IWG vs. EWG: A Comprehensive Guide for Subaru EJ Engine Performance

Your ultimate resource for understanding wastegate choices and maximizing your Subaru's potential.

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Today, we're incredibly excited to delve into a topic that stirs passionate debate and is crucial for anyone looking to maximize the performance of their turbocharged Subaru EJ engine: the fundamental difference and resulting benefits (or trade-offs) of choosing between an Internal Wastegate (IWG) and an External Wastegate (EWG) setup. As professionals dedicated to bringing you the pinnacle of turbo technology and performance upgrades, we understand that making the right choice is paramount to achieving your vehicle's full potential.

This discussion isn't just about selecting a part; it's about fine-tuning the very heart of your boost control system to unlock greater efficiency, power, and reliability. We're drawing directly from the experiences and knowledge shared within the community to provide you with a clear, comprehensive breakdown. Let's explore why this distinction matters and what it means for your build!

IWG vs. EWG: The Fundamental Difference

Understanding how exhaust gases are managed is key to understanding wastegates.

• Internal Wastegate (IWG): This is the integrated solution typically found on factory turbochargers. A flap within the turbine housing opens to divert exhaust gas away from the turbine wheel, regulating boost pressure.
• External Wastegate (EWG): This system uses a separate, dedicated valve installed on the up-pipe before the turbocharger. When the desired boost pressure is reached, the EWG valve opens, releasing excess exhaust gas either to the atmosphere (via a "screamer pipe") or back into the exhaust system downstream of the turbo.

Now, let's weigh the considerations for each setup.

Internal Wastegate (IWG): The Integrated Approach

The IWG is the standard for simplicity and cost-effectiveness in OEM applications. It's a compact and integrated part of the turbocharger. However, particularly when pushing for higher power levels, the IWG can sometimes struggle with precise boost control. A common issue encountered is "boost creep", which occurs when the internal wastegate port isn't large enough to bypass all the excess exhaust gases at high engine loads or RPMs, leading to uncontrolled boost pressure that exceeds the target. While modifying the IWG, such as porting, can sometimes help mitigate minor boost creep, it may not be sufficient for more aggressive performance goals.

External Wastegate (EWG): Precision and Performance

Switching to an EWG system involves installing an up-pipe that is specifically designed and flanged to accept an external wastegate. Additionally, the factory internal wastegate must be disabled or held shut. A widely recommended method for doing this on a stock turbo is using a bracket designed for this purpose. Kinugawa Turbo Systems offers an Adjustable IWG to EWG Bracket Convert Kit for precisely this kind of conversion.

The advantages of an EWG setup, frequently shared by those who have made the transition, highlight its capability for superior control and increased performance.

Pros of Running an EWG:

• Superior Boost Control: EWGs offer significantly better control over boost pressure compared to IWGs. Their dedicated, often larger, valve provides more precise regulation. When coupled with an advanced aftermarket boost control solenoid (BCS), near-perfect boost management can be achieved.
• Eliminates Boost Creep: A primary reason enthusiasts upgrade to an EWG is to combat or entirely eliminate boost creep. By effectively bypassing excess exhaust gas before it reaches the turbine, the EWG ensures boost levels remain accurately at the target.
• Improved High-RPM Performance: An EWG system can help the turbo maintain target boost pressure more consistently at higher engine speeds. This is particularly advantageous for setups running supporting modifications like race fuel or ethanol (E85), which allow for higher boost targets throughout the RPM range.
• Faster Turbo Spool: EWGs can contribute to quicker turbo spool-up. This is because the wastegate remains completely closed until boost regulation is required. When it does open, it directs exhaust gas away from the restrictive turbine housing.
• Increased Power Potential: By allowing exhaust gases to bypass the turbine housing, which can be a significant restriction in the exhaust path, an EWG effectively makes the turbo's hot side behave like a much larger one. This reduction in backpressure and improved flow can lead to noticeable power gains, especially at higher RPMs where the IWG can become a bottleneck. Realistic gains of 20+ wheel horsepower (whp) at redline and 10-15 whp or more at peak have been observed, even on smaller turbos. Some sources suggest smaller turbos may see proportionally larger benefits from an EWG conversion than larger ones.
• Distinct Exhaust Note: When vented to the atmosphere (VTA), the sound of an EWG opening to release pressure is a unique and often sought-after characteristic, sometimes referred to as a "screamer pipe".

Cons of Running an EWG:

• Noise Level: Venting the EWG directly to the atmosphere is considerably loud. This "screamer pipe" sound can be problematic in urban areas, potentially attracting unwanted attention, and may be restricted at certain motorsports events like auto-cross.
• Recirculation Reduces Benefit: While the EWG exhaust can be routed back into the main exhaust system to lower noise, recirculating the gases can diminish the overall performance gains compared to venting to the atmosphere. The design of the recirculation plumbing is critical; poor designs can create turbulence and negate the flow benefits.
• Additional Cost and Hardware: Implementing an EWG requires purchasing a new up-pipe flanged for the external wastegate and a method to disable the stock IWG. An aftermarket boost controller (either manual, a boost control solenoid, or an Electronic Boost Controller/EBC) is also typically necessary or recommended for optimal control. These are additional expenses not present in a basic IWG setup.
• Potential for Being Overkill on Smaller Turbos? (Debated): Some opinions suggest that an EWG might not provide significant benefits or could be considered overkill for very small turbos, such as a VF39. However, other experienced voices argue strongly that even smaller turbos benefit by improving hot side flow.
• Wastegate Sizing and Quality: Selecting the correct size and a high-quality external wastegate is important. Issues like blown gaskets have been noted with some 38mm EWGs, leading to recommendations for larger 44mm units, often utilizing more reliable V-band clamps instead of traditional gaskets.
• Not Always the First Mod: Compared to other common performance upgrades like a cold air intake (CAI), turbo-back exhaust (TBE), fuel system enhancements, a larger intercooler, or an inlet pipe, an EWG system might be considered less impactful in terms of "bang for the buck" as an initial modification, depending on the desired power level and goals.

EWG Sizing: Finding the Right Fit

The debate between using a 38mm or 44mm external wastegate is common. One theory suggests that a 44mm wastegate is more suitable for lower boost applications because it needs to bypass more exhaust gas, requiring a larger valve. Conversely, a 38mm wastegate might be sufficient for higher boost setups where less bypassing is needed. However, professional advice can sometimes differ from this general theory. As mentioned, one source recommends avoiding 38mm EWGs due to potential gasket issues and favors 44mm units with V-band clamps for better reliability. Ultimately, consulting with your chosen professional tuner is crucial to determine the optimal wastegate size and spring pressure based on your specific turbocharger, engine setup, and performance target. Kinugawa Turbo Systems understands the need for options and offers components like the adjustable IWG to EWG bracket convert kit to facilitate these transitions. Up-pipes designed for external wastegates are available from various manufacturers.

What You Really Need for a Successful EWG Setup

Simply bolting on an EWG and an up-pipe is just one piece of the puzzle for a reliable and high-performing system. A holistic approach to modifications is essential.

• IWG Disablement: The stock IWG must be effectively held shut. Using a specialized bracket is a common and recommended method.
• EWG Up-pipe: A new up-pipe specifically flanged for the external wastegate is mandatory. These are available for various Subaru models.
• Boost Control: While not always strictly required depending on the tuning approach, a boost controller (manual, aftermarket solenoid, or EBC) is highly recommended for precise boost management.
• Comprehensive Supporting Mods: To truly capitalize on the improved flow and control offered by an EWG, particularly for higher power, supporting modifications are necessary. Upgraded fuel system components, including a fuel pump, injectors, and potentially fuel rails and lines, become crucial, especially above 350 whp, as OEM parts can lead to fueling inconsistencies or exacerbate known issues. A free-flowing intake system and an upgraded intercooler system are also vital to support increased airflow and manage air charge temperatures.
• Professional Custom ECU Tuning: This cannot be stressed enough. Any significant performance modification like an EWG requires custom ECU tuning by a qualified professional. This ensures the engine operates safely, optimizes the benefits of the modifications, and prevents potential engine damage. Relying on stock ECUs or generic tunes with these modifications is highly risky.
• Compatibility: Always double-check component compatibility with your specific Subaru model, year, and engine variant. Be aware of potential differences, such as those for RHD vehicles or clearance issues that might require other adjustments.

Comparison Table: IWG vs. EWG

Engage with Kinugawa Turbo Systems!

Choosing the right wastegate setup is a pivotal decision for your Subaru's performance journey. At Kinugawa Turbo Systems, we are committed to providing the high-quality turbochargers and components you need to achieve your goals. Our Adjustable IWG to EWG Bracket Convert Kit is just one example of how we support enthusiasts looking to upgrade their boost control. When paired with the right up-pipe and a comprehensive tuning strategy, an EWG system can truly transform your vehicle.

We encourage you to explore our range of performance products designed for various Subaru models, including turbochargers capable of supporting ambitious horsepower figures. Ensuring the authenticity and quality of your parts is also easy with our anti-counterfeit tags and cloud system verification.

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