Downpipe Turbo Subaru FAQ
How do I install a downpipe? Refer to the downpipe manufacturer’s instructions. For downpipes without instructions, below are links to some of the better known downpipe installation instructions:
Keep in mind that the short black rubber hose on the passenger side side of your fire wall is the AC drain line. It’s best to ensure that it is routed away from your new downpipe to ensure it properly drains and does not melt onto your downpipe. It can drip onto your downpipe and this causes no reported problems if you choose to cut it short and allow it to drain on the downpipe itself. Though not the best route, this is mentioned as a possibility.
What about ceramic or other heat wrap coating? Though there are pros and cons to heat retention treatments with exhaust components, the general consensus with headers is that heat retention benefits outweigh the liabilities.
Pros:
Increased heat retention, which is beneficial for exhaust flow.
Reduces underhood temps, which decreases IC heatsoak.
Cons:
Additional expense.
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.
What types of ceramic or other heat wrap coating are available? The two most popular manufacturers of heat wrap are Thermo Tec and DEi. The two most popular coating manufacturers are Jet Hot and Swain Tech Coatings. Wrapping is a DIY project with a shorter life span than the professional only coating with a longer life span.
.pdf file on coatings
Car Craft magazine’s testing of Jet Hot
What is the CEL fix? It stops the rear CEL code P0420 Catalyst System Efficiency Below Threshold from appearing, this code being caused by the lack of a catalytic converter in the exhaust. ***NOTE*** There are two CEL fixes for the WRX, the other one is the 2.2K Ohm 1/2 watt resistor. It is used to combat the CEL code P0546 = Exhaust Gas Temperature Circuit Malfunction (High Input) in the uppipe. This notice, though not important to this thread, acknowledges there are two “CEL fixes” and defines them individually to avoid possible confusion.