Correct exhaust mounting = drone fix!!

In a prevous thread I gave my initial impressions of the Remus exhaust on my 2.7 manual Cayman - all being wonderful with exception of the exhaust hanging way too low, a metallic vibration around 2,000 rpm; and although I wasn't too disturbed by the 2-2,800rpm drone wondered if it could be improved one way or another. Owing to the huge benefits I found through correct tension mounting of the exhaust (link to article below), I thought I should start a new thread both for Remus owners and others who have after market exhausts that use the OEM mounting points. Well, thanks to this website and the below excellent article, I firstly set about getting the mufflers and exhaust tips to sit at their correct height: Milltek, AWE, FabSpeed, - Articles I put the car onto ramps (approx 30cm high) loosened the relevant exhaust sections and mounting bolts, raised each muffler can separately with a normal car jack, tightened everything up again and re-aligned the exhaust tips. WOW - low hanging exhaust problem easily fixed - the tips sit perfectly in the housing now and everything looks just right. I had also previously noted that my metallic vibration (a bit drone-ish, but a little different) around 2,000rpm actually got worse after everything had heated up, whereas maybe I would have expected the opposite? I soon wondered if it could be the independent Remus exhaust tips vibrating together. This proved to be correct - the tips were sitting about 3-5 mm apart when everything was cold, but then were virtually touching at idle when hot; then obviously under load at certain rpm they found a way to touch. It proved to be quite difficult to slide the exhaust tip pipes further towards their respective muffler cans to widen the tip distance, so I jiggled it around as much as I could and slipped a washer in between the exhaust tip parallel mounting bars before bolting them back together (Remus owners will know what I mean here) which widened the tips-gap a little further - just enough to keep the tips apart when hot and therefore kill off the annoying vibration. BUT... the best discovery of all was that raising the height of the muffler cans, per article above, and therefore increasing the tension of the exhaust mounting has SIGNIFICANTLY improved the drone. In my case this either suggests that a good proportion of the actual "drone" was due to uneccessary vibration of the exhaust, not inherent in the exhaust design as I prevously thought - and easily fixed through correct tension mounting; Or that what I attributed to drone was just excessive vibration in a poorly mounted exhaust. I suspect it is the former as although the Remus exhausts are known to have some drone, I can now happily say that if you had sat me in the car with the Remus correctly mounted in the first place, I would not have said "what is that noise between 2-3,000rpm?" because it is really quite insignificant now - sure, a bit more volume (as distinct from "noise"), but certainly not the aural or cabin vibrations going on as some Remus owners have previously cited. So I suspect my fix might be their fix too. A final 'performance' note after living with the exhaust for a few weeks - definitely some extra seat of the pants horses and torque in the 3-5k rpm mid-range, and this has me shifting gears often earlier than what I used to, when driving enthusiastically. And spending a bit of time under the car with those ugly OEM headers in view has got me thinking about some good after market headers with high flow cats.. But that's for another day - right now I'm loving my correctly fitted, beautifully growling, low-drone exhaust - kind of like a 2nd marriage to the same car after two and-a-bit years!

Great write-up and advice! Dave

Didn't you have the dealer install it original? I would send them a bill for the work you had to do to make the install right

Many thanks for your post and I will make this adjustment. I have already extended the tips about an inch beyond the bumper edge and also isolated the muffler hanger from the stock mounting bracket with rubber bushings, all to no avail. The reason I did not tension the stock mounting bracket, and I did know about this recommendation, was that nothing on this bracket was changed during the installation of the Remus system and I figured that the factory got it right when they built the car. I am wondering if we are all hearing the same thing that we call drone. Here is a description of what my Remus sounds like on a 2008 CS. If I am moving along in top gear (or any other gear ) anywhere in the 2-3k RPM range on level ground there is NO loud exhaust sound. In fact, it is just as quiet as with the stock muffler. However, if I accelerate even slightly there will be a loud humming sound and this sound will continue to 3K RPM and then smooth out to that wail we love all the way to red line. There is no metallic component just a loud humming/drone.

Yep, my local dealer did the install. They are generally good guys there and I like to keep on good terms with them so will just politely send them a description of how to fit the exhaust properly next time - no bill attached, but perhaps they might return the favour one day!

Definitely try the tension set-up - your "drone" under load is/was the same as mine (with exception of my additional metallic vibration). In addition to what the article suggests, specifically for the Remus you might also want to loosen the connection between the muffler cans and the de-cat pipe, as this will allow the whole system to twist correctly into place when you raise the mufflers, which might be at least another inch or so higher (mine was about 2 inches). Obviously your exhaust tips will need to be angled down slightly or flat depending on how much more height you get on the mufflers. Yeah, as far as I see it, the jury is out on how bad the "core drone" of this exhaust really is, and to what extent resolvable mechanical vibration is a contributing factor - in my case I can say it definitely was but this is just a sample of one, and perhaps others have had similar experiences that can increase the sample size? I also recall reading somewhere that drone is sometimes less on the 2.7 than the 3.4, though I can't be sure about this, nor can think of a reason why this would be the case?? BTW - how did you extend the tips out - have you posted it on this site somewhere? I would be interested in doing that purely for aesthetic purposes as the tips on the Remus do not sit flush with the end of the exhaust tip housing like my OEM sports tips did. I don't like those after market tips that extend too far beyond the rear of the car (looks like weaponary James Bond would fit to his Aston) but there is a balanace in there somewhere! Cheers

Very useful details Briscayman, thanks for putting this together. Graeme

BTW - how did you extend the tips out - have you posted it on this site somewhere? I would be interested in doing that purely for aesthetic purposes as the tips on the Remus do not sit flush with the end of the exhaust tip housing like my OEM sports tips did. I don't like those after market tips that extend too far beyond the rear of the car (looks like weaponary James Bond would fit to his Aston) but there is a balanace in there somewhere! Cheers[/QUOTE] The tips were extended by moving the entire muffler rearward. This was accomplished by inserting silicone rubber spacers between the muffler mounting bracket and the car mounting bracket. The rubber I chose is quite stiff and being silicone, head is not a problem.

I have the same going on with my '06 CS w/ the cat-back borla - the drone gets appreciably worse after warm-up; I'd *really* like to know what's tightening up when the car warms up. On another note (RRR) the acura ads showing how they use active noise cancellation got me thinking - it may be quite easy to implement a drone-killing signal to send thru the stock stereo -- capture the freq. and phase of the drone as it's happening, invert the phase and feed it thru the car stereo to the subwoofer. I'm not sure the sub can reproduce a note that low but it could work great on the harmonics. mmmv, -PM.

Just an update. The tensioning of the muffler hanger did nothing to reduce the drone, at least in my case. With respect to warmup increasing the drone, a previous thread suggested that it is the result of the change in the speed of sound in air with the change in the exhaust temperature, drone being a function of tuned pipe resonance. This is becoming my theory of choice since all my attempts at reduction by mechanical isolation have failed to produce a positive result. I am at the point of accepting that it is what it is. There is a resonant point between 2 and 3K RPM that is just there and nothing much can be done about it. Step lightly in that range and you're OK. Hit it hard and you are going to hear an unpleasant sound.

I'm reviving this thread as I'm tired of hearing my droning borla and found a thread on the 370Z board which details an actual fix, accompanied w/ an explanation containing Math and Real Science. Briefly it entails adding a 'side branch resonator' to the plumbing between the exhaust tip and each muffler (for my borla that's 1 resonator / side). it's spectacularly low-tech -- a tube T'd into the exhaust piping as described and closed at the other end. The trick is to tune the length. Read all about it HERE! Other than tuning the length the other challenge is to find room for each side's resonator -- there's room from the tips back to the engine so I may try to get an add'l tip section from borla and modify that, welding it up tight when I have the length right. I'll do the math but I expect it to come out the the 26" - 28" they used. depends on the # of ignitions per revolution they have w/ their V6. We have 3.

and while I'm droning on about this (rrr) - Does anyone know the actual drone frequence -- that resonant frequency at which the body vibrates ? Thanks !

Very interesting. Be sure to post the results.

Thanks for the write up Briscayman. If you are in the market for some high flow cats maybe you could cast your eye over these: Porsche Cayman Exhaust | Caymen Sports Exhausts Inc OE Porsche & Milltek I've been trying to draw some opinions from people before taking the plunge but my threads have gone unaswered to date. The price and quality looks very good but I don't really have enough technical knowledge to know exactly what to look for....:cheers: /notices date of OP... sigh

What's your thinking behind the high flow cats?

I'm sure i read somewhere that HF cats and standard exhaust gives a good sound without drone, probably releases a few ponies too. I think I'd only change mine to HF in the case of an MOT failure though, going down the Carnewal route for sound without drone.

Surely a full decat "if you have the time and inclination" is a better way to go? you get a much better sound?

The problem with a full de-cat is that you may well get Check Engine Lights on the dash, at least this is my understanding.... hence my interest in a high flow solution. I'd be running the HF cats with the PSE so I dont think I'll be disappointed with the sound....

I suppose the HF cat does have the benefit of being legal, i just feel it probably isn't as pure as going "all the way" and opening her up

Mandrel-bent tubing!! God that sound makes me horny... Top 10 Exhaust Videos of August 2010 | Exhaust Videos

Can anyone help me with uploading pictures? I'm really sruggling to get my car pictures up here, please... X

Manage attachments button on reply screen. Click Browse and then upload when you have selected pic you want to upload. Jobs a goodun ........

This is by ear only and from what I'd expect someone to characterize drone to be. Frequency is likely in the 100 to 200 Hz range. I can't measure it for you as the Capristo just doesn't want to drone. While it may vibrate the body I suspect the drone is more a function of pipe length and the excitation from the exhaust pulses. At 2500 rpm there are 125 exhaust pulses per second. The pipes are very roughly 6 feet long or so. Depending on what temp you want to use for the average temp of the exhaust gases the speed of sound is 1600 ft/s for 500°F and higher as the temp increases. Since drone seems to be a part throttle thing I went on the low side. If the 6 ft pipe is half wave the pipe resonance freq comes out at 134 Hz using these rough numbers. Pretty easy to imagine having the exhaust impulses hitting the pipe resonance when accelerating at light throttle between 2000 and 3000 rpm. I suspect that getting the pipes out past the bumper just reduces the amount of reflected sound getting back into the car.

Hi I bought a TopGear exhaust for my 986 to replace the ratteling 20 yrs old original unit. See more on TopGear co uk. (996\ 986 catback exhaust with chrome tips). It was not easy to mount as I had to cut off brackets from old unit to use on the new (after modifying them a lot). Anyway, when finished it looked great and sounded great until test driving at 2-3krpm. The drone was so loud that I could almost not hear the stereo. However after searching on forums for solutions I found these units in the US. Car Chemstry 2» Inserts (type 3DI02R). I installed one of these in each SS 3« tip and the drone is now 100% gone! According to the documentation they provide there should not be a reduction in HP or torque. Sound is also nice. I could not find the exact size for the insert so I had to widen them abt 3-4mm (each disc). Fastened them with a 6mm SS bolt from below (drilled hole / threaded) in each pipe. If anyone is interested I can send pictures.

Pictures are prefered, especially if you can point out the inserts, but do not expect any of the above thread makers to respond, long gone.

Hi See attached pictures. I plan to paint the end cups black or possibly remove them entirely (to increase sound level a little). I drilled a 6mm hole in the midle disc on the insert to allow the 6mm bolt to enter from below to lock the unit in place. Sorry about the quality...it´s winter time and dark and cold these days...

What exactly does the insert do? Most of the extension I have seen, are just an extension of the exhaust pipe. Do they add back pressure?

Hi there. Check out Car Chemstry´s info here: Car Chemistry Inserts www.carchemistry.com

Got it. I like the most HP my little engine can produce at 6800 RPM. No restrictions, no cats, just a Milltek muffler, extensions and Soul long tube race headers, which sounds fantastic for a 3.4l M97. - response coming from my local speed shop, Cantrellmotorsports, lead technician.

Rehashing this.. TI0, Hows this after a few months? I have cabin drone from 2000 to 2600 rpm and wouldn'tmind signifiantly reducing it. Is this the part you ordered x 2? 3 Disk Insert: 2 3/4" Diameter Products to enhance automotive sound performance www.carchemistry.com How is it held in place? Your exhaust is all stock? Thanks.

Hi there, I'm still happy - no drone. Actually the exhaust is so silent that I'm considering to remove the two end covers (on the centre pipe) to open up a little. By they way I painted the insert black with HT black spray paint to make it look better. See picture. I have the TopGear exhaust (see more on TopGear co uk. (996\ 986 catback exhaust with chrome tips)) - the installation what not not strait forward.....but after a few evenings I got it installed. I drilled and threaded a 5mm hole from below in each tip and screwed in a short SS bolt (had to drill a hole in one of the discs in the insert - needs to be aligned).

Thanks for replying. So the 2 end caps are for fine tuning the sound. Cabin drone greatly reduced.. sounds good. How do you feel it has impacted power and at what range? Your headers are stock? What year and model is your ride? Thanks again.

Hi Correct. I have not noticed any reduced power (not using the car on a track...). 1998 model - tiptronic. Headers are stock.

Thanks again. At what it costs, no harm trying them. Stay safe.