Engine Sounds Mat Question

[Kaliv]

I was told that 911's are loud, and mine seems to fit that to a 'T'. When I took my wife for a ride, she enjoyed the ride but said the car was too loud and when she talked she said she sounded like a robot.

The Car-
The car is an '87 with some aftermarket mass air flow filter and a sports muffler, it is dual exhaust. The engine compartment has no sound mat in it.

So I'm thinking, to solve the problem, I need to install a real good sound mat. Do you think this will but down a lot of noise? I could always install a stock exhaust, but I like the dual look and want to do that as last resort. How much noise reduction do you think the sound mat will give?

Also, I'm looking at the two different mats sold by our host. How much difference do you think I'll get by using the OEM 911-556-891-01-M136 over the Foil Engine Compartment Sound Mat/Pad PEL-APBZ-ESPU. I don't quite understand how putting foil on a pad is going to make much of a difference...but if it does, I'll do that.

Anyone have experience in this area and do you think it'll be worth the upgrade or should I attack the sound problem from a different angle? I did a quick search and it looks like I could put thinker soundproofing pads under the rear seats...but I just reinstalled the seats and don't want to take them back out. Also, someone said a lot of high frequency noise comes in through the back air vents, but I'm thinking low frequency noise is my bigger problem.

[randywebb]

a sound mat will help - I have never seen any data to show that any aftermarket item is better than the stock one

do a search for threads on this

you can dump the aftermarket air cleaner and put the stock induction unit on - that will provide better air filtration and get rid of the induction howl

a cow horn type dual out muffler will give you less noise than a real sport muffler and as much power if not more (depends on how the mufflers are made - many aftermarket ones lose power)

finally - invest 200 hours of your labor in sound proofing the interior side of the firewall - search for Jerry Hubka's thread where he did that and explained it all in great detail (jhubs)

[Kaliv]

Yeah, I saw the thread on what jhubs did to his car. That was awesome. But I don't have nearly the amount of time to invest into a project like that. And seeing how this is my first year owning a Porsche, I want it on the road as much as possible instead of sitting in my garage with peices missing out of it.

Anyone else with information on how much dampening a sound mat provides and if buying the foil one is worth the extra cash?

[jhubs]

Kaliv,
I would put the engine compartment sound mat in as a start. The ones from our host are good ones. The issue is getting it in there...tight fit but it will reduce heat and noise. IMHO, I would spend the money on the Foil one. I know it is more money, but the sound felt pad should be better than foam.

jhubs
Jerry Hubka

[KFC911]

I've only got a single out sport exhaust, and my car is just the way I like it. Seriously, when I removed my sound deadening pad, I couldn't tell that much difference, so I'm not sure adding one back (in your case) is going to make the sound tolerable for your wife. Maybe you should try blocking off the second outlet (when she's in the car) first to see if that is a solution. It'd suck to install the sound deadening (a real PITA I'm sure) just to find it doesn't compensate enough for your dual exhaust...hey, they're 'sposed to be loud

[Rot 911]

I'm with KC911. I listened to the sound of my exhaust before and after the installation of a new sound pad and really couldn't tell the difference. I would first try blocking off the second outlet and see if the noise level is tolerable to your wife. If not, the cheapest and easiest way to a quieter exhaust is to put back on the stock single outlet muffler.

[sjf911]

Single out stock muffler would be the quietest. I had a single out sport muffler and felt it was too loud (with intact sound proofing/engine mat) even with the catalytic converter. The cat bypass pipe made it worse.

[Kaliv]

Ok, taking this thread in a different direction I guess. It sounds as though I may need to change my exhaust to get the quieter sound I want.

So I went out and looked at the extra exhaust that came with the car. Looks to be stock with the muffler being 93011104300 and the heat exchanger being 93021102901. Seeing how it looks like the rear valence of my car has already been modified and the fact that I like the look, I would like to keep a dual out, which this setup does not provide.

I'm not sure what is on the car right now as I can't find any numbers on it, but the muffler is definitely a dual inlet dual outlet muffler and what appears to be 3 1/2 inch tips. Not sure what brand it is or even where to look for the numbers with it installed on the car. Any ideas where to find out? Anyway, it kind of looks like this picture but with two inlets:



I can't find a picture of the heat exchangers or headers or whatever it's called. All the pictures have pipes that are side by side horizontally, and the pipes on my car are kind of one on top of the other.

Anyway, what would you recommend with the parts that I have to change out keeping money at the minimum and silencing effect at the maximum. That and keep in consideration that I want a dual outlet look so I don't have a gaping hole of nothing.

And will changing the exhaust need me to change the performance chip in my car. I think it's some AutoThority chip because the OEM one is in a box labeled that. I can't remember if the PO said I would need to put in the old chip if I changed the exhaust or if I swapped out the aftermarket mass air flow sensor unit.

[mschuep]

One thing you should consider before changing anything is where the noise is coming from. If you hear exhaust noise, focus on exhaust attenuation...If it is engine noise that you hear, focus on engine noise attenuation. You can try a sound pad, but as others have said, and I would say, they really don't do a whole lot by themselves.

My guess is that you have an aftermarket dual inlet/outlet muffler, which is louder than stock, and it is resonating at certain frequencies when you are cruising around town, which makes your wife sound like a robot.

The second part of your post about the aftermarket chip and the MAF and the exhaust is a different question altogether, and opens up a big bag of worms...but it is definitely something you need to consider should you elect to go with a different exhaust, as this will likely change exhaust backpressure, etc.

Lastly, I would mention that the car might never get as quiet as you or your wife might want. It's not a pleasure cruiser, its a performace sports car. If you can find someone in the area with a 84-89 carrera with a stock exhaust and engine pad, I would see if they would take you for a ride before you blow money on trying to make the car quieter.

[KFC911]

Originally posted by mschuep
Lastly, I would mention that the car might never get as quiet as you or your wife might want. It's not a pleasure cruiser, its a performace sports car. If you can find someone in the area with a 84-89 carrera with a stock exhaust and engine pad, I would see if they would take you for a ride before you blow money on trying to make the car quieter.

I agree, any sport exhaust is going to sound like a sports car should, but imo, the stock setup is VERY tame by comparison.

[Kaliv]

What exactly makes the exhaust system so different in noise level? Would I be able to swap out a muffler and quiet it down, or doesn't it work like that? I'm have no idea if the muffler and heat exchanger need to be replaced together or if you can mix and match. What makes more noise, heat exchangers or mufflers?

[coldstart]

I would say the muffler is responsible for ~90% of the noise. Heat exchangers, unless they are in horrific shape and are causing backfiring, are not normally noisy.

[Kaliv]

Originally posted by Kurt V
I would first try blocking off the second outlet and see if the noise level is tolerable to your wife.

Ok, guess I didn't quite understand what you were talking about. Was doing more research on mufflers and some people are saying that there are caps out there to put on the passenger side exhaust pipe that makes the muffler quite a bit more quiet. Is there a technical name for this piece as I couldn't find anything to order. What do I need to know to order myself one, just the diameter of my muffler tips?

One other thing...will capping cause backpressure?

[MattAlpha]

When I removed my OEM foam pad (which was starting to fall apart) I did notice a slight louder engine sound. I have a cab, so it doesn't bother me. I would go with the foil over the foam.
-Matt

[sjf911]

The engine compartment pad appears to primarily function as thermal insulation with additive sound attenuation to the heavy layers of sound deadening material inside the cabin under the rear seats and deck.
Headers increase sound essentially by removing the premuffler or catalytic converter from the circuit. Also, they do reduce the average exhaust path length and may optimize the acoustic path.
Dual outlets do increase noise (about 6dB according to M&K) but the effect on resonance in certain RPM's is apparently more bothersome to some people than simply the volume. M&K sell a cap for their dual outlet muffler, but I think you have to contact them directly. Otherwise, you have to improvise one for yourself.
I personally find the OEM muffler the best for all around driving. You can hear the mechanical sounds of the engine much better (fan, cam chains, induction, etc.).

[randywebb]

make a cap for the RH side pipe

search for threads on how others have done this

[Kaliv]

Posting some pics of the system I am currently working with. Sorry they aren't very good, I have no way of jacking the car up to get a better view.

[KFC911]

Contact Ben at M&K (his contact info will easily be found here on Pelican), and I'm sure he'll be able to fix you up with a cap. If that doesn't quiet it down enough for your wife, then a stock muffler is what you need.

Keith
'88 CE coupe

[randywebb]

Bingo.