downpipe question

[NixRX7]

I can understand the yank and UK versions of the RX7 needing a downpipe to get rid of the pre cat, but as the JDM ones dont have a pre cat what is the advantage of fitting a downpipe ? are the stock JDM ones restrictive ?
And how much louder do they make the car, mine is already decatted and has a huge straight thru silencer on the back and is LOUD already what difference would fitting a downpipe make

[ScuttleRX]

Yeah the aftermarket ones are larger than original, also a hell of a lot lighter too, well my one was at least.

I don\'t reckon you\'ll notice much difference noise wise with the mods you have already as they are the parts that do the most silencing if ya get what I mean.