Exhaust Drone

[surypap3]

My TC has headers exhaust mod and the drone at 50 or 60 mph is deafening. Probably an aftermarket setup sold years ago and maybe still today. Any ideas?

[Clifton]

The less a muffler muffles, the more noise and drone at cruise. A small resonator will help a lot.  I have never run a single straight through muffler (Borla or Magnaflow) on an n/a engine without a small bullet style muffler first.

[surypap3]

Seems it would be a challenge to fit a resonator and a muffler. There might be a short strait section crossing under rear of the oil pan. That would really make a difference in the drone?

[jbcollier]

How about some photos of what you have?  How is it mounted and supported along the way?

[surypap3]

Included some photos of header, collector, intermediate pipe and muffler. The system is fastened at the engine exhaust ports, collector/intermediate pipe connection, intermediate pipe/muffler flange and at muffler rear to the transmission mount. There appears to be a welded section in the intermediate pipe. That's the strait area I thought maybe a resonator could be place if that makes sense. Header pipes 1.25" and intermediate 2.5" OD roughly.

[BDA]

That's pretty much the conventional setup. Some people put the muffler on top of the tranny crosswise and that might give you room for a resonator (IIRC, JB did something like that).

If you know what muffler you have, you can search CARiD.com for a quieter one. They sell a wide variety of mufflers and attempt to describe their relative sound. I have no idea how accurate their descriptions are, especially since, if they are tested, were probably tested on a Camaro or Mustang rather than a little four banger, but they are the only place that tries to quantify it so they may be the best we can do.

[surypap3]

If I have 6 to 8" in the intermediate pipe, Is that enough for a resonator to do some good?

[E Paul]

They look funny, but I stuck a SuperTrapp diffuser on my Seven to cut down the noise enough to not have to use earplugs or wear a helmet. Sound level can be changed by changing the number of disks. Of course this also affects the back pressure, but my "butt dyno" can't tell the difference.
https://supertrapp.com/supertrapp-444-2003-4-inch-universal-disc-only-muffler-2in-inlet

[BDA]

SuperTrapp is a great option. It gives a distinctive raspy tone.

[surypap3]

  They do look funny

[jbcollier]

The first thing is to make sure it isn't touching anywhere.  That's the most common source of noise.  After that, rev-ing it up at an idle should get it to make the drone.  Get it "droning" and use a stethoscope, or long screwdriver to the ear, to locate the source of the drone.

[surypap3]

OK. I'll give it a try

[Clifton]

Some mufflers aren't as good as others too. Straight through perforated core mufflers are louder and tend to drone compared to baffled style mufflers.  Is yours straight through or baffled type?  You could just have a loud muffler too. I know it's not a Flowmaster by the pic but they tend to be very loud. 2.5" in a straight through muffler would be a little loud in general. Vibrant makes a 12" resonator. I've used these on 3" to keep the drone down. Not a lot of room on a Lotus though.

[surypap3]

Do you suppose that since the muffler is clamped directly to the trans mount, without an insulator, that there is not enough isolation?

[jbcollier]

Usually it's good to bolt the exhaust directly to the engine/transaxle unit.  Introducing movement will also cause the exhaust to flex and possibly crack.  First see if you can narrow down a source for the noise first.  A rubber mount won't fix a loose baffle.