WRX Info

Frequently Asked Questions

Exhaust FAQ: Uppipe

The primary purpose of an aftermarket uppipe is to remove the catalytic converter housed within the stock unit. This serves two purposes: to increase horsepower and decrease turbo spool time.

HP gain is around 10HP. This figure is highly debated as different manufacturers use different dynos with different cars with different levels of mods. Dyno Proof Example. The general consensus for turbo spool time decrease is boost will occur around 500 RPM sooner.

Is an aftermarket uppipe a performance or reliability mod? With regard to swapping over from a catted uppipe to a catless uppipe, it's both. Need some evidence of the reliability? View this link.

Which manufacturer is best? This topic is highly debated. There have been no reported consistent "bad" uppipes on the market. Obviously, there may have been bad pipes sold, but not enough to report as "bad" overall.

What uppipe metal material is best? Uppipes are made from mild steel, stainless steel (304 & 321), cast iron, and inconel. There is no irrefutable evidence that one material is better than the other. Obviously, corrosion levels are higher with mild steel (coated or otherwise) and cast iron. Corrosion on cast iron, due to it's thickness and material qualities, is more resistant to corrosion damage than mild steel. In terms of heat retention, the best material is inconel. Article on exhaust materials.

Which uppipe construction method is best? Uppipes are either solid or flex. There is no irrefutable evidence that one design is better than the other. The thought process is that a flex pipe will reduce the chances of leaking. Practical application has shown that correct installation plays a bigger role than the uppipe construction.

What is the cheapest uppipe? Gut your stock uppipe. Instructions. Gutting your stock uppipe can have the same benefits as using a more expensive aftermarket uppipe. Dyno Proof.

Which uppipe has the best gains? There is no irrefutable evidence that any uppipe has better gains than another. The consensus, if there is one, is they are all within 1-2 HP, gain wise, of each other.

Where do I buy an uppipe? Every Subaru/Import performance store sells uppipes. For purchasing, support your local economy or the NASIOC Vendors.

Should I replace the uppipe in my STi or 06+ turbo Subaru? All STi and 06+ turbo Subaru models have a catless uppipe. The big difference is that that the STI or 06+ turbo Subaru went from 2.0 to 2.5 displacement. Buscher Racing (post 318 and on) proved that going to an aftermarket uppipe vs. OEM catless does show gains. Does this mean an uppipe should be thought of in the upgrade path for 2.5L Subarus? Though it was once thought no, now one should consider it.

Are WRX and STI uppipes the same size? Yes. You may swap WRX and STI uppipe of all years as they are the same size. Remember that 02-05 WRX uppipes have catalytic convertors, so it's not a good idea at all to install one of those on a 06+ WRX or STI, but they will fit.

How hard is it to install an uppipe? Allow around 5 hours for install time. This can depend on many variables. jaxscuby is the current world record holder at 1.25 hours! A lift and air tools will significantly speed up the process but aren't entirely necessary. Professional installation, depending on your area, is around $300. Shadetree mechanics will install for around $100. Friends and install parties via your local Subaru club run the cost of beer and food.

How do I install an uppipe? Refer to the uppipe manufacturer's instructions. For uppipes without instructions, many rely on the Vishnu instructions for installation. Below are links to some of the better known uppipe installation instructions:
Vishnu's Instructions
Perrin's instructions
Scoobymods.com's Instructions, with pictures (using Perrin's instructions)
TurboXS's instructions
Scoobymods.com's latest instructions
Installation VIDEO
Scoobymods.com instructions

What part numbers might I need for this install? For best results, replace all the gaskets that are used for an install. The top and bottom uppipe gaskets MUST be replaced! Actual part numbers are not listed due to frequent changes; consult your dealer or online retailer for ordering.

OEM part names and approximate retail prices:
$15 Cross pipe, Left side
$10 Uppipe Gasket (Bottom)
$10 Uppipe Gasket (Top)
$16 Downpipe Gasket (DP to turbo)
$7 Cross pipe, Right side
$12 Manifold Gasket to the block
$200 2.0L uppipe
$200 2.5L uppipe
$59 EGT sensor

Are there any other parts I might need? Occasionally, an uppipe (especially used ones) will come without uppipe studs. If you are unable to obtain them from your Vendor, you will need five of SOA part number 800910340 which retail for ~$8.50 each. Alternately, you could source an automotive stud, m10 x 1.25 by 41mm at a parts store, preferrably Grade 8. Removing studs from an OEM uppipe usually will end up ruining the studs. You do not want to start an uppipe install with the hope that you can remove the stock studs. For removal or installation of these studs, be sure to use the double nut method.

Is there any other gasket information? Some users enjoy the extra piece of mind that comes with different gasket solutions rather than relying on the OEM gaskets. Some users source 5 ply gaskets. These are made by the same manufacturer as the OEM 3 ply units, but are 2 plys thicker. Some users have doubled up on the OEM gasket. Some users source copper gaskets. Recently, Turn in Concepts worked in conjunction with Remflex to offer the first 100% graphite gaskets that look extremely promising. Additionally, many people have had great sucess using high heat copper gasket making substances applied to the top and bottom uppipe gaskets. These are marketed by various companies and brand names, but generally come in an orange package and contain copper as one of their main ingedients. Most of these advanced gasketing materials and products are generally used on the bottom uppipe gasket as there is the #1 source of uppipe leaks.

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.
Increased heat retention, which is beneficial for exhaust flow.
Reduces underhood temps, which decreases IC heatsoak.
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.

Car Craft magazine's testing of Jet Hot

Do I need an EGT bung? No. The EGT bung is there for one purpose. It houses the EGT probe that monitors the exhaust temperature so the engine heat does not break down the catalytic converter element if the EGT becomes too hot. Since your new uppipe has no cat, you don't need an EGT probe.

My uppipe has an EGT bung, should I plug it or reinstall the stock EGT sensor? There is a chance down the road that EGT probe could burn up and pieces of it could be ingested by the turbo. Plugging it is the best option. You will need a M12x1.25 bolt. They can be tricky to find and many go to auto parts stores and ask for this type of oil drain bolt. True hardware stores are also a good place to find these. You may consider a jam nut if the bolt is too long, or you could trim it down to fit better. High temp thread locking compound is also an option.

What is the CEL fix? 2.2K Ohm 1/2 watt resistor. These are available at Radio Shack and are usually in stock. $1 buys you 6 of them. You place it in the EGT connector, which is the bottom connector just forward of your passenger side strut tower. It only has two holes, so jam one end of the resistor into each. If you do not use this resistor, you will probably end up with the CEL code P0546 = Exhaust Gas Temperature Sensor Circuit Malfunction (High Input). ***NOTE***There are two CEL fixes for the WRX, the other one is the rear CEL code P0420 Catalyst System Efficiency Below Threshold, this code being caused by the lack of a catalytic converter in the downpipe. This is usually fixed with an electrical fix or mechanical fix. This notice, though not important to this thread, acknowledges there are two "CEL fixes" and defines them individually to avoid possible confusion.

Should I reset my ECU after this mod? It is never a bad idea to perform an ECU reset after a mod. The traditional route is to disconnect the negative battery terminal, press the brake pedal for a few seconds to bleed the system of charge, and reattach. Some use the more advanced Vishnu Reset.

What about emissions problems like emissions tests and legality? The main purpose of the uppipe cat is to keep cold start emissions low until the main catalytic converters warm up. Using a catless uppipe is a violatation of section 203 of the Clean Air Act. Each state has statutes that cover this subject as well. There have been no know reported cases of catless uppipes causing state emissions test failures.