Parallel Sequential Turbocharger Installation

 In Turbochargers

How does Parallel Sequential turbo work?

Sequential turbo set-ups feature one small and one large turbocharger. The small turbo mainly boosts low speeds, and the larger one is for higher engine speeds. The limited exhaust gas is directed into the smaller turbocharger when engine speed is low, resulting in rapid boost production. Although, it can only happen if a prompt response to the driver’s accelerator input and improved engine output is there.

Further, the engine management system is responsible for bringing the second turbocharger online as the power demands and engine speed increase. The exhaust gas will redirect into the second turbocharger, and this gas will start spooling even before it’s called on in earnest. This function is there to avoid erratic changes in engine output.

The engine’s exhaust can be diverted into the large turbocharger as the second turbo gains speed, reaching its maximum output. Depending on the system’s configuration, valves on the intake side may also open and close to the respective turbochargers to avoid pressurized air escaping through the bypassed turbocharger.

When the first turbocharger continues to be used throughout the entire rev range, this particular arrangement is called parallel-sequential turbocharging. It might also interest you that, when one turbocharger is bypassed and the second one is introduced, the set-up is known as series-sequential configuration.

We’re quite sure that the sequential turbo system and the parallel-sequential turbo system must have caught your eye by now. Let’s know more about them.

Sequential Turbocharger

In Sequential Turbo, there are two different sizes of turbochargers. The small one is a vaned turbo for low exhaust gas flow at lower engine speeds. And a much larger second turbo is for taking over once it’s had a chance to spool up.

Further, the main function of a sequential Turbo that sits in front of the larger turbo is to ensure that all low-energy exhaust gasses produced at the bottom end of the rev range get isolated and go straight to the smaller turbocharger. This compression valve renders most single turbocharger set-ups useless and maximizes power delivery at a rev range once useless to most. 

On top of that, this valve is triggered to open fully at a set airflow volume, and it’ll only be opened slightly as the engine speed rises. It allows the larger turbine to spool and the secondary turbo to be efficient.

Thus, sequential turbo single-handedly takes away almost all the downsides of single turbocharging. That way, it also supersedes a parallel set-up as the secondary turbo is set to extremely high boost and relies on the primary turbo to get rid of any lag lower down. 

Modifying your vehicle

If you’re interested in modifying your vehicle, your car modifier can get pretty crazy with a sequential turbocharger and can vary the ratio between the small & large turbos to create some unbelievable power. Think of a midsize sedan to visualize the greatest possible platform for sequential turbo.

Further, in sequential Turbo Charging, the two turbos are different sizes. The small turbo is used in the low RPM scenarios when the exhaust gas flow is low and smaller in size, and it does not need too much flow for the turbine to rotate. Therefore, it’s effective in eliminating the low-end turbo-lag. 

The turbocharger can reach its mechanical limitations once the RPMs are high enough. In that case, the operation is shifted to the bigger turbocharger, and the bigger turbocharger keeps the boost going during the mid RPM range. 

You can only find this complex mechanism or construction in high-end luxury and performance cars, so if there’s a very high RPM, these turbos can simultaneously work to maximize the boost. The main advantage of a sequential turbo is that it covers an extremely wide range of RPM.

Parallel Turbocharging

The parallel arrangement of the two turbos or parallel turbocharging comes into the picture when more cylinders with two-cylinder banks such as V8, V10, or V12 are there. Managing the turbo and intake manifold connections with too many cylinders attached to the same turbo becomes increasingly difficult. And that is why two turbos are connected to the two-cylinder banks; hence the same function is achieved.

Now, using two turbochargers of the same size together to force air as fast as possible into the cylinders is what you would call classic yet standard twin turbocharging. When recycled to the turbos, the exhaust gasses are equally split. Generally, they’ll combine again in a common inlet before entering the cylinders again.

Advantages of Parallel Sequential Turbocharger

The main advantage of a parallel turbo is the potential for much less turbo lag. This benefit makes parallel turbos great compared to one large turbocharger doing all the work. A turbo is usually assigned its bank of cylinders in V-engines instead of a single large one. It is done to force air through convoluted plumbing and make its way through the engine bay to the required cylinders. 

Also, there can be a lack of lag in parallel turbocharging. Why? Well, it’s mainly due to the convention of using slightly smaller turbos when parallel twin-turbocharging. Apart from that, one large turbo is replaced with larger vanes, making the spooling process quite simple for the incoming air.

Power parallel turbos should be set at relatively low boost pressure to reduce turbo lag to keep these benefits while balancing. Don’t worry; the combination of the two turbines will still create ample power.

Benefits for Two-Stage Parallel Sequential Turbocharger for Diesel Engines:

Sequential Turbocharger turbocharger detailed view

The high-performance two-stage parallel-sequential turbo for diesel engines has several benefits, including:

  • Highly improved vehicle acceleration, power as well as torque compared with similar diesel engines
  • Superior transient behavior produces a longer gear ratio strategy
  • Reduced fuel consumption and raw emissions
  • Lowered after-treatment complexity and cost
  • Low thermal inertia produces the same catalyst light-off
    speed as single turbos

Sequential Turbocharger Repair Services

At Diesel Components Inc., we have the right parts and the right people with up-to-date training to handle all your sequential turbo repair maintenance requirements. The knowledge gained from repairing all kinds of turbochargers has enhanced our performance. 

When other repair companies may entice you with a lower price, Diesel Components, Inc. does not cut corners when it comes to parallel-sequential turbo repair services.

As a factory-authorized repair facility, rest assured, we’ll always use top-quality parts and the latest repair techniques as we believe in doing the job right the first time. Contact us to get your turbocharger today!

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