Ok well I suggest not messing with cat at all as emissions from v8 are really hi as it is, probably best to set a budget and get the best you can, just bare in mind that changing back pressure can alter how the engine performs and in extreme cases send ECU haywire. Probably best changing rear silencer for a quality stainless version with abit more note that way cat and pressure etc should remain ok.
Also some really picky mot testers may pull up an increase in noise as a fail but I've never known this happen.

Ok cheers for advice.

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