Quote:
Originally Posted by USStrongman
What in your opinion causes the drone in TRD exhaust? My assumption is it has more to do with vacuum created at the rear of the vehicle in a very square, non-aero design than actual exhaust causing it? To me, its creating a positive resonance in a vacuum and it bounces between positive and negative vacuums at speed. Kinda like leaving a rear window down and getting up to speed and the audible drone that happens inside the cabin. Unequal pressures from inside vs outside.
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The problem is the resonance the TRD muffler creates and it's impact on the big boxy cabin above it.
The TRD exhaust has an incorporated helmholtz resonator design which is specifically designed to kill drone. Just forward of the muffler, the exhaust pipe splits into two pipes that enter the muffler can. The stock muffler only has one pipe entering the muffler (which is also larger in size). Using my endoscope, I saw that one pipe has perforations as goes through the muffler can and out to the exhaust pipe. The perforations allow exhaust to get muffled within the packing of the muffler can. The other pipe goes straight through the muffler can and has no perforations what so ever and dead ends with a capped pipe that exits about 1.5" at the back of the muffler can.
I have debated about cutting that cap and lengthening the pipe another 5" to 6" to see if I can reduce the drone as helmholtz resonators are very dependent on the correct pipe length to cancel out the resonance wave. I don't think Toyota went far enough with their pipe length design to reduce the drone.