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Time to read 7 min
Ever hear a turboed Subaru sound absolutely angry as it's wide open throttle? It sounds amazing right? It's the kind of sound you hear and are instantly like, I need my Subaru to make the noises too please but maybe you're not sure what that sound is or how to obtain it. Well, you're in the right place! Welcome back to part two where we cover Go Fast Bits wastegates! In this article we'll cover what are they, how they work, pros/ cons and a few options that GFB has for our Subarus.
A wastegate is a valve that controls the exhaust gas flow and allows the gases to bypass the turbine side of the turbocharger. The purpose of the wastegate is to help control the speed (RPM) of the turbo and when the set spring pressure is reached it also regulates boost pressure. Without the wastegate too much boost pressure would be able to build up, which would damage the engine. Having the wastegate take on some of the exhaust gases, we're able to minimize wear and tear on the engine while ensure the engine can run at as efficiently as possible.
There's two types of wastegates internal and external - we'll start with the more common, internal waste gate. Internal wastegates are usually bolted to the exhaust housing of the turbo and made up of a flapper valve, crank arm, rod end and actuator. How it works is as boost is being built up it's also creating pressure, that pressure goes through a vacuum line leading into the pneumatic actuator. The actuator is made up diaphragm and a spring - when the pressure is at the specific level the diaphragm will push up on the spring which then pushes on the crank arm. When the crank arm is pushed up, the rod end that's attached to the flapper valve will then open up the flapper valve. The flapper valve is the valve that controls the exhaust gas flow - when the valve is open it's allowing the exhaust gases to bypass the turbine and go into the exhaust system. The boost level can be controlled by the spring rate, if the spring is stiffer it's going to require more pressure to open it up which allows for more boost. Whereas if it's a lighter spring, it'll be easier to push up on and it'll provide lower boost levels.
The pros to having an internal wastegate set up is mostly space, cost and I would even argue the simplicity. Because these are mounted to the turbine housing, these take up an extremely smaller footprint than an external wastegate. Having a price point where most internal waste gates are well under the $300 range is helpful as well, especially since we know how expensive modding our cars is. Which leads to some of the cons - the internal wastegates are reliable for low boost and are slower at responding to change in boost pressure due to how they're set up to function. Internal wastegates are also susceptible to increased heat buildup and bypass flow which causes turbulence in the exhaust housing resulting in increased backpressure and turbo lag. They also have a smaller valve which limits flow capabilities, making it a better choice for applications that are on lower boost levels and not a high performance track car.
Go fast bits offers a solution to lessen the cons for some of us Subaru owners who want to keep the internal wastegate set up but have a bit more performance and efficiency. GFB’s WGA 7304 is for Subaru WRX models 97-07 with the factory TD04 turbo. GFB's WGA 7304 uses a high-performance actuator that has a larger diaphragm area when compared to the OEM one. This allows for it have less of a chance of bypass flow and lag due to the backpressure not being able to override the flapper valve as easily. By eliminating less chance of bypass, you increase a more stable and reliable boost control! GFB also made some improvements on the crank arm (rod) making a longer stroke available to allow increased boost pressure without having to adjust the springs. When it comes to the springs, GFB WGA 7304 has 3 sets of springs - the 5psi and 7psi springs come installed to make a base pressure total of 12psi, and they also include a separate 10psi spring for other tuning options.
Now on to my favorite type of wastegates - the external. External wastegates consist of a top cap, which contains the actuator (spring and diaphragm assembly), the body of the wastegate, the valve, valve seat and the v band clamps and weld on flanges. The external wastegate acts like the internal wastegate does - When the built up pressure has exceeded the spring rate it will then cause the spring to open the valve ( which is more like a poppet valve in this application), and allows the exhaust gases to travel through the valve instead of the turbine side. Now a few key differences are this application has a valve seat which is to help ensure a tight seal which improves the response time of controlling boost. You'll also notice it also has v band clamps as well as some weld on flanges due to the external wastegate to be welded on before the turbine housing inlet, i.e., the exhaust manifold or headers. The external wastegate can route exhaust gases back into the exhaust system or it can be vented to the atmosphere, which is the open dump aggressive sound we love to hear on race cars as they're WOT.
If your set up requires an external wastegate you'll need to do some fabrication work to tie it into the turbo's exhaust system - if you opt to have the wastegate to open dump into the atmosphere, you'll need to fab a dump tube or some way to allow the exhaust gases to flow out and away from the engine. It's important to make sure the hot exhaust gases are routed in an area that will keep them away from anything that could melt and away from the engine bay due to possible air fuel mixture interruption through the intake. Another con of having an external wastegate is that they're more expensive than an internal, they start at about the $500 range. It's an additional cost if you need someone to do any of the wastegate fabrication also. Besides that, the benefits of the external wastegate outweigh the cons. External wastegates offer better boost control due to having a faster response time, different valve sizes, valves that are usually larger and valves that also have a seat which as we mentioned keep a tight seal which also improves the response time to controlling boost. External wastegates (recirculated) also provide improved turbine performance due to their ability to allow the bypassed gas into the exhaust system further downstream ( less risk of turbulent air) or it can be dumped into the atmosphere. Also they allow for better heat control as well as easier serviceability due to the design.
Go fast bits offers a variety of wastegates for our Subarus! They offer an EX38, 44 and 50 - all names directly relate to the sizing, so Ex38 is for a 38mm Wastegate and so on. GFB makes their external wastegate bodies out of 253MA chromium-nickel stainless steel, meaning it can withhold high temperatures and resist oxidation at temperatures up to 1150 C. This material not only allows strength in high and low temperatures (-150 C) but, is also has a very good weldability properties. Their valves are made of billet stainless, ensuring they also have high properties of strength, hardness, and ductility. GFB also makes their diaphragm out of a nomex reinforced silicone adding to the durability their wastegates have against heat and flames. Due to the high quality materials alone, one can trust these wastegates can handle the abuse of some serious power being made. GFB's external wastegate are also made to be a compact size so they can fit in small spaces and are designed to have a universal fitment while maintaining their ability to have a high flow capacity.
When it comes to controlling the boost on wastegates one can also control it by using a boost controller, instead of just using wastegate spring pressure (which is what we described in each example above) . There's manual and electronic boost controller options where the actuator can be manipulated into opening or closing based on desired boost levels. There's so much to cover on the boost control topic we'll save for a another article. The important thing to take away from this is the boost controller helps the turbo operate within it's efficiency range by the wastegate maintaining a set boost pressure which helps the engine run strong, (fast), and healthy.
So now you're able to decide if you want to be stealthy, more stock with some umphf, or if you want to go full race car with the open dump! Whichever wastegate you choose make sure it's fitted for your specific application, and you consult your tuner for boost control options to ensure the most efficient set up. As you can see, Go Fast Bits makes a great option to consider when deciding between the companies who make wastegates. Their team is also available to help with questions you may have if you're stuck on which would fit best for you and are happy to help with service questions. Since we covered all the things from GFB that make cool turbo noises - up next, we'll talk about the top five things you'll need if you're interested in tracking your car so you can hear those BOVs/Wastegates sing at their full potential.
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