stainless augers, but are not cheap... 180$ or so if I recall. now that I know it works it might be a viable long term solution.



I can finally drive my car around without getting angry at it!!!

http://www.jegs.com/i/Dynatech/329/776-24302/10002/-1
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      02-03-2014, 12:18 AM   #2
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      02-03-2014, 12:27 AM   #3
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      02-03-2014, 12:35 AM   #4
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yes, I admit, I would love a PE setup. but my cards are already dealt. I found a cheap way to make what I have work for me.

it is what I do

I've diy'd everything on my car, from 335 brakes with functioning parking brakes to 3stage install to full suspension upgrades.

just sharing my experiences!

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      02-03-2014, 03:18 AM   #5
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Ingenious solution

I rode on a fairly long trip in a buddies car with this exhaust - halfway thru the trip I wanted to get out & walk the rest of the way

And this is with the special resonator that supposedly removes all drone - I still don't see how people with this exhaust can swear up & down that there is no drone...
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      02-03-2014, 09:46 AM   #6
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Personally I think AA's tune is great and they clearly know what they're doing, but they're parts are almost always less than great. Their e36 exhausts used to split now these rattle.. also do yourselves a favor and look up Spyder E90 BMW strut tower brace then compare it to the active autowerke one... striking similarities. No offense meant to active, I just think that they're much better at some things than others.
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      02-03-2014, 11:19 AM   #7
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:Smart solution to your problem, I have never had so called "drone" with my AA exhaust...

I can't even hear it when cruising.
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      02-06-2014, 04:06 PM   #8
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Quote:
Originally Posted by Dylanize View Post
:Smart solution to your problem, I have never had so called "drone" with my AA exhaust...

I can't even hear it when cruising.
I find this hard to believe. It does boom in a narrow band 2000 to 2400. If you driving a manual it's quite easy to manage.
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      02-06-2014, 04:22 PM   #9
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this is interesting, can you post a diy?
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      02-06-2014, 05:20 PM   #10
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Quote:
Originally Posted by SDemetris View Post
Personally I think AA's tune is great and they clearly know what they're doing, but they're parts are almost always less than great. Their e36 exhausts used to split now these rattle.. also do yourselves a favor and look up Spyder E90 BMW strut tower brace then compare it to the active autowerke one... striking similarities. No offense meant to active, I just think that they're much better at some things than others.
They copy us all the time exhaust, supercharger kits strut bars you name it.. Kind of like saying don't buy Oakley because people sell it on the street for 15 bucks.

Our e36 exhaust did have an issue awhile back from the heating and cooling of the metal causing a crack. All has been fixed now so I doubt you will find anyone with that issue anymore.


Cheers!
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      02-06-2014, 05:28 PM   #11
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good job. smart idea honestly Just do what i do and turn the music up. lol
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      02-07-2014, 07:22 PM   #12
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Quote:
Originally Posted by KwlAznKid View Post
this is interesting, can you post a diy?
what I PM'd you...

and for anyone else interested:


ya sorry didn't take any pics as I went... was kinda just tinkering with ideas and wasn't even sure how well it would work.

if you have the ability to jack your car up safely and remove your slip on exhaust, and have a few extra tools kicking around you should not have any issues with this.

extra tools must haves:
-hack saw
-tin snips
-decent file
-calipers or some way of marking the spiral... even an exacto blade would work
-bench grinder or belt sander(or if you are really patience, I suppose you could use the file... and you could just leave the cuts rough because no one will ever see it, and it won't really affect performance)
-hammer
-vernier caliper or some way to measure the diameters of the inside of oem pipe and the outside diameter of the spiral auger

and what I did in a nut shell:

remove slip on exhaust. measure inside diameter of the STOCK pipe that is still on the car. this is the dimension you will be cutting to. the AA exhaust is larger diameter, and the slip joint will be marginally thicker because it needs to slip over stock pipe.

then measure the outside diameter of the spiral baffle. this can be a little tricky because it is, after all. a spiral. a flat surface and a straight edge helps in measuring. don't worry, absolute precision isn't really required. but cut on the big side.

after you get both measurements, find the difference and divide by two. this is the amount you want to measure and cut off the spiral. I used a caliper to lightly etch the spiral. once marked, I trimmed close to the line with some tin snips, then finished off with a belt sander.

then I cut the inner length pipe of the auger off that was longer than the spiral section. this is so it could go deeper into the pipe without getting bottomed out on the bends quite as soon.

back and forth to the grinder until I felt the aa exhaust would fit over the spiral that was now sticking out of the oem pipe by a few inches. took a few test fits... you will see as you rotate the spiral it will want to go deeper and slight cock off at an angle. you want to go as deep as possible while keeping straight. if it goes off angle, the aa exhaust will not slip over and go far enough on to allow proper clamping.

once I knew it was going to work, I lightly tapped the spiral into the oem pipe still on the car until it was snug and I couldn't pull it out. I didn't do any more that this because I wasn't sure how well it would work out.

so far it's been a few hundred km's and no issues with rattles or coming loose in any way.

and almost zero drone!!!!!!!!!!!!!!!!

sure, I can induce drone buy getting into just the right loading and rpm while flooring the throttle. but even then it is waaaaay quieter, and during normal driving I don't experience it at all.

seat of the pants power loss? none that I can tell. I would even suggest it has flattened out the power delivery past 4000rpm. my car with a manual, aa tune and aa exhaust would have a major torque spike as I went through the 4200~rpm range. seems to have mellow a bit.

but realistically, any power loss that may have occurred is not noticeable, and the drivability is infinity better.



good luck if you try this and let me know if you have any issues or more questions!
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