Attention: TDR Forum Junkies I’m fairly new to CTD pickups and in the short time I’ve had mine have become totally impressed with the power, handling, driveability and pullability. I’m surprised, though, that Dodge didn’t do a better job of noise isolation. Maybe they began putting all their pennies in the HPCR ISB years ago at the expense of improving the Noise/Vibration/Harshness of earlier generation trucks. Don’t get me wrong; I do appreciate and enjoy the sound of my CTD, but have thought for some time it would be nice to take the hard edge off the Cummins “character”.
I’ve noticed in many threads the numerous approaches members have taken in reducing interior noise levels. I’ve borrowed some of those ideas and created a few of my own with reasonably good success and thought I’d share…. .
THE MODS:
1. Using “3M 90” spray adhesive, bonded “Barymat BM-1C” noise barrier composite sheet to the rear wall of the cab from window sill down to the floor. The sheeting is 1. 6 lb/sq ft noise barrier prebonded to ¼” open cell foam. Try www.blachford.com for info.
2. After removing all necessary interior components, I applied 3/8” thick open cell polyester urethane foam over the entire floor pan. Then I applied 3 longitudinal strips, 27” wide each, of “Barymat 5B-OD” noise barrier sheet overlapped at the two joints. I cut and trimmed the sheeting to conform to the floor contours and then used an electric heat gun to soften the material and allow it to conform to some of the more difficult contours. I understand that to reduce transmission of low frequency noise, a barrier with substantial mass is required. Lead was a common material in the past but has fallen into disuse because of the possible health effects. Blachford and other manufacturers offer safe, synthetic materials that provide similar performance. I also learned it’s important to “decouple” the barrier from the floor pan with something like an open cell foam. It allows the barrier to “float” and not vibrate in tandem with the floor pan.
3. To the back of the firewall on the drivers side, I applied the BM-1C composite sheet wherever possible.
4. Believing that a lot of the engine noise was coming at me from the firewall along the steering column where it penetrates the instrument panel, I installed alternating layers of BM-1C and 1 inch thick open cell foam behind the knee bolster panel. I carefully fitted the sheets for a good fit against the column making sure to leave room for the gear position indicator lever and cable.
5. Because of the difficulty in applying a continuous barrier to the upper half of the firewall, whether inside or out, I thought there’d be benefit in installing a horizontal closure panel below the instrument panel, to “seal in” any engine noise transmitting through the firewall. I used ¼” thick ABS plastic sheet and created the minimum openings for the foot pedal levers. I also bonded 1 inch thick open cell foam to the top side of the sheet and to as many of the flat surfaces within the instrument panel enclosure to help absorb and prevent reverberation and amplification of noise.
THE RESULTS:
---NOT BAD!!!---
1. I haven’t had much luck attaching my results data to this post. But I’d be glad to Email them to you. For both cold and warm engine, the sound level while loaded at 1750 rpm or mildly accelerating dropped about 4 dB. That’s a reduction of about 60% in sound pressure level and is quite noticeable to me and my gal. This result was of the most interest to me because the noise source here was engine primarily since the vehicle speed was zero or quite slow and therefore no road noise contributing.
2. At 100 kmh (62 mph), the noise level dropped about 2. 0 dB from 71. 8 to 69. 8. That may not seem like much at first glance, but you’ll notice the maximum possible reduction is just 5. 0 dB because of the road noise present at the same speed while coasting at no load (66. 8 dB). I think reducing 2. 0 dB out of a possible 5. 0 dB is decent and noticeable because of the major reduction in the engine noise component (60%). What you hear at 100 kmh is a combination of road and wind noise and a much reduced level of engine noise. Normal conversation levels are now possible and the stereo can be heard at lower volume settings.
3. Warm idle in my truck is now 57. 3 dB as compared to about 57 dB for the HPCR engine as per page 49 of issue 38. I’ve driven a 2003 and observe that my 2002 is still louder while accelerating and cruising, but that’s actually my preference. I’d be disappointed to spend k$50 on a diesel truck and have virtually all the diesel character engineered out of it!
MORE MODS?
I don’t think so. I think the sound level now is about the right balance between comfort and ruggedness. I might later consider some of the off the shelf engine shields but have reservations about increased engine operating temperatures. Sound insulators unfortunately are also good thermal insulators. I see potential problems with premature engine oil oxidation and possible reduced engine life. But then again, from what I’ve read, the ISB is quite tolerant of most of the modifications we inflict upon them!
Hope this information is of some benefit to you.
I’ve noticed in many threads the numerous approaches members have taken in reducing interior noise levels. I’ve borrowed some of those ideas and created a few of my own with reasonably good success and thought I’d share…. .
THE MODS:
1. Using “3M 90” spray adhesive, bonded “Barymat BM-1C” noise barrier composite sheet to the rear wall of the cab from window sill down to the floor. The sheeting is 1. 6 lb/sq ft noise barrier prebonded to ¼” open cell foam. Try www.blachford.com for info.
2. After removing all necessary interior components, I applied 3/8” thick open cell polyester urethane foam over the entire floor pan. Then I applied 3 longitudinal strips, 27” wide each, of “Barymat 5B-OD” noise barrier sheet overlapped at the two joints. I cut and trimmed the sheeting to conform to the floor contours and then used an electric heat gun to soften the material and allow it to conform to some of the more difficult contours. I understand that to reduce transmission of low frequency noise, a barrier with substantial mass is required. Lead was a common material in the past but has fallen into disuse because of the possible health effects. Blachford and other manufacturers offer safe, synthetic materials that provide similar performance. I also learned it’s important to “decouple” the barrier from the floor pan with something like an open cell foam. It allows the barrier to “float” and not vibrate in tandem with the floor pan.
3. To the back of the firewall on the drivers side, I applied the BM-1C composite sheet wherever possible.
4. Believing that a lot of the engine noise was coming at me from the firewall along the steering column where it penetrates the instrument panel, I installed alternating layers of BM-1C and 1 inch thick open cell foam behind the knee bolster panel. I carefully fitted the sheets for a good fit against the column making sure to leave room for the gear position indicator lever and cable.
5. Because of the difficulty in applying a continuous barrier to the upper half of the firewall, whether inside or out, I thought there’d be benefit in installing a horizontal closure panel below the instrument panel, to “seal in” any engine noise transmitting through the firewall. I used ¼” thick ABS plastic sheet and created the minimum openings for the foot pedal levers. I also bonded 1 inch thick open cell foam to the top side of the sheet and to as many of the flat surfaces within the instrument panel enclosure to help absorb and prevent reverberation and amplification of noise.
THE RESULTS:
---NOT BAD!!!---
1. I haven’t had much luck attaching my results data to this post. But I’d be glad to Email them to you. For both cold and warm engine, the sound level while loaded at 1750 rpm or mildly accelerating dropped about 4 dB. That’s a reduction of about 60% in sound pressure level and is quite noticeable to me and my gal. This result was of the most interest to me because the noise source here was engine primarily since the vehicle speed was zero or quite slow and therefore no road noise contributing.
2. At 100 kmh (62 mph), the noise level dropped about 2. 0 dB from 71. 8 to 69. 8. That may not seem like much at first glance, but you’ll notice the maximum possible reduction is just 5. 0 dB because of the road noise present at the same speed while coasting at no load (66. 8 dB). I think reducing 2. 0 dB out of a possible 5. 0 dB is decent and noticeable because of the major reduction in the engine noise component (60%). What you hear at 100 kmh is a combination of road and wind noise and a much reduced level of engine noise. Normal conversation levels are now possible and the stereo can be heard at lower volume settings.
3. Warm idle in my truck is now 57. 3 dB as compared to about 57 dB for the HPCR engine as per page 49 of issue 38. I’ve driven a 2003 and observe that my 2002 is still louder while accelerating and cruising, but that’s actually my preference. I’d be disappointed to spend k$50 on a diesel truck and have virtually all the diesel character engineered out of it!
MORE MODS?
I don’t think so. I think the sound level now is about the right balance between comfort and ruggedness. I might later consider some of the off the shelf engine shields but have reservations about increased engine operating temperatures. Sound insulators unfortunately are also good thermal insulators. I see potential problems with premature engine oil oxidation and possible reduced engine life. But then again, from what I’ve read, the ISB is quite tolerant of most of the modifications we inflict upon them!
Hope this information is of some benefit to you.
