Ever dream of giving your car a serious power boost? Look no further than a turbocharger! But before you dive into the world of forced induction, understanding different turbo types and how they affect your ride is key.

This guide will equip you with the knowledge to make an informed choice when selecting a turbocharger. Let's break it down:

Turbo Types 101:

Regular Turbo: This is your classic turbo, offering a simple upgrade path with good power gains. Think of it as the "bolt-on and go" option. Popular choices for Subarus include the VF-30/34/22 and 16/18/20G series.

Twin Scroll Turbo: This advanced setup utilizes a special exhaust design for faster spool-up (boost response). However, it requires specific exhaust components like an equal-length header for optimal performance. Think faster boost, but with a slightly higher installation cost.

Rotated Mount Turbo: These are high-performance monsters that offer massive power potential. However, due to their size it prevents it from fitting in the stock location and must be mounted at a slightly different angle. They usually require custom piping, a front-mount intercooler, and professional installation. Think serious power gains, but at a significant investment.

Twin Turbos: While rare for Subarus, twin turbos offer incredible power, but at a hefty price. They require extensive fabrication, tuning, and expertise to function reliably. Think ultimate power for the dedicated enthusiast.

Turbo Terminology Explained:

CHRA: The heart of the turbo, housing the rotating assembly (blades and shaft).

Compressor/Turbine: These are the two main sections of the turbo. The compressor forces air into the engine, while the turbine uses exhaust gases to spin the compressor.

Compressor Map: A crucial tool for understanding a turbo's efficiency range and how it will perform with your engine.

Trim: This ratio indicates the compressor's ability to flow air (higher trim = more power, slower spool, lower trim = faster spool, less power).

A/R (Area/Radius Ratio): This affects how exhaust gasses flow through the turbine, influencing spool-up and peak power (lower A/R = faster spool, less top-end power, higher A/R = slower spool, more top-end power).

Wastegate Control: Bypassing Exhaust Flow

Internal vs. External Wastegates: Both regulate boost pressure by diverting exhaust gases away from the turbine, limiting compressor output.

Internal Wastegates: Integrated into the turbo housing, they offer a simpler design but may struggle with larger turbos.

External Wastegates: Offer greater control and flow capacity, ideal for high-performance setups. They can be configured to bypass the internal wastegate entirely.

Wastegate Tuning: A spring mechanism within the wastegate determines the boost pressure activation point. A stiffer spring (exceeding 50% of target boost) can lead to boost creep.

Boost Dynamics: Understanding Pressure and Lag

Boost Creep: Unwanted increase in boost pressure beyond the setpoint, often caused by an undersized wastegate or high exhaust temperatures. It can be addressed through wastegate adjustment or upgrades.

Boost Spike: A momentary surge in boost pressure exceeding the target, typically due to a sluggish boost controller struggling to adapt to rapid changes in engine conditions. Improper turbo sizing can also contribute.

Anti-Surge Ports: Safety features found in large turbos, these channels allow excess air to bypass the compressor wheel, preventing compressor surge (abrupt pressure reversal).

Boost Threshold: The engine RPM at which sufficient exhaust flow is generated to overcome the turbine inertia and create positive pressure (boost) in the intake manifold.

Turbo Lag: The time delay between throttle actuation and the onset of boost. This is influenced by turbo size, exhaust flow characteristics, and wastegate behavior.

Optimizing Performance: Porting, Clipping, and Hybrids

Porting and Polishing: Smoothing internal surfaces of the compressor and turbine housings improves airflow efficiency.

Turbine Clipping: Removing material from the edges of turbine blades alters the flow profile, increasing exhaust gas flow at the expense of spool-up speed (time to reach boost).

Hybrid Turbos: Combining components from different manufacturers (typically MHI or Garrett) allows for customized performance characteristics.

Selecting the Right Turbo: Beyond Hype

Choosing the right turbocharger is a balancing act between desired power output, responsiveness (boost lag), and daily drivability. Here are some key considerations:

Research is Key: Don't chase trends! Compressor maps and consultations with experienced tuners are essential for selecting the optimal turbo for your specific goals.

Understanding Nomenclature: Familiarize yourself with the naming conventions of major turbo manufacturers like MHI, IHI, and Garrett. This aids in deciphering turbo specifications.

Matching Needs: Consider factors like engine displacement, power goals, and driving style when selecting the turbo size and characteristics.

By understanding these technical aspects, you can make informed decisions when exploring the exciting world of turbocharged performance. Remember, proper tuning and installation are crucial for safe and reliable operation of a modified engine.

Choosing the Right Turbo:

There's no "one size fits all" when it comes to turbos. Here are some key things to consider:

Power Goals: How much extra power are you looking for?

Driving Habits: Daily driver or weekend track warrior?

Budget: Regular turbos offer good value, while high-performance options require more investment.

Research: Compressor maps, tuner recommendations, and expert resources like Corky Bell's "Maximum Boost" book will guide you further.

Beyond This Guide:

Remember, this is just a starting point. Before making a decision, talk to your tuner and a reliable turbo vendor. They can help you choose the perfect turbo to unleash the hidden power within your car!