Road Noise
05-10-2016, 04:22 PM
#18
Intermediate
Join Date: Apr 2015
Location: Southern Ontario
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There are a lot of different sources of noise.
Road noise/rumble: I found a tremendous difference is made by the tires. When I got my '90 it had 10 year old Dunlops that had plenty of tread but had hardened. New Bridgestones subjectively reduced road noise by half.
Additional insulation in the footwells - Dynamat/B-Quiet or similar, with acoustic foam on top also made a big difference to road noise transmission. Likewise foam under the hatch carpet.
Wind noise: The windshield noise is more of a whistling noise, and Roger's rubber strips (modelled after the factory strips added to the GTS) address this somewhat.
A lot of other things such as door and hatch strips, side window adjustment, b-pillar foaming, wheel wheel liners, etc. can all make a difference. My '90 is now relatively quiet, but not to the standard of new cars - it's an old car afterall.
Road noise/rumble: I found a tremendous difference is made by the tires. When I got my '90 it had 10 year old Dunlops that had plenty of tread but had hardened. New Bridgestones subjectively reduced road noise by half.
Additional insulation in the footwells - Dynamat/B-Quiet or similar, with acoustic foam on top also made a big difference to road noise transmission. Likewise foam under the hatch carpet.
Wind noise: The windshield noise is more of a whistling noise, and Roger's rubber strips (modelled after the factory strips added to the GTS) address this somewhat.
A lot of other things such as door and hatch strips, side window adjustment, b-pillar foaming, wheel wheel liners, etc. can all make a difference. My '90 is now relatively quiet, but not to the standard of new cars - it's an old car afterall.
05-10-2016, 05:48 PM
#19
Rennlist Member
I did a lot of soundproofing on both of my 928's. On the 89GT I did it over several weeks while driving to and from work during the week. On the GTS I did most of it in one week. With both cars the biggest difference was doing the doors and the B-pillars. On both cars I removed the door panels and covered the entire door with dynamat, cutting slots (not holes) for the wiring and door handle rods. On the B-pillers, I removed the wheel well liners and sprayed expanding foam in the area. Then re-installed the liners. A good trick I used was to cover the liners at the B-piller area with scaran wrap, reinstall and then spray the foam thru the cracks and gaps where the liners meet the fender well. That way the foam doesn't stick to the liners.
I could never tell a difference doing the floors or the area behind the rear seats. I did it but I couldn't tell a difference.
I could never tell a difference doing the floors or the area behind the rear seats. I did it but I couldn't tell a difference.
05-10-2016, 08:57 PM
#20
Nordschleife Master
Different.
https://rennlist.com/forums/928-foru...38-a-pair.html
Also, I was running down the freeway a bit below 80 mph yesterday.
Quiet enough that I could hear my fingers tapping on the steering wheel.
https://rennlist.com/forums/928-foru...38-a-pair.html
Also, I was running down the freeway a bit below 80 mph yesterday.
Quiet enough that I could hear my fingers tapping on the steering wheel.
05-10-2016, 10:27 PM
#21
Rennlist Member
Jim: How are the GTS fender liners constructed?
If some sort of deadening material is adhesively attached, could similar material be added to regular liners? Could material be added to the inside of the wheel housings themselves? I suppose the noise reduction would not be dramatic, not worth a lot of effort, but if it were easy it might be worth trying.
In my car, it seems like most wind noise comes from the top of the windshield. I might be wrong; I should drive around with my mechanics stethoscope, or cover the area with masking tape.
If some sort of deadening material is adhesively attached, could similar material be added to regular liners? Could material be added to the inside of the wheel housings themselves? I suppose the noise reduction would not be dramatic, not worth a lot of effort, but if it were easy it might be worth trying.
In my car, it seems like most wind noise comes from the top of the windshield. I might be wrong; I should drive around with my mechanics stethoscope, or cover the area with masking tape.
There are no "regular" rear liners pre-91, but rather a hard plastic (ABS) shield ahead of the rear wheel, and for some years there was a shield behind the real wheel to protect the PSD pump (e.g. '90 and early 91 before the full liner).
Some folks have glued foam to the backside of the shield ahead of the rear wheel, others have packed or sprayed foam in that cavity. I worry about trapped moisture in the latter case.
Our road noise was clearly coming from the doors and aft, generated from the rear wheels (which, oddly, always seem to have the least tread and hence the most noise). So it is a tradeoff between Dynamat or similar on the rear-deck floor, doors, etc, or trying to kill it closer to the source.
05-10-2016, 10:32 PM
#22
Rennlist Member
Of course it is all relative to the roads, it would be fun to race crappy Texas chipseal against crappy Washington chipseal.
05-11-2016, 08:32 AM
#23
Three Wheelin'
I currently have my passengers seat out and noticed on the '85 that there isn't anything directly under the seats in terms of carpet or sound deadening material. Considering the exhaust is right underneath that location that might be a good location for some acoustic controlling material. I have some left over Dynomat kicking around the garage that I'm going to cover that area with and see if it deadens some of the X pipe drone.
05-11-2016, 08:49 AM
#24
Three Wheelin'
Somewhat back on topic...
It's funny that you say the Sumitomo HTR's are noisy, I had a set of Yokohama Advan Sports on the car for about 5 years and the road noise really transmitted in to the cabin. I changed out the rear wheel bearings thinking one was going bad and no change. Added foam in the b pillars and Dynomat behind the speakers, again no change. Last week I swapped out the Yoko's for Sumi HTR's and it made a huge difference in cabin noise. Acoustics are subjective
It's funny that you say the Sumitomo HTR's are noisy, I had a set of Yokohama Advan Sports on the car for about 5 years and the road noise really transmitted in to the cabin. I changed out the rear wheel bearings thinking one was going bad and no change. Added foam in the b pillars and Dynomat behind the speakers, again no change. Last week I swapped out the Yoko's for Sumi HTR's and it made a huge difference in cabin noise. Acoustics are subjective
05-11-2016, 06:02 PM
#26
Rennlist Member
I used felt batting that we use for airplane windshields under the ouuter trim.
It was a temp job, but it worked incredibly well. Esp if your trim was been removed and put back on, its not as flat to the glass as it used to be.