funny you should mention hondas
i know a guy (here comes that yarn) with a b18 VTEC and everything he does to quieten it down kills the power
so as a result it freakin screams its butt off and goes like you wouldnt believe. BUT it attracts unwanted attention
backpressure? maybe what these guys had discovered was gas speed? get the exhaust going faster and it will suck out the last bit?
had a mini at one point too fun car

have a look at pro stock pipes those guys test and test and test. nothing goes on the car unless it works. they enclose their intakes in a box so noone can see them and hang covers over the sides of the motors while in the pits.
ive heard they even shorten the intake runners during a run as the rpms go up

so buy a flow bench and dyno, make 100 different sets of pipes, test em all and let us know how you went