for an ek9? best will prob be mugen twin loop mate.2bh i personally dont think theres much difference in all the free flowing systems out there.you could get a custom one made up with no resonators so its a straight threw,would be very noisy but would have very little restriction.
I doubt the twinloop would give the best gains, I've heard a few people say they didn't like them in that respect - that they felt restrictive.
TBH, there will be very little between the power gains from different cat backs, but your best bet is to go with a good free flowing system. Have a read of blinx's thread:
I was planning on going de-cat. So the mugen twin loop isnt very good for power? What other reccomendations are there, as i have no idea when it comes to jap parts/maunufacturers as this is my first jap car.
Buddyclub Spec 2 is straight through free flow with no resinators and no boxes, makes best power but is very noisey, i sold two last week to members off here they should have them shorty so maybe they will put a post up?
out of the 3 ive used on my car which where fujitsubo RM01A, 5Zigen pro racer A spec and J's racing 60Rs i have to say that the J's was miles better than the other two in every aspect
best thing i think ive ever bought for the car
spoon N1 are said to be good also but are very loud
mugen twin loop is not a full 2 1/2 inch, it has a 2 1/4 inch section on the b-pipe which defeats the purpose of even having the rest in 2 1/2 inch. It also has a massive restriction when the gas is sent through two 180degree sections
Would be very interested to see results on a dyno though