droning! what i can't hear you?
 

wow my ears are still howling,
and this is coming from a guy who owns a strait piped harley.

i finally got to put couple hundred k on my 99 boxster (top up), the droning is insane, where do i start?

i took a quick peak under today and every thing looks to be there cats / mufflers but how do i figure out if thy are stock or not?

it's not actually loud on start up or reeving while parked, but get it going down a road and it howls so loud me and the wife had to holler to each other at certain rpm ranges.

If you are experiencing strong drone below 3k rpm, I'll bet you have an aftermarket mufflers that keep each exhaust system of 3 cylinders on each side of the flat-6 engine separate from one another, all the way out to the dual tips.

Does your rear muffler look like this?
http://s22.postimg.org/4udd0rky9/image.jpg

If so, please consider some content I posted previously on another board:

"I went ahead and did some calculations [on a 986 exhaust system] using a tuned organ pipe harmonic equation, where I think the drone would be most affected by the presence (or lack) of a crossover that couples the two separate exhaust systems of the 3 cylinder banks. I measured (by eyeballing with measuring tape, and guesstimation) that there is in the ballpark of an 8 foot long overall exhaust path length, from the exhaust valve through the cylinder head ports, headers, and rest of exhaust system out to tailpipe. (That's 2.44 meters.) An assumption made is for the speed of sound of the exhaust gasses being 500 meters per second (based on an estimate that the average exhaust gas temperature would be about 500 F throughout the length of the system). And guess what frequency came up at being the 1st harmonic (the loudest and lowest)? 51hz at the exhaust valves per bank, which equates to 2,040 crank rpm."

Now if you had the stock muffler, it basically has an internal crossover that basically allows the two banks to freely (without encountering any baffles or significant restrictions) allow the two separate banks to freely communicate sound pressure and rarefaction waves:
http://www.evan.com/boxster/stock_cut_open_diagram2.jpg
Due to the alternate-bank firing pattern of the Porsche flat-6 boxer engine design, this factory exhaust system results in 1st order, ~2,040Hz frequency being substantially cancelled out.

funny, as soon as i read tuned pipe organ my brain jumped to pulse jet! because that's what it sounds like.
do you think i could run a balance pipe before the mufflers or am i looking at buying a new stock muffler?
do you know if there are (non fart can) aftermarket mufflers available ?

There are, but they are not cheap. I have the one below, and it doesn't drone at all. I got it for half that years ago. The prices are crazy now. Cheaper to just get a stock muffler and modify it for more sound by having a shop install bypass pipes. I show screen shots below instead of the link because this site automatically edits out other site links.

http://i869.photobucket.com/albums/a...pssjsjrefr.png
http://i869.photobucket.com/albums/a...ps9fqdjing.png
http://i869.photobucket.com/albums/a...psf6lj2z1r.png

http://i869.photobucket.com/albums/a...pssoweomta.jpg

You guys are making me nervous. Just bought a beluga. Actually I feel pretty good about it. Put on next Friday. Very excited. I think like beer, people want to think things are better due to the cost, but is the cost really worth the improvement? I'll report back next week. Actually just came in from a place and paid lover $5 for a Narragansett. Friend chose the place. I would have been happier paying 1.50 for a PBR. I guess it is the accountant in me.😄

I didn't pay a lover. That would have been more than 6 bucks.

yeah that's a bit of sticker shock.
i can pick up a used one shipped for around 300 canadian.
too bad, i love the sound/noise level but that droning is messing with my tinnitus.

I was pretty excited about my Beluga exhaust until I put it on. It actually sounded good from outside the car but was offensively loud inside, especially with the top up. The drone was nasty.

My Beluga sounded really good, and while I wouldn't call it drone, it was louder in the cabin between 2800-3000 RPM, which is right at my cruising RPM. A couple of notes:

When I first installed it, I didn't get the clamps properly sealed, it sounded awful, like a fart-can. After tightening up, it sounded really good. Then, after some time, I noticed the louder sound between 2800-3000 that I described above. I did a check, and retightened the exhaust clamps, and was able to get some tightening/turns on the fasteners. This quieted down the 2800-3000 noise with the top up and windows up quite a lot. But by this time I had bought that PSE from Seb in the classifieds here, and so decided to try that. I pre-sold the Beluga (to be shipped once I got my new muffler), and then the PSE got lost by UPS, so I sent my original OEM muffler to Darin Fister at FD Motorsports. Here it is:

http://986forum.com/forums/uploads02...1487945744.jpg

I went to uninstall the Beluga, and low and behold, a couple of the clamps (the ones at the muffler side) were loose again. I probably should have gotten new clamps (which I have since done) and also I read that the inlet pipes of aftermarket mufflers may be made of thinner metal and might not have the same OD as the OEM mufflers, so an old clamp with corroded threads may not be able to make a good seal. I bought my new clamps from Amazon, and will know this weekend whether they are correct:

https://www.amazon.com/gp/product/B00317DKWO/ref=oh_aui_detailpage_o03_s00?ie=UTF8&psc=1

These can probably be found locally at many auto parts stores.

I also have topspeed 2nd cat delete pipes, which I have read really reduce/eliminate the drone with these aftermarket mufflers. I never had it installed with the 2nd cats so I don't have a comparison.

I had the exact same experience. I had it installed without the secondary cats too. Anyone who tells you that setup isn't loud is either hard of hearing or used to having straight pipes on their cars. I can tell you its one of the louder aftermarket "exhausts" I've heard in person.

I cranked up the car last night with just the exhaust manifolds/integrated cats installed, and no 2nd cats, pipes, or muffler installed. I will try to share a video. Sounded like a boat or something. I don't see how somebody could drive with just straight pipes if it sounded anything like this...

You'd be surprised. Spend some time on a Subaru forum and you'll hear lots of people bragging that they daily drive with their new 3.5" turbo back straight pipe and "its not that bad" lol

With a turbo it's a different matter. I had open pipes on my s4, and the turbos kept it reasonably quiet... until the wastegates opened.

But yes, straight pipes on NA cars is usually pretty hard to tolerate for a long time.

Anyone know what the internal construction is like on the top speed/Che/beluga-style 986 aftermarket mufflers?

Im wondering if it's straight-through style or if there are baffles/compartments, etc. (A picture showing one cut open would be awesome!)

They have some type of fibre style packing inside as sometimes you will hear if these exhausts breaking down inside and blowing it out.

Well I'll give it a shot and report back next week. I'm still pretty excited.

Yes I think the aftermarket exhausts have glass packs and will emit some fiberglass like sparkly powder you will see on your bumper at first. The guidance I read was to rinse it off with a hose and do not wipe it off as the glass may make swirls and micro scratches.

http://986forum.com/forums/uploads02...1487991912.jpg
Sparkly. Came tonight.

Shiny!!!!!!!!!

Just doing some reading. Some guy Rontnak (986 board) put a 2x4" motorcycle baffle on one side of his aftermarket muffler. Would this work on a Beluga and is no welding involved? I am having mine installed next Friday so if this possibly might help, why not try. Also, there are many 2x4 motorcycle baffles ranging in price. Why would they be so different? Thanks.

I would try it stock and see how it goes. Maybe there is a,way to sandwich some high temp rubber washers where it mounts at the top to reduce harmonics, I just realized the OEM muffler is isolated at the top mounting.

Got the full NHP permance kit on mine, 200cell cats.
 

(^performance, hmm)

Wrapped from the headers all the way down to the twin mufflers. Not only it lowers the temp in the bay, it also did cancelled drone by 15~25% for sure. Still sounds amazing though... and couldn't think for a minute to cancel it all. Part of the fun

... or maybe not for someone who DD on a slow highway for 50~75 miles/day. Could be different in that case ;)

That wrap was pretty thick. If my memory is good it was a good 3~4mm thick.

Nine8Six, what is the wrap you mentioned? Curious. Thanks

Its called Exhaust Header Wrap or something like that... made out of fibers. or cheap asbestos who bloody knows; wear a mask and gloves if diy lollll Some says its not recommended and you should only use ceramic coating but when living 15,000km away from common sense the wrap is then ideal ;)

example:
2" 50Ft Roll Fiberglass Exhaust Header Pipe Heat Wrap Tape Black +10 Ties Kit | eBay

6~7+ year later, and still looking good. Better than ceramic, certainly 100+ cheaper :D

http://986forum.com/forums/uploads02/wrap1488099852.jpg

If you look around the muffler intake, that is rust forming (I think). So if your exhaust is a $4,000+ unit and you drive your sport car in the rain, then maybe the wrap is not for you. Looking at this pic above, I'd say Use With Caution!

Although perfect to 'reduce' drone a tad and the heat driven by those cheap made-in-taiwan pipes & cans ;)

You think the aftermarket Boxster muffler designs are a straight-through, glass-pack style, like this?

http://i1307.photobucket.com/albums/...psc7945f4b.jpg

I don't think I have any glass packing in my Dansk exhaust. I've had it for many years, and have never seen any powder residue come out of it.

Most if not all the 2 box twin tips are of this construction I'm pretty sure and look just like the 'Topspeed'. Most are similarly lightweight and from alibaba.com. I've had 2 exactly the same both 'branded' differently.

Regarding the same construction, were they priced the same?

In my case they were bought about 2 years apart 1 from an ebay auction and the other as a bundle of parts as second hand but originally from a Porsche independent parts shop. You can't compare the price. There is variation in the UK on the new price by even up to 100%. That sounds drastic but some are not much more than 200GBP.

This exhaust is a Jic-Magic purchased on ebay a couple years back. There is no drone from this exhaust. The only problem is two hangers broke off, had them welded and now ready to go back on. The temp exhaust, currently installed, has the 2800 to 3000 drone. Why the Jic-Magic has no drone is unknown. I always thought it was the longer pipes or maybe the way the mufflers are built.

http://i1146.photobucket.com/albums/...pshv4yspeo.jpg

http://i1146.photobucket.com/albums/...psgadfmp6w.jpg

Here is my Jic-Magic exhaust that doesn't drone. What did happen is a couple exhaust hangers broke off, but it has been on for about 4 years. Just had it welded and it's ready to go back on. Not sure why it doesn't drone but I think it's either the pipe length or the muffler construction. The temporary exhaust is the lesser expensive ebay ones and it has that 2800 to 3000 drone. It's not awful but it's there. The Jic-Magic sounds so much better than the temp ebay muffler, and can't wait to get it back on.

http://986forum.com/forums/uploads02...1488318471.jpg

http://986forum.com/forums/uploads02...1488318493.jpg

so if i delete the 2 rear cats, and wrap the sweet bejeasus out of the exaust system i will kill that droning???
if it will work, i am on it!

The only luck I've had with reducing drone was with my GHL exhaust. I used a cut down motorcycle baffle and it worked good. It did not completely eliminate the drone but it was not that noticeable and if you've ever heard a GHL the drone is deafening. I tried wrapping the pipes, but it didn't work for me.

http://986forum.com/forums/uploads02...1488330014.jpg

http://986forum.com/forums/uploads02...1488330029.jpg

what do you figure the baffles are doing?? as far as droning is concerned?

I'm not sure, but I used a similar baffle in my Harley. Quieted down my Harley so that's why I tried it and it worked. I know the diameter and length has a lot to do with it and probably just got lucky. I was also going to wrap the baffle with thin fiberglass but didn't need to.

I would speculate they are causing a restriction, which encourages less high sound pressure pulse to get out through the exhaust tips, and more of that sound energy to instead get sent across the crossover pipe (which *is* present in the GHL exhaust) so it can travel back up the other 3-cylinder bank exhaust pipe, so that the rarefaction phase of this pulse effectively cancel out the positive pulse of the exhaust gasses escaping out past the valves of the opposite cylinder bank, at the "droning" (1st order harmonic) frequency.

Would the added restriction also rob horsepower, though, and defeat the purpose of having an aftermarket "straight through" exhaust system in the first place? In the absence of having dyno data to review, I would also speculate "yes."

good point, but the strait through came with the car, i am just trying to tame it .

That Jic-Magic exhaust looks similar in design to the Magnex one. I struggled to find a picture of it and I think it's discontinued now anyway. Rather than go straight through the box acts like a mixing chamber. The Janspeed, probably also discontinued, like the PSE have a similar design albeit one large box.

44FD1FD1-7618-4317-8A87-50225CA797AE-2115-000003AC666AC777.jpg Photo by sick_weirdo | Photobucket

If you want to cut the drone down you need chambered silencers in your system.