300+ BHP Abarth 500 Demo Build – Part 2

GBC 20-300 Turbo, GMC Racing Tubular Manifold & ARP Head Studs

Welcome to Part 2 of our 300+ BHP Abarth 500 demo car build series.

In Part 1, we focused on putting the power to the ground with the installation of a Prometeo Limited Slip Differential.

Now the attention moves to the engine itself.

Our partners at ADEdmundson have continued with the build, and some of the most important components for our new 300+ BHP setup are now being installed.

For this stage we have chosen a GBC 20-300 turbocharger, GMC Racing tubular exhaust manifold and downpipe kit, together with an ARP M9 uprated head stud and nut kit.

This combination forms a major part of the hardware package that we will use to develop and test the next generation of TMC Motorsport Abarth turbo kits.

Moving Beyond Our Existing 285 BHP Packages

For many years, our turbo packages up to approximately 285 BHP have been some of the most popular tried-and-tested options we offer for the Abarth 500, 595 and 695 platform.

With this car, we want to take the next step.

The aim is not simply to bolt on a larger turbo and chase a dyno figure. We want to develop a complete package capable of producing 300 BHP and beyond, while still focusing on reliability, driveability and repeatable performance.

That means looking at the complete system around the turbo, including exhaust flow, cylinder head clamping, cooling, fuelling, engine internals and ultimately the calibration.

Part 2 deals with three particularly important pieces of that puzzle.

GBC 20-300 Turbocharger

At the centre of the new setup is the GBC 20-300 turbocharger.

The 20-300 gives us the airflow capacity needed to move into the next performance bracket while remaining suited to the characteristics of the Abarth 1.4 T-Jet engine.

Rather than simply fitting the largest turbo possible, the objective with this car is to develop a combination that provides strong top-end performance without completely sacrificing response and usability.

That balance will be particularly important when we begin mapping and road testing the car.

The 20-300 also gives us room to properly evaluate the supporting components around it and determine exactly how we want to structure our forthcoming TMC 300+ BHP turbo packages.

GMC Racing Tubular Manifold

The turbo is being paired with a GMC Racing tubular exhaust manifold.

Once airflow requirements increase, the exhaust manifold becomes a significant part of the overall turbo system.

A tubular manifold is designed to improve the route exhaust gases take from the cylinder head into the turbine housing, reducing the restrictions associated with the standard cast manifold arrangement.

Improved exhaust gas flow helps the turbocharger operate more efficiently and becomes increasingly important as boost pressure, airflow and engine speed increase.

For a build targeting more than 300 BHP, we wanted the exhaust side of the engine to be designed around the increased airflow requirements rather than allowing the original manifold to become a restriction.

And frankly, it also happens to look considerably more interesting than a lump of factory cast iron, which is a rare occasion where engineering and aesthetics agree with each other.

GMC Racing Downpipe

The matching GMC Racing downpipe completes the hot side of the turbo setup.

The downpipe is responsible for allowing exhaust gases to leave the turbine housing efficiently.

As turbocharger size and airflow increase, reducing unnecessary restriction after the turbine becomes increasingly important.

The GMC Racing manifold and downpipe therefore work together as a complete system, allowing us to optimise exhaust flow both into and out of the GBC turbocharger.

This will become particularly important once ADEdmundson begin calibration and we start assessing boost response, exhaust gas flow and overall performance.

ARP M9 Uprated Head Studs & Nuts

While the turbo and tubular manifold naturally attract most of the attention, the ARP M9 uprated head studs and nuts are arguably one of the more important reliability upgrades in this stage of the build.

Increasing boost increases cylinder pressure.

That places additional load on the cylinder head, head gasket and the fasteners responsible for clamping the cylinder head to the block.

The purpose of the uprated ARP stud arrangement is to provide stronger and more consistent cylinder head clamping than the standard fastening system.

Maintaining that clamping force becomes increasingly important as cylinder pressures rise.

On a higher-output 1.4 T-Jet build, improved head clamping helps reduce the potential for movement between the cylinder head and block under heavy load and provides additional security as we begin pushing the engine beyond the output levels of our existing turbo packages.

It is exactly the type of upgrade that may not make any additional horsepower on its own, but helps make that horsepower significantly safer to use.

Building the Engine Around the Power Target

One of the key principles behind this project is that the engine is being built around the intended power level rather than simply increasing boost until something complains.

Alongside the components covered in this instalment, the engine specification will include forged internals and further supporting upgrades before final calibration begins.

Every component is being selected with the complete package in mind.

The turbo needs sufficient airflow.

The manifold and downpipe need to support that airflow.

The engine needs to withstand the additional cylinder pressure.

The drivetrain needs to transfer the torque to the road.

And the calibration ultimately needs to bring all of those elements together.

That is the approach we are taking with this car.

Why We Haven’t Fitted an Enlarged Oil Sump

One thing you may have noticed is that we haven’t included an enlarged Prometeo oil sump in the build.

That was a deliberate decision.

This car was never intended to become a full-on track car. The goal from the beginning has been to build a very capable fast-road Abarth, with enough supporting hardware to handle the occasional track day without compromising how usable the car is on the road.

For that reason, we didn’t feel an enlarged-capacity sump was necessary for the intended use of this particular build.

An enlarged sump can absolutely make sense on cars that are going to see sustained high-load track use, where additional oil capacity and temperature control become more important. But for a road-focused car that may only see occasional circuit use, we felt the standard sump arrangement was appropriate for the brief.

That is really the philosophy behind this whole project.

We are not fitting parts simply because they exist or because they appear on every high-powered build. Each component is being chosen based on what the car actually needs for its intended use.

The result should be a 300+ BHP Abarth that remains usable, responsive and enjoyable on the road, while still being more than capable of handling the occasional track day.

Built in Partnership with ADEdmundson

As with the differential installation covered in Part 1, the engine build and assembly work is being carried out by ADEdmundson.

Their experience with heavily modified 1.4 T-Jet engines makes them the ideal partner for the development programme, particularly as they currently operate the UK's fastest 1.4 T-Jet.

The knowledge gained during the build, calibration and testing of this car will feed directly into the development of our upcoming TMC Motorsport turbo packages.

What’s Next?

With the GBC 20-300 turbo, GMC Racing manifold and downpipe, and ARP head studs now forming part of the engine specification, the foundations of the new turbo setup are starting to take shape.

There is still plenty to come.

The next stages of the series will cover more of the internal engine specification, supporting hardware, cooling upgrades, induction setup and eventually the mapping and testing process.

And, naturally, the bit everyone will eventually scroll directly towards regardless of how much technical information we write beforehand:

The dyno results.

Stay tuned for Part 3 of our 300+ BHP Abarth 500 Demo Build.