Interior noise reduction - surprising results!!!

[Jonny042]

Hello all,

I have been chasing interior noise reduction in my car for the last two driving seasons - really my car has been quite painful to drive, requiring earplugs for trips of any duration on the highway.

I have posted a few "is this normal?" kind of threads, and really, I have wondered, over and over, how on earth Porsche could ever have sold a car that was this noisy. Most of the problem comes from the rear,engine noise. So I've really been working away on it lately, stripped the interior down to nothing in the rear, and performed the following:

- stripped off all the original yellow glue (using lacquer thinner mostly)
- added 3 heavy coats of "quietcar" sound deadener
- dynamat (approx 30-40% coverage, more on back shelf)
- closed cell foam lining side and rear panels
- mlv (mass loaded vinyl) sound blocker, 2 layers, to replace old sound blanket
- retained old sound pad on rear seat area (seems like a good design and should be effective, hard to do better!)
- re-installed everything else including carpet, and rear seats (which I have found do help with noise a bit when they are up).

I've been careful to weigh all of my materials and I have added less than 10 pounds to the car overall.

I was pleased with the results, and as I was driving on surface streets to get to the highway I was thinking it made a big difference, and it did, but once back on the highway, same old story, a funny whiny resonance from 2800-3000rpm coupled with an overly boomy sound from the intake/exhaust, still bad enough to give you a dull headache after an hour or so, and loud enough to make conversation difficult and make my Mcintosh stereo completely useless. Still all this sound reduction stuff does work and my car feels great, the door close with a wonderful solid sound, and I can barely hear the G50 whine anymore.

So I was pretty frustrated with all this hard work getting me small improvements but still not meeting my objective - to be able to take a nice relaxing road trip with my Gal, sans ear protection. I maintain that it should be possible to do that in a "high-end" sprts car, even if it's from 1987. It's one of the reasons I bought the car!!

A few weeks ago as I was scouring the board for ideas and found someone stating that new engine mounts had quietened a noise from their engine, so I ordered brand new, genuine porsche engine mounts to replace the URO parts mounts that I replaced my originals with last spring (this part of a "while I'm in there" engine out blitz while replacing the clutch).

So, tonight, as a last ditch attempt I had two things planned, first, replace the mounts, and if that didn't work, put the stock cat back on in place of my M&K Euro pre-muff. Changing the mounts is a 15 minute job at most, and I could hardly believe my ears when I went out to test it.... like a NEW CAR. Really. That big of a difference.

When I compared the new mount to the old one, the old one had sagged and deformed to the point that the protrusion of the rubber at the top was less than half that of the new one. It is possible that I had over-torqued the old mounts when I installed them and that caused the engine support bar to wind up and tighten the mount but I think, plain and simple, the genuine mounts are that much more supple and soft. No ill effects, either, it's not like the motor is bouncing around to much or anything.

I'm really VERY happy. I was actually checking prices on 993's thinking I might have to upgrade/downgrade to one just to get a car that I could actually USE!!

[FJ40runr]

Excellent that you were able to sort things out...that said I can't help but note this as a red flag that my appreciation of extreme metal and proximity to race cars may in fact be taking a toll on my hearing!

[pingpong]

Jonny042, appreciated taking your time to explain what you did to your P, i have been there with few result as well, can drive you ... anyway thanks.

[Ronnie's.930]

Growing a pair would have solved your noise sensitivity problem and saved you quite a bit of work, too!

[Chuck.H]

FYI, regarding the rear engine support bar, Porsche has a tech bulletin that says after installing the engine, loosen the four bolts that hold the mount to the engine, presumably to take any 'wind-up' out of the mounts, and then re-tighten them. Sounds like a good idea, but I always forget to do it :-)

Chuck.H
'89 TurboLookTarga, 340k miles

[Jonny042]

Originally Posted by Ronnie's.930

Growing a pair would have solved your noise sensitivity problem and saved you quite a bit of work, too!

I have a pair but strangely enough they are not connected to my ears at all. You might want to get that checked out.

I did two seasons of racing where I DROVE my race car to a track 8 hours away, with tires and tools and gear in the back, then drove it home. Earplugs both ways. A car with zero interior paneling and all the sound deadening stripped out and nothing but a supertrap is outrageously loud!!

[Jonny042]

Originally Posted by Chuck.H

FYI, regarding the rear engine support bar, Porsche has a tech bulletin that says after installing the engine, loosen the four bolts that hold the mount to the engine, presumably to take any 'wind-up' out of the mounts, and then re-tighten them. Sounds like a good idea, but I always forget to do it :-)

Chuck.H
'89 TurboLookTarga, 340k miles

That's really interesting - that's why I mentioned the fact that perhaps my installation had something to do with it originally - even though the old mounts were sagged after a year and a half and 3000 miles, it's hard to see that they would cause such havoc all by themselves. I'm actually worried that after a short time the new mounts are going to do the same thing!

I was thinking of loosening then tightening all four mount bolts (2 at the trans end, 2 at the support bar) and re-tightening them, but will add the 4 bolts at the engine mount to my list. Presumably the TSB was in relation to a NVH issue?

[Chuck.H]

It says 'misalignment between engine and trans mounts may cause stress resulting in the transfer of transmission noise to the vehicle body'...

Sorry it's a tech tip not a TSB (like it matters). On page 52 of the Parts and Tech ref manual.

Chuck.H
'89 TurboLookTarga, 340k miles

[Dublinoh]

Thanks for the follow up...a couple easy things to try for the noisy G50 Carrera

[sc_rufctr]

FWIW... When I went to WEVO mounts, blue bushes my car became a lot noisier. WEVO now have black bushes which are softer/more compliant than the blue ones.

I haven't used them but I would imagine they're similar to the OEM sports mounts.

[hbueno]

Another approach is to keeo your 911 noisy and drive it when you feel "sporty" and buy a 928 for times when you want to drive in relative quiet. That's what I did.

Hugo

[Jonny042]

Originally Posted by Chuck.H

It says 'misalignment between engine and trans mounts may cause stress resulting in the transfer of transmission noise to the vehicle body'...

Sorry it's a tech tip not a TSB (like it matters). On page 52 of the Parts and Tech ref manual.

Chuck.H
'89 TurboLookTarga, 340k miles

Where does one get a copy of this parts and technical ref manual?

[aerodyn930]

+1, On that tip, We have performed this on numerous cars, Always makes a difference, Loosen all four bolts, re-torque to 29 ft./ lbs. in a cross patern,

Enjoy!,, Lou

[KNS]

It may have been me that posted the noise reduction with new engine mounts, I've mentioned it once or twice. It does make a difference - and use only Porsche factory mounts, I had some other brand before and they were sagging with only about a year on them.

[Bob Kontak]

Originally Posted by aerodyn930

+1, On that tip, We have performed this on numerous cars, Always makes a difference, Loosen all four bolts, re-torque to 29 ft./ lbs. in a cross patern,

Enjoy!,, Lou

Lou,

Isn't the torque in the 65 ft/lb range? I have not read the official tech tip but remember "The Bruce" stating this is an ok thing to do. Just don't remember the backing off of the torque values part.

[aerodyn930]

Hello Bob, The bolts at the engine mount crossbar to engine mount (M12x1.5) get torqued in the 65 FT./lbs. range, The bolts mentioned in the tech tips "bulletin" are the four hex head bolts (M10x18) holding the crossbar to the engine mount console.

Hope this helps, Lou

[JAR0023]

Originally Posted by aerodyn930

+1, On that tip, We have performed this on numerous cars, Always makes a difference, Loosen all four bolts, re-torque to 29 ft./ lbs. in a cross patern,

Enjoy!,, Lou

Learn something new every day. I replaced a pair of 27 year old motor mounts a couple of weeks ago and a couple of 10 year old trans mounts this past weekend. Looks like I have a little project for tonight.

J

[drtyler]

Is there a significant difference in the "German" brand mounts offered by Pelican Parts and the Genuine Porsche mounts (which are three times the cost, almost $90 compared to $27 or $22 depending on if stock or sport)?

Thanks,
Dane

[KNS]

drtyler,

I many cases the non-Porsche part is just fine but for motor mounts get the genuine Porsche factory part. I replaced my "German" mounts after about a year or so because they were sagging. Spend a little more and you'll only have to do it once. The difference in noise in the interior was less as well.

[drtyler]

KNS - do you recommend sport or stock mounts? Price seems to be the same for the Genuine Porsche part.