Let’s say you’re just dipping your toes into the glorious pool that is the world of turbocharged vehicles. You have your spoolie boi picked out, and you know who’s going to help you with tuning the engine once it’s all together. What you don’t know, though, is what you’re going to do about boost control in the form of a wastegate. Side note: some turbos have a wastegate built in, and if you’re using one of those turbochargers, then this article isn’t for you. In the interest of education (both for ourselves and for you), we reached out to Turbosmart’s Marty Staggs, who has his hands in more turbocharged racing programs than he could count. Important to note about Marty’s relationship with boost control is that it’s not centered around one form of motorsports; his expertise runs the gamut from time attack to drifting to drag racing. So when he speaks, people listen. It’s kind of like EF Hutton, although only people of a particular vintage will get that reference.
Before we get started, let’s talk about what a wastegate does, and why it’s essential to a turbocharged engine combination. A wastegate is a control valve; it dictates the flow of the exhaust gas as it passes from the engine to the turbocharger, and in effect, diverts the gases away from the turbine wheel to control the wheel’s speed. Controlling the speed of the turbine wheel also regulates the speed of the compressor wheel—which is attached to the turbine shaft—and has the added effect of governing engine power.
When it comes to selecting the right wastegate for a particular application, since there is no “one size fits all” solution, Staggs has a simple suggestion.
“They need to call a trusted source. Like us, or their tuner, or their engine builder, or someone that has experience. There are a lot of things that factor into choosing the right wastegate. It’s easy to have too small of a wastegate. It comes down to experience; I’ve been turbocharging vehicles since 1984, so I’ve got a lot of experience. I’ve learned, I’ve seen, I’ve personally used and tried different things, so I have a pretty good idea of what works,” he explains.
Several factors must be taken into account when selecting a wastegate, but perhaps even more critical than the specific wastegate choice is the design of the exhaust manifold. The manifold fabricator must take into account wastegate placement from the initial design—not as an afterthought—because wastegate placement is critical to the operation of the unit and controlling the turbocharger. As the number of turbo exhaust manifolds on the market increases rapidly due to mass production capabilities, so, too, does the number of exhaust manifold designs that are not optimized. This is due to the manufacturer not understanding the ramifications of wastegate placement and how that placement affects the gate’s operation.
“Exhaust manifold design has an important play in how the wastegate works. That exhaust manifold might not be thought through—it’s about packaging, so they’ll make it where it’ll fit, and the wastegate’s kind of an afterthought. They’ll put a flange for a 45mm wastegate on it and say ‘that should be good,’ but you don’t know what turbo the dude’s going to put on the car, or how hard he’s going to push it. You see it, especially with 2JZs and some of these other engines. Turbocharger technology and what people are doing has advanced to a far higher level than maybe that manifold design has. So then the manifolds tend to be a bit inadequate; they’ll buy a wastegate that will fit on the flange, have a creep issue, and immediately think there’s a problem with the wastegate. More often than not, it’s the manifold design. The best manifolds have a smooth and straight flow path to the wastegate,” he says.
He uses the term “wastegate priority,” which means that the exhaust flow seen by the wastegate has, at a minimum, an equal priority with the exhaust flow seen by the turbine. This allows the wastegate to work correctly and regulate the boost. Some of those manifolds he mentions that have a substandard design put the wastegate into a situation where it only sees the exhaust flow from a couple of cylinders and not the whole engine. This creates a multitude of problems, none of which you want when trying to maximize a boosted combination.
In this instance, the exhaust flow can be thought of as a liquid (water) to visualize what happens as the exhaust moves from the engine through the exhaust manifold and into the turbine. The wastegate needs to see as close to a straight shot from the exhaust flow as possible. When the gate is stuck on the side of the pipe at a 90-degree angle, the flow to the gate happens as a result of the exhaust backing up in the pipe (backpressure) rather than its natural flow as it moves into the turbo. The bottom line: the poorer the wastegate placement/manifold design, the larger the wastegate will need to be to achieve the same level of control.
“If you want to make a lot of boost, that’s easy—you don’t even need a wastegate. The wastegate’s job is to keep the shaft speed in check. The wastegate helps you control the boost and keep it at a certain level, but if you want massive boost, the gate’s going to be closed more often than not. The balancing act is to know your operational range,” he explains.
Hemi and 481X engines used in drag racing classes like Radial Vs. The World make well north of 4,000 horsepower without batting an eye, and we can attribute much of this to the controls offered by today’s technology.
In applications such as these, the wastegate’s performance is critical.
“They want very little boost on the starting line. And as they go down the track, they want to start to bring the boost in quickly. That range of boost they want requires a very large wastegate. We have to have a lot of flow to control that 481X with monstrous turbos that will make 80-plus pounds of boost out the back end—but he only wants 3 pounds to leave the line. In those applications, the guys building those exhaust systems know; those headers are built with great wastegate priority. Our 60mm wastegates are used in those applications, and it does everything they need,” says Staggs.
As part of its relationships with so many of the industry’s leading race teams, Turbosmart has an intimate look into the tuning strategies they are using to achieve results on the track. Staggs says that they’ve redesigned their wastegate four times—the current model is the Gen V—to stay ahead of what the tuners need in terms of wastegate performance.
Technology never stands still. Companies like Garrett are continually refining the performance capabilities of turbochargers, and engine management systems manufacturers like AEM Performance Electronics, FuelTech, Haltech, and Holley are always working to implement more powerful tuning calibration strategies using the research they perform and the feedback they get from their racers.
Marty puts it simply: “They’re always working on these systems, these combinations, to be more efficient, to flow more, to do more. Likewise, we are constantly working on getting our wastegates to flow more, weigh less, and have more control. That way, we can help these guys make that power usable. Knowing that a lot of times the wastegate isn’t in an ideal location, it puts more impetus on us to create a very high-flowing wastegate.”
With the fifth generation of the company’s wastegates as a significant part of our discussion, I asked him to detail what makes the Turbosmart product perform so well.
“Compare it to a cylinder head. Look at everything that’s happening in the bowl area, just on the other side of that valve. It has to have an optimized configuration after you get past the seat. All wastegates out there in the world have a single cut on the valve and the valve seat for the mating surface. Our Gen Vs have a three-angle valve job, straight out of the cylinder head playbook. The valve itself is 3-D contoured, so it’s not just a flat valve. It’s more like a mushroom head and has a profile to it, so when the valve starts to lift off the seat, you get a massive amount of flow compared to a valve that would be flat. The air wants to flow around it instead of bouncing off of it,” he explains.
Additionally, the valve’s contours make a big difference when it comes to pinning the wastegate shut in higher-RPM, high-flow situations, to increase boost pressure. Staggs explains that flat-faced valves do not like to close against this pressure, but the 3-D contoured valve with the rounded face is easier to close as the air flows around the valve more easily. This capability is especially useful in the higher-echelon drag racing classes like X275 and Radial Vs. The World. These cars are using the CG (Compressed Gas) version of the GenV wastegates that are designed for applications where CO2 is used to control the gate’s operation. The CG wastegates are also used in World Rally Championship competition.
“There isn’t a single area on the new Gen V wastegates that has not been looked at and optimized for the absolute most flow and control,” he says.
The next step in wastegate improvement from the Gen V gates—which are already state-of-the-art—comes in the form of the company’s all-new GenV Electronic HyperGate 45 and PowerGate60 external wastegates. These use a combination of the GenV valve architecture with an electronic motor control configuration rather than traditional CO2 control. I saw these at PRI last year and fully expected to see them in wide use this season given the capabilities of the design, but as of yet, the setbacks posed by the coronavirus has them in the hands of a select few sponsored teams at this time.
“At some point, the ECU will completely control the wastegate, there won’t be any CO2, and it’ll just be another map like your fueling table. Because it’s completely controlled by the ECU, you say “at this, I want this,” and it’s going to do it. If the G-meter gets out of control and the thing is wheelieing, you can have the wastegate open to reduce the boost. You could do boost by corner on a road course, boost by Gs, boost by wheelspeed. It’s up to your imagination because you’re going to write your map. There is no spring in the wastegate so that you can go from no boost to all the boost in milliseconds. This is next-level, game-changing stuff,” he says.
The electronic motor and gearbox inside the electronic wastegate make it an active, directly controlled device that can be programmed to do what you want it to do, exactly when you need it done. This is unlike CO2 wastegates where there are a couple of solenoids and a pressure regulator to worry about—not to mention the concern about whether the crew guy remembered to turn on the CO2 bottle.
If you’ve got a turbo project you’re working with, Marty Staggs and his Turbosmart team are an excellent resource. There’s a reason you see their products on engines used by top racing teams like Mike Murillo’s No Prep Kings Mustang, the Firepunk Diesel gang, and many, many others. We appreciate him taking time out of his busy schedule to assist us with the compilation of this article, to help educate us—and hopefully you—in the process.