I found that the exhaust system on my car... it has invidia or something on the tip but Bee*R all underneath it on the mufflers (same co??) .. is quiet enough for the DB stationary test but seems to get significantly louder over 4,000....
Its heavy, has two normal style mufflers, I have installed a metal cat but it doesn't restrict flow..... oh and its 3.5 turbo back... Although the custom dump/front pipe has made it slightly louder again.... so Im prolly going to have to get retested just to check it still passes for the eng cert....
And my engine, manifolds etc are far from stock....
However the zeddles is as loud a mofo with the kakimoto exhaust but never ever gets pulled over... imported under the 15 year rule so has an engineering cert lodged against the rego.... guessing this might be the reason??? That or they have absolutely NFI what it is and just don't bother!!!
btw the test is conducted at 3/4 throttle of your designated redline for your vehicle.... ie where the redline starts on the standard dash.... they call it ESMP or engine speed at max power... so work that out and aim for something thats quiet around that rev range.... or shove a crap load of steel wool in the rear muffler... lol