I don't believe that insulating the trunk will eliminate ur drone. U might see some improvement, but I doubt u'll get satisfactory results. I have no X, H or crossover. I have longtube headers, don't know tailpipe size; I have semi-quiet mufflers "generic brand", w/ ex. tips out under the val/bumper. No drone --Can drive all day in comfort. Most of the system was there when I got the car - the only thing I changed was removing the Cherry Bomb, glass pack noise makers. Been happy every since.
I didn't think to add that I insulated my entire floor, even the trunk floor with the aluminum bubble wrap like stuff. But when I had the pipes dumping in front of the axle, I had a drone at about 40-45 MPH. Going over the axle and out the back killed that, but since yours already go out the back, that's no help to you. The insulation may help quite it a little, but probably not much. Do your pipes exit straight out or do they turn down? I've heard that pipes that turn down are louder due to the sound wave bouncing back up off of the pavement. Not an expert on that, but it does sound feasible.....
Decided not to do the AOD. Took some measurements and found that I'd have to have the exhaust pipes remade. And, a 28 ox 164 tooth flex plate was going to be hard to find or kind of expensive. Cost/benefit just wasn't right. Resold the AOD for what I paid for it. For details see http://mmb.maverick.to/showthread.php?t=82482 Rear axle is 3.00:1.
That's probably what Scooper was following up on with this thread http://mmb.maverick.to/showthread.php?t=76975 Interesting stuff. I'll look for the Mustang board info.
I'm also skeptical that insulation will be a fix. Probably have to add some glass packs in the tail pipes.
There are little turn downs bent into the ends of the tail pipes. Might help if they were straight out the back. Didn't want the pipes sticking out the back but may have to go that way.
Bingo, they will act like resonators. Just like the auto manufacturers use on OEM cars. On my mustang I have 40S flowmasters with 2.5" pipe and dynomax bullets as resonators. No drone what so ever at any rpm. And it's still loud and mean just not obnoxious. I had magnaflows before and they had a worse drone than the flowmasters.
Insulating shouldnt help with a true resonance issue. Its frequency your dealing with. It has to be changed to get rid of the resonance. The entire exhaust system factors into that. Its trial and error and some real involved math/science. Car companies spend millions designing exhausts etc. to eliminate frequency issues/ NVH noise,vibration,harshness. Spent 2 days on it a head office with our trainers. At least you know its the exhaust causing it. Thats the big battle and all the math work eliminated. Problem is what to change to get rid of it. The add on tubes at the tail pipes would work to cancel out the frequency but they take a fair bit of room which we dont have on these cars. The resonance on my car can really get to me at times also.
Interesting stuff. Yes, its definitely resonance. I can hear it at 1200-1300 RPM and then much louder around 2500. Harmonics, I guess.
Same as yours. Yes, I expect the muffler placement would affect it. Think the resonance might be standing waves either in the exhaust pipes or tail pipes. If the "Ts" in the tail pipes solve it I suppose they are in the tail pipes.
I stopped in a different custom muffler shop this morning to see what they might recommend. They weren't real positive about any solution. Owner is a great guy who, I think, didn't want to over promise and have a disappointed customer. But when I said I'd be satisfied with a 50%-80% reduction in drone, he opined that 12" glass packs as resonators would probably get at least a 50% reduction. He was right. I wasn't really expecting to get it done today -- so I didn't get before and after recordiings -- but he installed them while I waited. Drone is cut by 60%-70% I guess, which cuts the annoyance factor by a lot more than that. Wish it hadn't reduced the other "noise" so much but its fine. Probably not going to intimidate anyone at a light now. If I had to do the exhaust over again I'd take it to this shop, Henry's on Capitol Blvd in Raleigh.
