Exhaust theory experts needed: quietening the evoTT!
^ gotcha. Heard about that QC issue.
I think I'm going to try the X muffler because it's relatively low cost and easy to implement. I don't think it'll do too much for the drone except make the entire exhaust quieter (I'd prefer only low rpms are quieter). But I'll take what I can get.
To get rid of a specific resonant frequency, I think I'm going to have either get a tuned resonator or muffler or put in a pipe of a specific length. Not much room in there for another 4 ft long pipe, or resonator for that matter...
Maybe I can get 2 of Motordynes VQ mufflers to replace the evoTT's barrells. If it'll fit...
I think I'm going to try the X muffler because it's relatively low cost and easy to implement. I don't think it'll do too much for the drone except make the entire exhaust quieter (I'd prefer only low rpms are quieter). But I'll take what I can get.
To get rid of a specific resonant frequency, I think I'm going to have either get a tuned resonator or muffler or put in a pipe of a specific length. Not much room in there for another 4 ft long pipe, or resonator for that matter...
Maybe I can get 2 of Motordynes VQ mufflers to replace the evoTT's barrells. If it'll fit...
I love the sound of the evoTT at WOT but long story short, I want to get rid of the drone from 1800-2500 rpms on the evoTT. I personally think it is worst at 2k rpms, city driving, so that's my primary target.
I was thinking of Tee-ing off a closed-ended 2" round pipe from the H-pipe on the evoTT. The goal here is to have a pressure wave that is exactly phase-shifted 1/2 the wavelength from the resonance that is occurring at 2k rpms.
So by my calculations, 2000 rpms, is 1000 exhaust pulses per minute * 6 cylinders = 6k pulses/min / 60 = 100 firings per second, divided over two banks for a dual exhaust. The wavelength for a 100 Hz audio signal at 400 degC (that's a guess for the temp at the H pipe in the evoTT) is 520 cm according to this link. So to generate a wavelength cancellation pulse, the pulse would travel to the end of the closed pipe and reflect back - so the pipe would have to be 1/4 the wavelength or 130 cm.
That's 4.2 feet! Are these calculations correct?
Tell me this - why doesn't a pulse from one bank cancel out the pulse from the other bank via the H pipe in the evoTT?
I would post a picture of the evoTT but I can't find a good one on the 'net. If anyone has a complete pic from back to front, can you post?
I was thinking of Tee-ing off a closed-ended 2" round pipe from the H-pipe on the evoTT. The goal here is to have a pressure wave that is exactly phase-shifted 1/2 the wavelength from the resonance that is occurring at 2k rpms.
So by my calculations, 2000 rpms, is 1000 exhaust pulses per minute * 6 cylinders = 6k pulses/min / 60 = 100 firings per second, divided over two banks for a dual exhaust. The wavelength for a 100 Hz audio signal at 400 degC (that's a guess for the temp at the H pipe in the evoTT) is 520 cm according to this link. So to generate a wavelength cancellation pulse, the pulse would travel to the end of the closed pipe and reflect back - so the pipe would have to be 1/4 the wavelength or 130 cm.
That's 4.2 feet! Are these calculations correct?
Tell me this - why doesn't a pulse from one bank cancel out the pulse from the other bank via the H pipe in the evoTT?
I would post a picture of the evoTT but I can't find a good one on the 'net. If anyone has a complete pic from back to front, can you post?
Without the right tools, designing a quarter wavelength resonator and getting the result you want from paper to the car, is going to require quite a bit of trial and error. Not to mention most quarter wavelength resonators are effective for a very narrow frequency range.
The easiest solution would simply be to increase muffler volume in the entire system, using whatever parts fit your needs.
TK
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