bro-fellow-old-man-Veloc (
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The midbox generally is there to just silent the exhaust. The Caucasians call it the 'resonator'. Generally it's recommended to maintain the piping size and get a straight flow design and generally the bigger the midbox the quieter your exhaust. If you have a look at Magnaflows website, they have a type of straight flow exhaust 'box' that doesn't slow down the flow of exhaust but quietens the exhaust at the same time. In fact it somehow speeds up the flow of exhaust. But since you have a S-flow muffler at the end, just get the straight flow with the largest size canister your car can fit without downsizing the piping size. If you're gonna swap to 2.3" then suggest you add the resonator only after you change to 2.3" throughout the setup. Generally speaking though. 0.2" difference shouldn't make too much of a difference I think?
Those twisters or whatever add a lot of back pressure to the setup. You already have a S-Flow and yours is a manual, so don't get those bullets or whatever. Don't waste your money.
Personally, without knowing what type of s-flow you're using (baffled or mandrel twisted or recirculated or just 90 degree bends) I'm going to assume ideal s-flow. Usually the biggest impacting parts of your exhaust is the headers, catcon and rear muffler. Get a decent 4-1 extractor and heat shield it or titanium wrap it (fibreglass is hard to work with) or ceramic coat it, get a high flow catcon (save the planet mah) and fit a good fitting sized pipe mandrel bent throughout. A large middle resonator (straight flow) and a decent s-flow muffler should by right give you a decent rumble but without the drone at higher revs. My old Wiras setup was like that. Idle had that pretty nice rumble and acceleration had a loud rumble then it went quiet when cruising at 3.5k rpm. Was somewhat louder when redlining but then again what doesn't make noise at those sort of rpms?
Ideally though, you'd probably do well to pay hard money to get a professional to properly calculate the length of exhaust, diameter, type of extractor, etc. I haven't seen any shop do these sort of calculations and have only ever seen it done in race cars.