Can a 1.9-litre diesel engine produce 250 horsepower? This Saab 1.9 TTiD TwinTurbo project at AUTOCHIP demonstrates what can be achieved by combining upgraded turbocharger hardware with a carefully developed ECU calibration.

The owner had previously fitted hybrid turbochargers, and the car already had a history of Stage 1 tuning. Our task was to develop a custom Stage 2 calibration suitable for the upgraded hardware, analyse engine operating data and measure the resulting performance.

The project achieved 250 hp and 480 Nm of torque. During the assessment, we also identified an intake system restriction that should be addressed before attempting further power increases.

Saab 1.9 TTiD — a 180 hp twin-turbo diesel

This Saab uses a 1.9-litre diesel engine with a twin-turbocharger arrangement. The engine family shares technical heritage with diesel powertrains also used in Opel vehicles.

The factory-rated output of this version was 180 hp. However, the car had already undergone tuning before the Stage 2 project began.

With its earlier Stage 1 calibration and before the installation of hybrid turbochargers, the Saab had produced 207 hp and 430 Nm during dynamometer testing.

The owner subsequently upgraded the turbochargers and brought the car to AUTOCHIP for a calibration that could make use of the new hardware.

The vehicle's emissions control equipment had already been removed before this work. Those earlier modifications were not carried out as part of the Stage 2 calibration shown in the video. Such a configuration may not meet the requirements for public-road use.

What do hybrid turbochargers change?

A hybrid turbocharger is a modified turbocharger that may incorporate different compressor or turbine wheels, revised internal geometry or other upgraded components.

Depending on the design, these changes can increase airflow capability or alter how the turbocharger performs across the engine's operating range.

For a diesel engine, greater airflow capacity can help support increased fuel delivery and higher power output. However, fitting hybrid turbos does not automatically guarantee more horsepower.

The engine management system must be calibrated to work with the updated turbochargers, while the fuel system, intake components and other hardware must be capable of supporting the desired operating conditions.

This is why Stage 2 tuning requires attention to more than peak boost pressure. Torque management, fuel injection, turbocharger control and engine protection strategies all need to be considered together.

Stage 1 versus Stage 2 — dyno results

This Saab provides a useful comparison between its earlier Stage 1 setup and the configuration developed after the hybrid turbocharger upgrade.

Performance figures reported in the video:

• Factory-rated power: 180 hp.
• Previous Stage 1 without hybrid turbos: 207 hp and 430 Nm.
• Stage 2 with hybrid turbos: 250 hp and 480 Nm achieved.

Compared with the previous Stage 1 results, the Stage 2 configuration delivered an increase of 43 hp and 50 Nm.

It is important to note that this improvement reflects both the upgraded turbochargers and the revised ECU calibration. It would be incorrect to attribute the entire gain to software changes alone.

During subsequent dynamometer testing, one repeat run produced approximately 10 hp and 9 Nm less than the earlier reported result. The technician attributed the reduction to elevated temperatures during testing.

An unexpected limitation: the collapsing intake hose

One of the most interesting findings in this project had nothing to do with the ECU software itself.

During the inspection, the AUTOCHIP technician demonstrated a flexible intake hose that could deform and collapse under the vacuum generated as the turbochargers drew air through the intake system.

When an intake hose collapses, its effective internal cross-section becomes smaller, restricting airflow. This can limit the amount of air available to the turbochargers and reduce the benefit of upgraded compressor hardware.

The problem becomes particularly relevant when an engine has been modified to demand more air than its original intake arrangement was designed to supply.

For this Saab, the technician recommended replacing or redesigning the affected intake section with stronger, appropriately sized piping that could maintain its shape under operating conditions.

This was identified as a necessary future improvement. The video does not confirm that the intake piping had already been replaced.

Would a high-flow air filter help?

Alongside the intake piping, the technician discussed installing a high-flow air filter to reduce restrictions in the air supply system.

At the time of filming, the proposed filter had not been installed. It was considered a possible addition to the planned intake improvements.

However, a high-flow filter should not be selected on airflow capacity alone. Filtration efficiency, protection against dust, air intake temperature and suitability for the intended operating conditions are equally important.

Even products described as zero-resistance filters still create some airflow resistance. The objective is to achieve a suitable balance between airflow and effective engine protection.

For this reason, the complete intake system should be evaluated rather than assuming that a filter change alone will produce a measurable horsepower increase.

Fuel rail pressure — why an upgraded sensor was not installed

Another interesting decision involved the diesel fuel system.

An alternative Common Rail pressure sensor with a higher measurement range had been considered for the project.

However, after reviewing the relevant engine operating data, the technician concluded that the existing fuel rail pressure control range was sufficient for the current Stage 2 configuration.

As a result, the additional rail pressure sensor was not installed.

This is an important principle of professional tuning. Installing a component with a greater measurement range does not automatically improve engine performance if the existing equipment already meets the requirements.

A rail pressure sensor measures pressure; it does not increase the fuel delivery capacity of the high-pressure pump or injectors. The entire fuel system must be assessed before pursuing higher pressure or additional fuel delivery.

For this Saab, the current setup was considered adequate. The possibility of revisiting the sensor and fuel system configuration was left open for any future performance development.

Custom Stage 2 tuning with ECU data logging

Developing the calibration involved more than editing an ECU file and performing a single power run.

AUTOCHIP examined engine data logs, including temperature information, requested versus actual operating parameters and fuel rail pressure behaviour.

This type of analysis is particularly important with modified diesel engines because the final power figure does not reveal how effectively each component is operating.

For example, comparing requested and actual rail pressure helps determine whether the fuel system can consistently follow the ECU's commands under the tested conditions.

Likewise, reviewing temperature and boost-related information can help identify restrictions or operating conditions that might not be obvious from peak horsepower alone.

The objective was to develop a calibration that worked with the vehicle's existing hardware rather than adding modifications without a demonstrated need.

How did high temperatures affect the dyno runs?

The dynamometer testing took place in hot conditions. The workshop temperature was approximately 29–30°C, with similarly warm weather outside.

During repeated high-load runs, the engine, intake air and surrounding components can accumulate heat. Higher temperatures may influence available power, particularly on turbocharged engines.

During one later dyno run, the Saab produced approximately 10 hp and 9 Nm less than the previously achieved figures.

The technician associated this difference with the elevated temperatures during testing. The video does not establish a separate long-term assessment of the cause, but heat accumulation is a relevant consideration when comparing repeated dynamometer results.

This also demonstrates why professional performance evaluation should consider operating conditions and repeatability rather than relying exclusively on the highest number recorded during a session.

Relocating the ECU to protect it from moisture

The Saab also featured an interesting modification to the location of its engine control unit.

According to the technician, the original ECU location was relatively low in the wheel arch area, where exposure to water, road salt and dirt could become a concern.

The owner had already relocated the control unit to a higher position in an effort to reduce exposure to these conditions.

Such a modification may help protect the ECU from environmental damage, provided that the wiring, connectors, mounting and vibration protection remain suitable.

Importantly, this relocation had been completed by the owner before the Stage 2 work. It was not part of the ECU calibration carried out by AUTOCHIP in the video.

Is there potential for more than 250 hp?

The achieved output of 250 hp and 480 Nm is an impressive result for a 1.9-litre twin-turbo diesel engine.

Nevertheless, the technician identified further improvements worth considering before pursuing additional power.

The main priority was the intake system, particularly replacing the flexible hose that could restrict airflow under load.

After suitable mechanical changes, the vehicle could be tested again and its ECU calibration reassessed to determine whether further improvements are practical.

However, no additional horsepower gain from the proposed intake modifications has been verified. The upgraded piping and air filter were still future plans at the time of filming.

The technician considered the current calibration suitable for everyday driving, but the video does not document extended durability testing. Long-term reliability would depend on the mechanical condition of the engine, turbochargers, transmission and other supporting components.

Saab Stage 2 ECU tuning at AUTOCHIP

This Saab 1.9 TTiD TwinTurbo project illustrates how hybrid turbochargers, custom ECU calibration and detailed diagnostics can work together to improve diesel engine performance.

The main result was 250 hp and 480 Nm, compared with the earlier Stage 1 figures of 207 hp and 430 Nm before the hybrid turbocharger upgrade.

Equally important was identifying the intake restriction and deciding that a higher-range Common Rail pressure sensor was unnecessary for the existing configuration.

AUTOCHIP provides custom Stage 1 and Stage 2 ECU tuning, vehicle diagnostics, data logging and dynamometer testing. Each project is assessed according to the vehicle's actual hardware configuration and mechanical capabilities.

Watch the accompanying video for a closer look at the Saab's dyno performance, intake system limitations and the technical decisions made during its Stage 2 calibration.