Holley Performance Shows Us How Turbos Work
Ever asked yourself, how do turbochargers work? Turbochargers, big and small we love them all! Let’s all give a big shout out to the Swiss not only for their fine chocolate but also for giving us Alfred Buchi. Because of this Swiss engineer, turbochargers have been increasing good since 1905. And since their invention, they have become one of the most popular methods of forced induction available. Adding more air and fuel to your engine is a sure-fire way to increase the horsepower output. Whether it’s on land, at sea, or in the air, most gasoline engines, even 2 stroke, and Rotary engines can benefit from turbocharging.
Before the invention of turbos and forced induction, options to increase an engine’s horsepower was pretty limited. Sure, you could increase the displacement of your engine by adding more cylinders or even increasing the size of the current cylinders. But, this can be complicated and very expensive. Adding a turbo, on the other hand, is a much simpler and easier way to accomplish similar or even better power results.
Turbochargers effectively increase an engines output by forcing more air into the cylinders. Typically, a turbo provides 6 to 8 psi of boost, but depending on the application, they can add as much as 50psi or more of tire shredding boost. At sea level, normal atmospheric pressure is 14.7 psi, so by boosting the intake charge by 6 to 8 psi, you are essentially putting about 50 percent more air into your engine. Which in theory should net a 50 percent increase in power.
Unfortunately, due to a number of factors like heat, friction, exhaust restriction, and a little property called inertia, a turbo isn’t 100% efficient. So, a more realistic expectation would be a 30- to a 40-percent increase in power depending on your particular set-up. Let’s take a closer look at the inner workings of a turbo and some of the components involved.
Turbocharging is really quite simple. You attach a turbo to the exhaust manifold or header on your engine and then use the exhaust gasses that would normally just go out the tailpipe, to spin a turbine at insanely high speeds, sometimes nearing 150,000 rpms. But the turbine itself only makes up one side of a turbo. The turbine is directly connected to the compressor side by a common shaft. The compressor side is where we get our boost and works by pulling fresh air through the air filter and into the center of the rotating blades.
Spinning at a high velocity, the rotational forces of the blades force the air outward compressing it and converting the high-velocity, low-pressure air stream, into a high-pressure, low-velocity air stream through a process known as diffusion. Compressing the intake charge enables the engine to squeeze more air into the cylinders. More air means that we can add more fuel, thus creating more power with each compression stroke, all without having to increase the engine displacement.
Turbos are a great way to increase power on fuel injected engines, but they can also be used with carbureted set-ups as well. With a carburetor you have a few options, you can install a specialized blow through carb on your intake along with a carb hat. Or you can use a standard carburetor, mount it before the turbo, and draw the air through it. The 3rd option is to use a standard carb mounted inside a sealed box which is bolted to your intake and then pressurize the entire box with the turbo.
Unfortunately, like most things, power doesn’t come free. Anytime air is compressed it creates heat, and as the air is heated it expands leaving you with less air or more importantly less oxygen molecules in the same amount of space. A small portion of the pressure increase that a turbo provides, can be attributed to this heating of the incoming air. The end goal is to increase the power of the engine by getting more oxygen molecules into the cylinder, not necessarily more pressure. This is the primary reason why we use intercoolers. The intercooler works similar to a radiator, with the exception that we pass air through the inside to be cooled, rather than water. An intercooler can increase your power gains by cooling the warmer pressurized air that’s coming from the compressor before it makes its way into your engine. The intercooler provides a cooler, denser air charge that contains more oxygen molecules than the warmer air does.
There are other factors to consider before you purchase a turbo as well, like do I have enough room in my engine bay? A lot of modern vehicles lack adequate space under the hood for a turbo, and with the majority of today’s parts being made from plastic, there can be a serious meltdown and fire risk. A great alternative is to use mid or even rear mounted turbos from companies like STS. The turbos can be installed near the rear of your vehicle, freeing up space and also offering some added cooling benefits as well.
Yes, size does matter! Both under-turboing and over-turboing can create headaches like turbo lag, over boost and compressor surge. A popular rule of thumb is to pick a turbo with the smallest wheel diameter possible, that still allows you to meet your horsepower goals. I won’t bore you with the math that’s involved in determining ideal A/R ratios, but if you’re considering a turbo purchase, it’s a good idea to speak with a reputable turbo company first. Provide them all the information possible about your particular set-up so they can recommend the best turbo for your application. They can also help you size the correct wastegate to prevent over-boost and suggest a blow-off valve to prevent compressor damage.
Selecting a turbo is a lot like life, the more educated you are the better off you’ll be.
For more information on our full line of STS turbos or to get a recommendation for your ride, visit our website at STS turbochargers.com
Rick Seitz is the owner and founder of Blue Oval Muscle Magazine, and has a true love and passion for all vehicles. When he isn’t tuning, testing, or competing with the brand’s current crop of project vehicles, he’s busy tinkering and planning the next modifications for his own cars.