droning! what i can't hear you?

[madmac]

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.

[jakeru]

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?


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:

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.

[madmac]

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 ?

[Boxtaboy]

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.

[DWBOX2000]

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.😄

[DWBOX2000]

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

[madmac]

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.

[pilut2]

Originally Posted by DWBOX2000

You guys are making me nervous. Just bought a beluga. Actually I feel pretty good about it.

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.

[steved0x]

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:



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.

[boxxster]

Originally Posted by pilut2

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.

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.

[steved0x]

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...

[boxxster]

Originally Posted by steved0x

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

[alm001]

Originally Posted by boxxster

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.

[jakeru]

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!)

[edc]

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

[DWBOX2000]

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

[steved0x]

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.

[DWBOX2000]

Sparkly. Came tonight.

[steved0x]

Shiny!!!!!!!!!

[DWBOX2000]

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.