Subaru WRX and STi Exhaust general info:
How hard is it to install an exhaust? Allow around one hour for install time. Professional installation, depending on your area, is around $75. This is one vehicle modification that is very simple and can be successfully accomplished by even the greenest shade tree mechanic.
How do I install an exhaust? Refer to the exhaust manufacturer’s instructions. I should eventually have a blog post about installing an exhaust.
Do I need aftermarket exhaust hangers? This can depend on many factors and the only clear indication is during the post installation driving test. Some exhausts work perfectly fine with the OEM hangers and some can benefit from the added stiffness or extended length of the aftermarket hangers provide. They are fairly inexpensive and can be good insurance for a perfect, rattle free exhaust install.
Increased heat retention, which is beneficial for exhaust flow.
Reduces underhood temps, which decreases IC heatsoak.
Additional lead time, in the case of coatings.
Increased heat retention, which in some cases, can accelerate metal fatigue, especially at weld joints.
No proven HP increase.
If you plan on using a coating, ensure you are aware of what impact this will have on your header warranty if applicable. Coating or wrapping your header can void exhaust component warranties. If using a ceramic-type coating, ensure it’s working heat range is above the known EGT. EGTs can be as high as 1400-1600 degrees in the extremes. Some normal coatings are not rated to this temperature level.