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Have you ever wondered how compound turbos work?

Have you ever wondered how compound turbos work?

Posted by Diesel Power Source on Jan 29, 2024

Here is an inside look at the operation of compound turbos.

Compound turbos, also known as sequential systems, utilize a small turbo that spools up quickly and supplies the engine with air until a larger turbo has the time to spool up and engage. This process provides substantial amounts of air while simultaneously alleviating turbo lag. So, here's how it works. The air filter allows air to enter either the S400 turbo, which is significantly larger than the S300 or small turbo.

We typically use a 75-millimeter wheel (an S475), an 80-millimeter wheel (an S480), or an 83-millimeter wheel as the primary turbo to pressurize the secondary turbo, which usually features a 62, 63, 64, 66, or 69-millimeter compressor wheel. We also offer an add-a-turbo option where a large S475 turbo pressurizes a small stock turbo. On the air or cool side, air enters the 1st turbo (the primary or large turbo), pressurizing the air and turbocharging the second turbo. Essentially, the first turbo takes in air at atmospheric pressure and pressurizes it around 2 to 2.5 times into the second turbo.

In the 2nd Turbo, this air is then further pressurized and multiplied by two to 2 to 2.5 times, and the highly compressed air is pushed through the other charge pipe into the intercooler and then into the engine. The exhaust, on the other hand, exits the engine, goes through the exhaust manifold, enters the hot side of the small turbo (the turbine or exhaust housing), where it is piped over, turns the turbine or exhaust wheel, and is then channeled through the cast iron hot pipe into the exhaust housing of the large turbo, causing the exhaust wheel to turn. The exhaust is then expelled through the downpipe and out of the truck. Turbine wheels are connected to the compressor wheels or impellers on the other side of the turbo. As the exhaust goes over the turbine wheel, it also causes the compressor wheel to spin, sucking in air and compressing it through the system on the cold side, as discussed earlier. This is what enables the quick spool-up of a compound turbo kit.

In a compound turbo system, air goes into the big turbo first, followed by the small turbo. The exhaust goes into the small turbo first, followed by the large turbo. This is analogous to the compressors and turbines in a jet engine, where the atmospheric compressors are always the large ones, and the secondary set of compressors are the smaller ones. In a jet engine, the exhaust passes through the smaller turbines first and then exits into the larger turbines. The benefits of this system are significant because it not only compresses enough air to burn all the fuel in the cylinders but also adds additional air that carries away heat. By doing this, our compounds can lower EGTs by 300-400 degrees and drastically clean up the exhaust. Our compounds also balance drive pressures to boost pressures, providing power on the intake stroke.

DPS Compounds are designed as bolt-on applications that keep your truck drivable while delivering incredible results, such as increasing horsepower by approximately 25%, cleaning up black smoke, reducing EGTs to the point they become a non-issue, even when towing up a long steep grade with a heavy load at speeds exceeding 70 mph, and protecting your engine from sticking a piston.

Here at Diesel Power Source, we have been manufacturing the best direct bolt-on compound kits for over 18 years now and would be happy to answer any questions you may have.