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Quantum GP700
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Help required! I have added this thread hoping someone in the K community might have the time to do this recording for us.

For those of you who have not followed my thread I am using a Hytech twin loop muffler at present. For low speed its very quite and passes our road noise test in Australia which is very strict. On the track on full noise the car is LOUD. I guess this is a reflection of the HP being made and no turbo to muffle it down. 600WHP + 12% drivetrain losses + 85HP to drive the twin SC is a pretty big number! At the tracks I have run so far I have been ok as everyone loves the car, but Sandown is very strict and I want to have a go there next year so I will need to deal with this.

First we need to record the exhaust noise before any muffler from mid to maximum rpm's. Care must be made to ensure the mic and sound card have a good frequency response to pick up 2nd and 3rd harmonic. Most sound cards or usb sound adaptors can do this as long as you setup the recording options correctly. (bandwidth, recording format, etc.)

This recording is then run into a spectrum analyser to determine the noise versa frequency spectrum from the motor on full throttle. The 3" muffler can still be straight through, however we now add chambers which are at these resonant frequencies. This then creates an out of phase noise cancelling muffler which will sound different to the human ear, but to the noise meters it will be super quiet as these frequencies will not be present in the exhaust noise. The result will easily pass any track noise meter.

But this becomes a design project, and it would be good if the K20a community could joined forces with this. I am sure John at Hytech would make the mufflers for us.

Thanks in advance.
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Helmholtz resonator is the name of what you are looking to design, and there are plenty of equations available on the web to do what you are after.

There are a lot of variables involved in calculating the appropriate chamber size to target a specific frequency, which will require very precise testing & monitoring of the exhaust. Finding the proper frequencies to target will be one hurdle, but you will also need to determine the exhaust temp (at the point where the chamber will be) and the exhaust volume I believe.

Sounds like a great project, wish I knew more to help.
 
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