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750HP, 130 dB(A)!? Can you hear me yet!
Check to see if the regulation is 90dB or 90dB(A), some EU countries use dB(C) for pass by regulations. The A scale is closest to human hearing which weights each frequency accordingly, with 1000Hz being the most heavily weighted and tapers off above and below 1KHz. dB with no weighting has even weight across the freq. spectrum, and our engines are spiking frequencies from 10Hz to 250Hz giving the potentially deafening dB values being posted. In A scale, your 130dB is probably more like 108dB(A), and 112dB(C). Also, distance from the car and location in relation to the sidepipe is very important. A couple of feet could change a couple dB, and move forward of the exhaust exit as much as regulation allows. Microphone direction and equipment calibration is also a factor. Unless you are using a very good sound pressure level meter, error can easily be 5dB. There are decibel conversions for scales calculations available on the web. We were recently looking into building a car for a Swiss customer, which has an 80dB(A) regulation, and determined its virtually impossible to meet with cats and sidepipes
Hope this helps.
Jay
Classics by Elite LLC.