What is an exhaust system and what does it do?

An exhaust system is a network of pipes that funnels exhaust gases away from the engine and out of the vehicle. It plays a key role in:

- Reducing engine heat

- Controlling emissions

- Influencing engine performance (to some extent)

Stock vs. Aftermarket Exhaust Systems

Stock Exhaust:

Designed for a balance of performance, emissions control, and noise reduction.

Typically uses a catalytic converter to reduce harmful emissions.

Aftermarket Exhaust:

Often designed to improve performance by increasing exhaust flow.

May achieve this by using a higher-flowing catalytic converter or removing it altogether (not street legal in most areas).

Can also alter the sound of the exhaust.

Types of Aftermarket Exhaust Systems:

There are three main categories of aftermarket exhaust systems, depending on which part of the stock system they replace:

Turbo back exhaust (TBE): Replaces everything from the turbocharger (in turbocharged engines) to the downpipe. Offers the most significant performance gains, but also the most expensive and involves the most modification.

Cat back exhaust (CBE): Replaces everything from the catalytic converter back. Offers a balance between performance gains, cost, and modification.

Axle back exhaust (ABE): Replaces only the muffler, offering the least performance improvement but also the easiest installation and lowest cost.

Important Note:

Modifying your exhaust system can have legal and environmental consequences. Always check local regulations before installing an aftermarket exhaust.

 Aftermarket Exhaust vs. Stock:

Aftermarket exhausts aim to improve performance by enhancing exhaust flow.

They typically achieve this through:

- Larger diameter pipes

- Higher-flowing catalytic converters (or removing them entirely, which may not be street legal)

Fitment Considerations:

Year/Model Variations: While most aftermarket exhausts designed for 2002-2007 WRX/STi fit various models within that range, there can be exceptions for:

2006+ WRX: Uses a unique downpipe/midpipe combo. Requires a "long downpipe" for replacements.

2008/2009 WRX: Uses a Legacy GT downpipe.

2008/2009 WRX/STi: Axle-back exhaust mounts differently.

OEM vs. STi Exhaust: While the STi exhaust has slightly larger pipes, its catalytic converter negates any performance gains. You might consider the STi axle-back for a slightly louder sound.

Sound and Performance:

Sound:

Exhaust sound is subjective. There's no single "best" sounding exhaust. Research and listen to sound clips online or seek out cars with the exhaust you're considering in your area.

Performance Gains:

Gains vary depending on the exhaust type, car modifications, and dyno testing methods. Here's a general range:

TBE: 20-30 HP

CBE: 5-15 HP

ABE: 5-10 HP

Other Buying Factors:

Material:

Exhausts come in mild steel, stainless steel, and titanium. Stainless steel offers a good balance of durability and corrosion resistance.

Diameter:

Larger diameters are suitable for higher horsepower applications

(2.5" for 300-350 HP, 3.0" for 500-600 HP, 3.5" for 600+ HP).

However, a larger diameter than needed won't necessarily provide more power.

Catalytic Converter:

Consider your state's emissions regulations when choosing between high-flow catalytic converters or catless options.

Drone:

This is an annoying buzzing sound at highway speeds. Wagons are more prone to drone due to the lack of a trunk.