Thanks! If I do decide to go with a downpipe mod should I hold off on the catback exhaust I'm planning to put in and do a full turboback instead?
I read somewhere that having a splitter between the wastegate and turbo exhaust outlet on the downpipe (see attached image) can improve throttle response do you have any experience with this?
Also I'd like to keep the car fairly quiet as it is my daily and I do a decent amount of highway driving, would installing a different down pipe affect that?
Great questions.
One person's "too loud" is another person's "too quiet" so this is a tricky area.
Based on evidence and trusted opinion I've come across, the critical area is just after the turbo. The tightness or openness of the exhaust further downstream has a much smaller effect on performance (but quite an effect on noise).
As such, one option for you would be to get a bellmouth dump pipe & high flow cat upstream section, then connect it with a smooth transition to the stock rear section.
If noise and budget are less of an issue, go for the full aftermarket exhaust system from a brand you trust (or have researched) to be the noise/look/quality/price you like.
Personally (on my SH Forester XT) I run an Xforce bellmouth dump pipe (no splitter) & high flow cat upstream section, then a custom mild steel mid and rear section with two resonators in line then twin "tri flow" mufflers. It's quiet by aftermarket Subaru standards but sporty by "normal car" standards. It's not a solution for everyone. Occasionally I wish I hadn't sold-off the X-Force rear section.
“Whatever happened to the Popular Front, Reg?” “He's over there"SPLITTER!The splitter option (or indeed the "divorced wastegate pipe" option) seems to be the subject of much internet debate. That on its own tells you that the issue isn't settled and the differences are either marginal or nonsense.
In the "pro splitter" camp, people say that the wastegate exhaust exiting next to the main turbine exhaust will somehow get in the way of that turbine flow and make the turbo sad.
In the "splitter suspicious" camp, people will recommend you look at the way the wastegate flap opens and how it interacts with the extra internal wall (which could be worse than no splitter).
Personally I would err on the side of "no splitter". If your best dump pipe option has a splitter then do your research about how the wastegate flap on your turbo opens (eg right into the internal wall?) to form a view on whether it's counterproductive.
Internet argument on splitters probably incoming in 3...2....1....
Other thoughts:(a) the wastegate is only open when the turbo is producing enough compressed air for the job at hand (needing to literally bleed-off excess exhaust energy under "wastegate open" conditions). Under such conditions are minute differences in post-turbo exhaust flow going to make a measurable difference? (as opposed to big differences like "stock dump pipe VS bell-mouth with 3" piping and big cat").
(b) As a rule, most people do (and few argue about) the stuff that is proven to work. Conversely, if internet heroes are arguing the toss on a modification making a difference (or not) it pays to research a bit harder and keep "bang for buck" in mind. Obviously do whatever aesthetic, fun or quality-of-life improvements you want, just don't get hung up on whether
Perrin or Cobb engine bay trims make the car faster.
(c) A lot of us car enthusiasts need to take a chill-pill and keep in perspective the differences between something that is the theoretical optimum for a
tight-rules track racing category where every 1% counts VERSUS a getting a bit more "go" out of a 1700+ kg AWD road car with full stereo, sunroof and leather seats on a reasonable budget for a bit of fun.
With item (c) I'm sort-of lecturing my younger self to not spend stress and worry on theoretical optimum stuff (at significant cost) when "pretty bloody good" will do just fine for a heavy daily-driven road car.
If either of us are ever running a formula open-wheeler race team we can go back to sweating the one-percenters. Or, do the one-percenters at home (for fun) where the only cost is your time.