Re: Quiet -- stock like sound level -- turbo back exhaust
The HKS Legamax Premium and HKS Super Turbo Muffler are the quietest catback exhausts for the 2011+ STI. I've heard everything out there including Corsa, Cobb, ARK, Milltek, Grimmspeed, Maddad and the Q300 to name a few and they are all louder. The HKS systems have a Helmholtz Resonator in the middle for frequency tuning which is the main reason. The Super Turbo Muffler is actually quieter than the Legamax Premium because of the exhaust tips which kinda sucks because they look better. HKS muffler angle and tip arrangement is also perfect! Many other cbe systems have the mufflers & tips sitting in such a way they look as if they are pointing down.
The stock catback is fairly quite when attached to a properly fitted downpipe with HFC like Cobb. The HKS is louder than the stock exhaust when attached to the same downpipe and in all fairness it should be, but barely.
HKS is also releasing an anniversary edition full Titanium Super Turbo Muffler for anyone who wants to spend around $4k. Looks hot though!