I've never really heard what it is. Just muffler X drones more than muffler Y. How does pipe size, loading, compression, cam or anything else come into play and why is it always around 2,000 rpms?
This also applies to the cars body panels as that act like a drum and amplify the sound that is why the tarpaper sound deadener works.BornInAFord said:Muffler drone often is a result of the design of the baffles within the muffler, and the resulting harmonics rather than the size of pipes or whether one has an x or h or y or o pipe or headers. The sound pulses (waves) from each cylinder's exhaust valve burst have a certain frequency that increases as the RPMs increase. At a certain RPM, the muffler enhances these frequencies much like a guitar case, shape, and opening will enhance the sound of the strings' frequencies. This phenomenon is called resonance, and can be annoying when using certain muffler systems. Many popular two and three chambered mufflers have some sort of resonance frequency, although many aren't noticeable because the frequency is either canceled by other baffles within the muffler or is at too low or high of an RPM to be obvious. Some, like the Flowmaster 40s and 50s (2 and 3 chamber mufflers) have a reputation for droning because their resonance frequency is around 2000RPM, which is the RPM at which many cars will cruise.
Make sense?
Daniel
jes72mustang said:Good explaination, Thanks. I took my wife out in the mustang on Saturday and she was complaining about the drone. I have Flowmaster series 40s. What would be a good alternative when I do the new exhaust over the winter?
S-Car-Go said:Good explanation but I still think there's more to it. Most mufflers drone at ~2,000 rpms. This is usually in the cruise range of the average car. Why would muffler companies design something with a resonant frequency right at the typical cruise RPM? That would be like designing a motor that was efficient except at 65-75 mph.. I just put in an entire exhaust system, headers to tailpipes. It has a noticeable drone when I'm by myself, but will blow your ears out if other people are in the car (more weight). I used Dynomax Super Turbos which supposedly don't drone. I put borla's on my 94 and they didn't drone anywhere near the Dynomax. I'm very disappointed to say the least. If this was a vette, new Shelby, viper, etc, the drone would kill sales, so why should we settle? Those cars have free flowing exhaust w/o the drone and can make more than 400 hp. I'd like to do the same (I'm building a 350 hp 289). Any ideas how to lose the drone without swapping mufflers trial and error?
thx,
Derek
Not exactly the same since you have a vert. But I had a 3in X-pipe with turbo mufflers from dyno max. Drone wasn't that bad. But I went turbo, and have NO drone now.S-Car-Go said:Oh yeah, I love Xpipes but there was no way it would fit under here.
The drone/resonance has to do with the length of the pipe and its relationship to the length of the sound waves generated by the engine. I don't have the time to do the math, but I think if you do you will see that for about 2,000 rpm the length of the sound waves are about the same as the length of the tailpipe.mustangdave said:The answer to the problem is under most 80's Mustangs with factory exhaust. Stock mufflers had the same problem so Ford shortened the pipe on one side so that the mufflers were offset--no more drone!!!!!! Nothing to do with muffler or engine design...it just is.
After installing an aftermarket kit on an 86 the drone was there due to equal length pipes to the mufflers: I had the muffler shop cut one shorter and weld in a new piece and the drone was gone.
mustangdave said:The answer to the problem is under most 80's Mustangs with factory exhaust. Stock mufflers had the same problem so Ford shortened the pipe on one side so that the mufflers were offset--no more drone!!!!!! Nothing to do with muffler or engine design...it just is.
After installing an aftermarket kit on an 86 the drone was there due to equal length pipes to the mufflers: I had the muffler shop cut one shorter and weld in a new piece and the drone was gone.