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The world can never have too many exhausts for the 996T, but for those not into fabricating their own exhausts or resonators, I will just restate that I have had years of pleasure already from an aftermarket exhaust on my 996T - but only after putting a few concentrically stacked layers of Dynamat on the big unsupported metal panel surfaces of the firewall and parcel shelf.
I think I might try this, in addition to resonator pipes. I notice with stock exhaust back in now that there's a resonance at the same frequency. It's just nowhere near that painful volume level.
996tnz, exactly where did you put the dynamat? Is it on the horizontal surface below the DME and the other black boxes back there under the sub woofer? or on the vertical surface behind these just under the window? Or both? I put a layer of the thick fabric sound insulation in there and it had no appreciable effect. i understand the dynamat works by damping the surface vibrations rather that trying to insulate the sound created by the surface (a first order fix) i want to give it a try as my 02 is an occasional long haul commute vehicle and quiet is nice.
Hi Third-reef. Sorry I missed your question earlier but will answer for anyone still coming across this thread. It's just the big resonant panels (think like a drumskin - you can feel them flex if you push them), ie the firewall (vertically behind your back if sitting in the rear seats, between you and the engine), and the parcel shelf (the wide horizontal steel shelf just under the rear window).
While I was in there, I did also put a single layer of dynamat on the shiny stainless brackets that hold the ECU etc under the sub-woofer. Not because they might drone (they're much too small for that and aren't external boundary panels) but because I thought they might eventually buzz a bit and I didn't want to go back in again.
Hi Third-reef. Sorry I missed your question earlier but will answer for anyone still coming across this thread. It's just the big resonant panels (think like a drumskin - you can feel them flex if you push them), ie the firewall (vertically behind your back if sitting in the rear seats, between you and the engine), and the parcel shelf (the wide horizontal steel shelf just under the rear window).
While I was in there, I did also put a single layer of dynamat on the shiny stainless brackets that hold the ECU etc under the sub-woofer. Not because they might drone (they're much too small for that and aren't external boundary panels) but because I thought they might eventually buzz a bit and I didn't want to go back in again.
...I had this done by a sound shop with zero effect to my resonant drone...
I did it and it helped a little.
Swapping back to a stock helped a lot. I have a track day at Laguna Seca in July and the last time i was there i got black flagged for noise. I was about 98 db and the limit was 90. So for me the stock exhaust will be a performance improvement. Hoping to shave 4-5 sec off my lap times by not having to roll through turn 5 and up the hill to 6. Probably put my Kline back on for Thunderhill and Infenion latter this year. I can definitely feel the difference.
I've had and tried many exhausts. Some drone a lot, some less, very few none. It's all about the exhaust design. Most guys go to great lengths to mask exhaust drone. A proper exhaust design will eliminate it at the root. I have a 3" flow through exhaust with helmholz resonators on a 3.8L engine. All the sound deadening material has been removed from the car and all the insulation on carpeting has been removed also. Zero drone, zero resonance at any rpm.
I've had and tried many exhausts. Some drone a lot, some less, very few none. It's all about the exhaust design. Most guys go to great lengths to mask exhaust drone. A proper exhaust design will eliminate it at the root. I have a 3" flow through exhaust with helmholz resonators on a 3.8L engine. All the sound deadening material has been removed from the car and all the insulation on carpeting has been removed also. Zero drone, zero resonance at any rpm.
...I had this done by a sound shop with zero effect to my resonant drone...
Sorry to hear that Mark. Did they stack it 3 to 5 layers deep in the middle of the panel, tapering off to one layer deep a third or so of the way out to the edge? Or did they just put one or two layers of Dynamat all over the whole panel, as sound shops typically do? I suspect that covering the whole panel might just see it resonate at a lower frequency than before.
I placed decreasing concentric circles of Dynamat on the middle of the parcel shelf and the firewall flexible steel panels, ie something like 12 inch, 10 inch , 8 ,6,4 or something like that, plus one layer right over the top of them all. That puts most of the mass in the middle of the 'bass driver' - ie middle of the flexible panel, where it can best damp the resonance.
The difference for me was between a car that made me nauseous within a few miles (almost to the point of vomiting), to one I can drive hundreds of miles a day. Because I know that shallow 'hill' of stacked Dynamat is there, I can see a slight rise in the parcel shelf when looking for it, but it's hardly noticeable visually.
It didn't make the exhaust noticeably quieter inside (that wasn't the goal) but it did stop it thrumming and resonating through the cabin in that way that made me nauseous (like some warbling burglar alarms can too). Made the difference between me hating my exhaust and me loving it - for the sake of 50 odd bucks and an hour or two of labour.
I may be able to find some pics from my install on my old mobile to demonstrate it better, but below are my earlier posts from other threads if that helps any - with apologies for some repetitions:
Originally Posted by 996tnz
...
Mine has a 70mm REMUS exhaust with metal HJS cats that I run with Kevin's tune. Great power and awesomely deep mellow bass but you will want to lift the rear trim and apply some sound damping Dynamat (just half a door kit is plenty) to the centers of the big firewall and parcel shelf panels to tune out the 2000-2200rpm drone on a 996T. The Dynamat sorts that nicely and leaves a great sounding 98dB exhaust rumble down low that still screams at high revs too. REMUS provided the exhausts for the Dauer 962 so have history with Porsche. No tunnel is ever safe!
As long as it is sticky, heavy and flexible it should work but I just used the standard Dynamat product. Something like $40 or so IIRC.
Yes, do the firewall and parcel shelf - both behind the rear seats. Just unscrew and remove the seats, pop out the Bose speaker grilles, remove the two allen bolts holding the Bose in place, slide it forwards gently and unclip the electrical connector (the only fiddly bit as it has a little retaining lug but it is pretty solid so little chance of breakage). There may be a couple more simple brackets to remove IIRC then just pull all the foam-backed carpet trim sheets out and get to work. Those are all just pressure fit, with the parcel shelf one wedged in fairly tightly so I think I just pushed it up and worked underneath it.
If you track or canyon your car you'll want to minimise the weight you add, hence the tip to concentrate the most layers towards the middle of those big panels. I stacked them concentrically like a contoured hill covering about a quarter of the surface area then put a single layer over the top to tidy it and provide a little extra damping. Figured there was no point adding more weight by putting lots of layers all over everything as it doesn't primarily isolate or absorb sound. As I said, with you being an engineer I'm sure you know it already, but in case this doesn't make sense to anyone, it basically works in the same way as sticking a pound of softish butter to the middle of a drum skin, damping vibrations and lowering their frequency down to where they no longer resonate in an irritating way.
Just reverse the access procedure to put it back together, but its like Lego really so will be dead obvious.
Originally Posted by uschoice
That Dynamat mat sounds promising.
Haven't heard that suggestion before.
Originally Posted by 996tnz
Worked a treat. Felt odd to be placing some weight into the car that high up but there was no way I could use the car for family runs without it, and even the drive to work was a chore with that nauseating cruising speed drone.
Dynamat works by mass damping, rather than by acoustic isolation, so you only need to concentrate it in the middle of the big resonant firewall and parcel shelf panels rather than trying to swathe the whole area in lots of it to 'block' sound. Think of it as putting a dive weight on the middle of a drum skin to dull out the drum by stopping it resonating, as opposed to smothering it under a duvet.
Less than ten pounds of the stuff was needed, with about 3 tapered layers in the middle of those panels and one over the top to smooth and tidy things. I also put a little bit on the tray that covers the ECU but it probably wasn't needed.
The REMUS always sounded great from the outside (some pit crews wondered if it was naturally aspirated) but needed that bit of help to sound good from the inside.
Not to be a dick but who drives for long in this range?
I had a problem with my exhaust drone when I first put it on and was advised to stop babying the car (lugging was the term) and ramp the RPM's. Now I rarely shift before 3500 RPMs (usually 4K+) and can't get enough of the sound. IMHO if you're at cruising at 2000-2200 RPMs you're in the wrong gear.
Not to be a dick but who drives for long in this range?
I had a problem with my exhaust drone when I first put it on and was advised to stop babying the car (lugging was the term) and ramp the RPM's. Now I rarely shift before 3500 RPMs (usually 4K+) and can't get enough of the sound. IMHO if you're at cruising at 2000-2200 RPMs you're in the wrong gear.
Guessing you don't commute much in traffic? Or drive a Tip?
BTW, here's a bit of an explanation from one of Dynamat's competitors:
"Here is a brief description of the materials used in acoustic management:
Damping is the reduction of vibration and noise generated by resonant vibration in areas like body panels, door panels, floor pans and roof panels. Damping material should be at least one-half the thickness of the metal or composite material to which it is being applied and cover approximately a 25 to 30 percent of the surface area. The most effective material used in damping is a self-adhesive rubberized asphalt material that is acoustically “dead” because of its dense mass and weight—about two pounds per square foot. The best automotive dampers are water repellent.
Absorbers are materials that do not block sound, but rather, "soak up" sound and prevent sound waves from reflecting. Absorbers are made up of dense fiberous materials with open pores. Open cell foams, shoddy, fiberglass and fibertech are examples of sound absorbing materials. Thick materials absorb low to high frequencies: thin materials mainly absorb medium and high frequencies."
Porsches own soundproofing in these areas is of the absorber kind being foam. We're just adding that damping underneath.
For those with some technical interest, here's a pretty readable explanation, that also points out that 50% coverage is 97% of effective as full coverage when it comes to damping a panel:
Not to be a dick but who drives for long in this range?
I had a problem with my exhaust drone when I first put it on and was advised to stop babying the car (lugging was the term) and ramp the RPM's. Now I rarely shift before 3500 RPMs (usually 4K+) and can't get enough of the sound. IMHO if you're at cruising at 2000-2200 RPMs you're in the wrong gear.
Most roads in Europe have a limit of 55 mph, meaning that a 996 Turbo will do about 2000-2200 rpm's in 6th gear. You're telling me that I need to stay out of 6th gear if I make a 300 mile trip?
Did Porsche specifically tell its customers that the 996 Turbo isn't built to handle 2000 rpm's?
Driving on a nice flat road will do no harm whatsoever. If you're going uphill or need to pass someone then just downshift, it's easier for the engine but also safer for you to make that pass as fast as possible.
Only what to actually eliminate all drone and have a loud and nice sounding exhaust I with anti drone tubes. I built identical systems, one with without the tubes and ones with, having them solves all the issues.
If you have a system on the car already, any decent exhaust shop could add these to your current system.
Anti-drone tubes? That is incredible. How much volume do you think comes out of the tubes? Just a resonance or a volume of exhaust gasses?...any concern of engine compartment heat-up from dumping some of the exhaust into the engine compartment?
And any sound clips? This appears catless as well so it has to sound bad-***.
thanks
joe
Originally Posted by Flewis763
Only what to actually eliminate all drone and have a loud and nice sounding exhaust I with anti drone tubes. I built identical systems, one with without the tubes and ones with, having them solves all the issues.
If you have a system on the car already, any decent exhaust shop could add these to your current system.
Most roads in Europe have a limit of 55 mph, meaning that a 996 Turbo will do about 2000-2200 rpm's in 6th gear. You're telling me that I need to stay out of 6th gear if I make a 300 mile trip?
Did Porsche specifically tell its customers that the 996 Turbo isn't built to handle 2000 rpm's?
Driving on a nice flat road will do no harm whatsoever. If you're going uphill or need to pass someone then just downshift, it's easier for the engine but also safer for you to make that pass as fast as possible.
I almost never use 6th unless I'm trying to save gas or something but I also like the way my exhaust sounds.
04-29-2017, 09:27 PM
