Joescoobs74

Trawling through various posts I have noticed that most modded STI's seem to ditch most parts of the exhaust system. I can understand how a decat/sportcat can give the car more power, but I don't see that replacing just the backbox of an STI with say a Hayward & Scott or a Prodrive one can offer a big improvement.

As an example if you were to get a TEK3 mapping done and kept the standard backbox would you notice any difference had you fitted an aftermarket exhaust (keeping the standard cats)?

I look forward to hearing your views on this?

Trashman

On its own perhaps 5-10bhp at absolute best. I think most change it first as the standard one is somewhat muted. Something like a Scoobysport lets it burble

AvalancheS8

Changing the downpipe for a de-cat one makes the biggest difference. On a U.K car with a cat in the centre section, changing this for a de-cat pipe makes the next biggest difference, on a car with no centre section cat (JDM Sti's etc) this is obviously already done. Changing the backbox makes the smallest difference power wise, particularly if the down and centre pipes are standard, but as stated above, it is usually done for the noise as much as anything. On an otherwise fully de-catted system I'd guess that the performance difference between standard and aftermarket backboxes would be greater than changing them on an otherwise standard system.

Joescoobs74

Thanks for the info guys, seems as though its purely a case of cranking up the volume on the flat four burble, for a standard system

scooby-k

prodrive performance upgrade (ppp) cahanges the back box and removes middle cat amongst other things so I think if you follow their idea you won't go far wrong
ken

Engineer@Uni

Don't forget that it'll be bad publicity if subaru offers a noisy car. Just because we love the burble doens tmean the motoring press (and consequently general public) will like a high-decibel engine note. Also, new cars are suspect to exceedingly tight emissions regulations. This is why subaru offers the PPP. As the PPP is sold after the vehicle, then the car doens't have to obey to such strict emissions. Effectively, the emissions from the better exhaust wouldn't qualift for a car to be sold from the factory, but does qualift as "road-worthy".
With just a remap, it would be doubtful if you were sane. 10-15 horse at most, I shoudl think. Plus, if you later changed the exhaust, you'd need another remap anyhow.