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I have stock manifolds and the "dreaded OBX cat back" system. LT, auto, 259's. It drones some at the lower cruise R's when I roll my foot into it heading up a grade in OD.
I did the sound deadening mat this weekend when I put in the rear carpet kit. Helped tremendously.
Can you go into the word "tremendously" a little more and reveal your source for the mat? How heavy is it?
I used to have really bad drone, so much that the wife and I woukd wear ear plugs on the highway.
When it came time to redo my exhaust I did true dual 2.5 pipes from the headers back (no cats) with an X-pipe and Corvette Central's No drone dual outlet mufflers. Worked like a charm, no drone but still a moderatly agressive sound.
After I removed the carpet and pad, I tapped on the floor pan. It's like a hard plastic bass drum. I can see why there's some sound issues.
Don't forget about the hidden locking compartment under the carpet in the cargo area. There's a hollow area with a plastic vibrating storage tray in there above the tire jack. I just removed the tray and stuffed an old bath towel inside the opening. It appeared this loose plastic tray in a hollow area could possibly collect exhaust noise from underneath and multiply it. I'll soon find out if it made any difference in drone sound.
I'm hoping Dynamat xTreme on almost every square inch of my '87 C4 will help drone and general road noise. With a simple knuckle knock test the hollow fiberglass rattle is now more of a light thud. The rear storage area is probably the thinnest area and largest offender, which also happens to sit partially above the mufflers. Since these pictures were taken I've done most of the driver area though I'm leaving the bell housing and shifter area to do after a ZF6 swap since we'll have to cut the trans tunnel a little. I also need to do the doors. I'm also going to add Dyanaliner to the drivetrain/exhaust area to hopefully help limit some heat.
I'm hoping Dynamat xTreme on almost every square inch of my '87 C4 will help drone and general road noise. With a simple knuckle knock test the hollow fiberglass rattle is now more of a light thud. The rear storage area is probably the thinnest area and largest offender, which also happens to sit partially above the mufflers. Since these pictures were taken I've done most of the driver area though I'm leaving the bell housing and shifter area to do after a ZF6 swap since we'll have to cut the trans tunnel a little. I also need to do the doors. I'm also going to add Dyanaliner to the drivetrain/exhaust area to hopefully help limit some heat.
Based on my experience with this product this is a 'better' option but substantially more expensive than the other posted here.
Based on my experience with this product this is a 'better' option but substantially more expensive than the other posted here.
I bought the mega pack from Amazon for ~$300. It came with nine 24"x48" sheets of Dynamat xTreme which works out to 72 sq. ft.. It looks like the one package is going to cover everything except the doors. Had I not done the storage passenger bin and the ABS pump/computer area it may have done the doors but it would be close. I've been doing my best to cut out sections to reduce waste as much as possible and then use small random cutoffs when I find small areas that need a little touching up. I've also gone through two rolls of Dynamat tape but it isn't really necessary if you want to skip using it. I'll probably go through 1-2 more from the looks of it, they go for ~$19 for two rolls. I haven't yet measured how much Dynaliner I want to buy.
My exhaust system has seen a few changes over the years. When I first got the car I had the OBX longtubes and a 3" magnaflow catback with LT1 tips. This system droned quite a lot. So then I got the 2.5" OBX catback, which killed quite a bit of the drone. It was nice to drive after that BUT the system killed alot of the sound so I decided on Corvette central muffler deletes w/ LT1 tips while still using the OBX resonators and it sounds great; has some volume and does not drone in my cruising rpm. So I'm very happy with the system I have now.
If I couldn't beat the drone I was planning on doing the helmholtz resonator idea. The vast majority of skeptical people who have done it have been blown away by how well it cut drone. I've seen happy people from small 4 banger cars to big V8 cars. It basically bounces back certain frequencies into the exhaust to cancel the drone frequency. If you don't know what it is look it up. It has been tested by lots of people and it works.
Not to discourage anyone who is doing the dynamat, because it does help, but drone still penetrates through.
The drone on my car is ridiculous, but i love the way it sounds so much at 6000 RPM that i live with it.
I did the 80mil Noico throughout the entire car, and then did a layer of frost king for thermal insulation on top of it. It did deaden down a lot of sound, but if you have drone like I do, it doesn't eliminate it. My next step is to build 1/4 wave resonators under the car and kill my drone frequency that way.
Last edited by Pwnage1337; 08-16-2018 at 01:13 AM.
My exhaust system has seen a few changes over the years. When I first got the car I had the OBX longtubes and a 3" magnaflow catback with LT1 tips. This system droned quite a lot. So then I got the 2.5" OBX catback, which killed quite a bit of the drone. It was nice to drive after that BUT the system killed alot of the sound so I decided on Corvette central muffler deletes w/ LT1 tips while still using the OBX resonators and it sounds great; has some volume and does not drone in my cruising rpm. So I'm very happy with the system I have now.
If I couldn't beat the drone I was planning on doing the helmholtz resonator idea. The vast majority of skeptical people who have done it have been blown away by how well it cut drone. I've seen happy people from small 4 banger cars to big V8 cars. It basically bounces back certain frequencies into the exhaust to cancel the drone frequency. If you don't know what it is look it up. It has been tested by lots of people and it works.
Interesting. the obx "resonators" look like two "cherry bombs".
The thing about straight through "mufflers" without chambers or a forced route of some sort is they get louder and louder and louder as they build up soot.
I think this is the case with any muffler to a lesser extent when force routed.
You must be pretty young if you are able to deal with that drone.. I did that **** when I was in my 30's.. two cherry bombs on a 88 bmw M3... holy cow!
That being said I really want my vette to sound "cool"... I'll reach nirvana one day. Right now my biggest beef with the LT1 is it doesnt have distinct firing.. its all mixed up.. I dont know if the cats are doing that or in my case the stock resonator or what.. but, while one might refer to it as a "european" sound I just want a good ole american v8 sound. I think its gonna take a cam and headers but who knows. Every single thing Id like to do to my car is expensive. ugh
Interesting. the obx "resonators" look like two "cherry bombs".
The thing about straight through "mufflers" without chambers or a forced route of some sort is they get louder and louder and louder as they build up soot.
I think this is the case with any muffler to a lesser extent when force routed.
You must be pretty young if you are able to deal with that drone.. I did that **** when I was in my 30's.. two cherry bombs on a 88 bmw M3... holy cow!
That being said I really want my vette to sound "cool"... I'll reach nirvana one day. Right now my biggest beef with the LT1 is it doesnt have distinct firing.. its all mixed up.. I dont know if the cats are doing that or in my case the stock resonator or what.. but, while one might refer to it as a "european" sound I just want a good ole american v8 sound. I think its gonna take a cam and headers but who knows. Every single thing Id like to do to my car is expensive. ugh
Stock exhaust routing is 2-1-2 it is similar to an X pipe installation = European sound.
Small block firing is all the same.
Suggest true duals for that V8 sound, an H pipe helps a bit with low rpm torque however benefits diminish as rpm increases.
Interesting. the obx "resonators" look like two "cherry bombs".
The thing about straight through "mufflers" without chambers or a forced route of some sort is they get louder and louder and louder as they build up soot.
I think this is the case with any muffler to a lesser extent when force routed.
You must be pretty young if you are able to deal with that drone.. I did that **** when I was in my 30's.. two cherry bombs on a 88 bmw M3... holy cow!
That being said I really want my vette to sound "cool"... I'll reach nirvana one day. Right now my biggest beef with the LT1 is it doesnt have distinct firing.. its all mixed up.. I dont know if the cats are doing that or in my case the stock resonator or what.. but, while one might refer to it as a "european" sound I just want a good ole american v8 sound. I think its gonna take a cam and headers but who knows. Every single thing Id like to do to my car is expensive. ugh
I'm 28 but I was done with the horrid noise around 25. The exhaust now really is quite tame but nice and LOUD at WOT. I putt through town and then drive more aggressively once I'm out of town. The drone NOW is basically non existent compared to the Magnaflow or the OBX. Just yesterday I was driving it and there is no drone in the cruising rpms. Sure it's loud but the overall volume is behind the car, the drone is what makes a car unbearable inside the cabin. Yea the resonators basically are just glasspacks/cherrybombs but apparently they do their job. I took off the OBX mufflers and ran the car without mufflers when I was in the process of putting on the deletes and it was still almost just as quiet. It sounds MUCH better now too.
Drone is function of the system components. Laying down sound deadners/mats doesn't fix the problem it only masks it. Kind of like wearing ear muffs, they do nothing to change the source of the sound.
I hade 40 series Flowmasters on my '94, it was fun and cool for all of 5 minutes. Took those off and installed Walker Dynomax mufflers and all was good.
Drone is function of the system components. Laying down sound deadners/mats doesn't fix the problem it only masks it. Kind of like wearing ear muffs, they do nothing to change the source of the sound.
I hade 40 series Flowmasters on my '94, it was fun and cool for all of 5 minutes. Took those off and installed Walker Dynomax mufflers and all was good.
Thank you sir
Hence why even though I don't have mufflers I don't have drone issues in my cruising rpm. Changing the exhaust layout moved the resonance frequency higher or lower than my cruising rpm.
I'm more curious in the cause of C4 drone. I have extensive wheel time in C2 Corvettes and they don't drone despite having a glass enclosure behind the driver. I've driven C3s and most don't drone. What is it about the C4 that causes drone? All the earlier generations mentioned have mufflers in similar locations which rules that out. I'm aware of exactly what drone is, but specific causes in the C4 puzzle me (especially since it doesn't appear to affect earlier cars. Thoughts about the science behind it welcome, not looking for a brand shootout. Thanks for any insight into this.
My California model 1996 LT1's former loud droning exhaust set-up was as follows: Stock exhaust manifolds leading into two stock cats (one on each side) then into the single stock resonator, then leading into a pair of Magnaflows that had a slightly larger pipe leading into each of them. This set-up caused a loud cabin drone when accelerating, especially on an incline...OMG. Sounded great on the exterior, but irritating on the interior.
I just had a Magnaflow #12468 (a kind of resonator/muffler with an internal X-pipe design) installed replacing my stock resonator. Same basic size as the stock one with dual 2.5" inlet/outlets. It won't easily bolt on without a lot of fabricating of pipes/fittings, so use a pro muffler shop, unless you're a welder. I had a pro muffler shop weld the new resonator into place. Now The Big Discovery: This new Magnaflow resonator has the x-pipe design, BUT the old stock resonator had a straight through design of two separate perforated pipes traveling through the housing and never completely mixing or crossing the exhaust flow. The x-pipe mixing design of the Magnaflow resonator lowered the original loud drone of my rear Magnaflow mufflers. I was able to obtain a noticeable decrease in drone! I'd estimate it decreased by 20% to 30% even on the dreaded accelerating inclines. No codes or warning lights tripped either. I'm hoping I created a tiny bit more performance exhaust flow with the internal x-pipe design of the new Magnaflow resonator. Therefore, for anyone out there with a stock '96 LT1 exhaust or similar that wants a more aggressive exhaust note with very little drone...this Magnaflow set-up could be it. I was told my rear Magnaflows (polished stainless steel) cost the previous owner approx $400 for the pair. The Magnaflow resonator cost me $105 on Ebay. Even with pro installation charges, this is still waaay cheaper than a Corsa system, however with just a bit of livable drone.
I have a Corvette Central cat-back system on my '84, that's intended for the '85 (straight tips). On first installation, I had drone. This system is a single 3" dia, pipe from the cat that splits into four muffler outlets. The area of the four outlets exceeds to area of the 3" pipe! I tried reducing the area of only one of the four outlet tips a little bit, and viola!! No drone, and a nice tone!!
This is really interesting to me. Thanks for sharing. How long is the tip length that you reduced in size and what are the tip diameters of your setup?
Last edited by USAsOnlyWay; 08-16-2018 at 09:24 PM.
Drone is function of the system components. Laying down sound deadners/mats doesn't fix the problem it only masks it. Kind of like wearing ear muffs, they do nothing to change the source of the sound.
I have no expectations the sound deadening material will axtually fix any drone. My main goal was road noise, general C4 rattles, and if it cuts back some of the resonating volume it is a bonus.
This is why I programmed my transmission to to shift into overdrive until 70. I have straight through mufflers and really dont have much drone even in overdrive. I have the friggen 2:59 rear end so thats why 70mph. Cant wait to get a nice rear end.
how did you program the over drive? Is that a chip?
08-13-2018, 11:00 AM
Thank you sir
This system is a single 3" dia, pipe from the cat that splits into four muffler outlets. The area of the four outlets exceeds to area of the 3" pipe! I tried reducing the area of only one of the four outlet tips a little bit, and viola!! No drone, and a nice tone!!
