The Part Most WRX STI Owners Overlook Until It’s Too Late
Most EJ-platform Subaru owners think about downpipes and cat-backs first. The up-pipe — that short section connecting the exhaust header to the turbo inlet — tends to stay out of mind until something goes wrong or a tuner flags it during a dyno session. At that point, you need the right part on your doorstep as fast as possible.
Ordering an up-pipe online sounds straightforward, but there are a few details that trip people up: fitment differences between model years, the EGT sensor question, which gaskets to order alongside it, and whether the retailer you’re buying from will actually ship it today. This article walks through all of it.
Fitment: Which Up-Pipe Fits Your Car
The EJ-series WRX and STI share a common up-pipe architecture across a wide range of years, but the split between 2.0L and 2.5L engines matters.
2002–2005 WRX (EJ20): The factory up-pipe on these cars includes a small pre-turbo catalytic converter. That cat is notorious for breaking apart under boost and sending ceramic debris straight into the turbo. Most owners replace it with a catless aftermarket unit or an OEM-style pipe without the cat. These cars also have an EGT sensor bung in the stock up-pipe — more on that below.
2006–2014 WRX (EJ25) and 2004–2021 STI (EJ257): These share the same up-pipe design. The factory unit is already catless on the STI across all years, and the 2006+ WRX dropped the pre-turbo cat as well. Fitment is consistent across this wide range, which makes sourcing parts easier. As one fitment reference confirms, the OEM up-pipe for this group covers the 2006–2014 WRX and 2004–2021 STI as a direct bolt-on.
A few things worth noting for cross-year swaps: up-pipes from 2002–2007 WRX and STI models are generally interchangeable, which gives you some flexibility when sourcing parts. If you’re running a 2002–2005 WRX and installing a catless pipe originally designed for the 2006+ cars, the pipe itself fits — but you’ll need to address the EGT sensor connector.
The EGT Sensor Question (And Why It Matters Before You Order)
This is the detail that causes the most post-install headaches, so it’s worth getting clear on before you click ‘buy.’
On 2002–2005 WRX models, the factory up-pipe has a bung for an exhaust gas temperature (EGT) sensor. The ECU uses this sensor to monitor the health of the catalytic converter in the up-pipe. When you install a catless pipe without an EGT bung, the ECU loses that signal and throws code P0546 — Exhaust Gas Temperature Sensor Circuit Malfunction. The standard fix is a 2.2K ohm, 1/2-watt resistor plugged into the EGT connector harness near the passenger-side strut tower. This tells the ECU it’s reading a normal temperature, preventing the CEL. The resistor value of 2.2K ohms corresponds to a healthy EGT reading as far as the ECU is concerned.
If your aftermarket up-pipe includes an EGT bung, you have the option of reusing the stock sensor — but most experienced Subaru tuners advise against it. A sensor sitting directly in the exhaust stream without the cat to moderate temperatures can overheat and eventually break apart, sending debris toward the turbo. The resistor approach is simpler and safer in most catless setups.
2006+ WRX and all STI models don’t have an EGT sensor in the up-pipe at all, so this entire discussion doesn’t apply. If you’re on a 2006 or newer platform, you can install a catless up-pipe without any sensor workaround.
If you’re running a Cobb Accessport or similar engine management, you can disable the EGT code in the tune directly, which removes the need for the resistor mod entirely.
Gaskets: Order These at the Same Time
An up-pipe swap means disturbing two gasket surfaces: the header-to-up-pipe flange at the bottom and the up-pipe-to-turbo inlet flange at the top. Both should be replaced any time the up-pipe comes off, regardless of how the old ones look. High heat cycles cause these gaskets to compress and take a set; reinstalling them risks an exhaust leak that’s annoying to track down and fix a second time.
STM Tuned stocks both OEM Subaru gaskets as separate line items. The OEM Up-Pipe to Header Gasket for 02–14 WRX / 04+ STi (part number 44022AA170) covers the lower connection on all EJ-series turbo models. The OEM Up-Pipe to Turbo Inlet Gasket for 02–14 WRX / 04+ STi handles the upper connection. Both are genuine OEM Subaru factory replacements and ship worldwide.
For those who prefer an aftermarket option at the lower flange, GrimmSpeed makes a multi-layer steel version that replaces OEM part 44022AA170 and fits the same 2002–2014 WRX and 2004+ STI range. STM carries that as well.
If you’re also pulling the downpipe during the same service — common when doing a full exhaust refresh — STM stocks the OEM Turbo to Downpipe Hardware kit for 2004+ STI and 2002–2014 WRX, sold as a full ten-piece kit or individually.
Ordering these alongside your up-pipe in a single cart means one shipping label, one delivery, and no waiting on a second package before you can button everything up.
How STM Tuned’s Same-Day Shipping Actually Works
STM Tuned (mtuned.com) ships over 90% of orders the same day they’re placed. That number matters when you’re trying to get a car back together before the weekend or before a scheduled dyno appointment.
The store is based in Webster, NY and has been operating since 2007. Their catalog covers OEM replacement parts, aftermarket upgrades, and their own USA-made STM-fabricated products. For in-stock items like OEM gaskets and most up-pipe options, the same-day rate applies — orders placed early enough in the business day go out that afternoon via the carrier of your choice.
For buyers in the continental US, that typically means a 1–3 day transit window depending on your zone from upstate New York. Canadian and international buyers can order as well — STM ships worldwide, which is confirmed directly on individual product pages for OEM gaskets and hardware.
One thing to keep in mind: STM also fabricates their own exhaust components in-house in New York. Hand-welded pieces like their STM cat-back and axle-back exhausts carry a longer lead time (listed as 1–14 days depending on the product) because they’re built to order. Up-pipe gaskets and OEM hardware don’t have that lead time — they’re shelf stock.
If you’re comparing options, the key question is whether the retailer you’re looking at actually has the part in hand. Some competitors list items as available and then drop-ship from a distributor, adding days you didn’t plan for. STM’s same-day rate reflects inventory they physically stock in Webster.
Putting the Order Together
To summarize the practical steps:
- Confirm your engine and model year. EJ20 (2002–2005 WRX) vs. EJ25 (2006–2014 WRX, 2004–2021 STI) determines whether you need to plan for the EGT sensor situation.
- Choose your up-pipe. OEM replacement or aftermarket catless — both are valid depending on your goals and local emissions requirements.
- Add both gaskets to your cart. Header-to-up-pipe and up-pipe-to-turbo-inlet. Don’t skip these.
- If you’re on a 2002–2005 WRX going catless, pick up a 2.2K ohm, 1/2-watt resistor for the EGT connector, or plan to address it through your ECU tune.
- Place the order before the daily cutoff at STM Tuned to hit the same-day shipping window.
The WRX STI community on the EJ platform has been doing this swap for over two decades, and the parts ecosystem around it is well-established. The fitment is consistent, the gaskets are cheap insurance, and getting the right retailer means the parts are at your door in days rather than weeks. STM Tuned’s Subaru STI performance parts catalog covers everything from OEM replacement hardware to full exhaust systems for the EJ25 platform — a useful starting point if you’re planning a broader exhaust refresh alongside the up-pipe swap.