TDI120: My New Engine

timmus

A2OC Donor
Four years ago, with 156,000 miles on the clock, I started needing to top up my car’s coolant every ten days or so. The conclusion was that my cylinder head gasket had gone. I think I was unlucky, because this isn’t a common problem with the 1.4 TDI. In replacing the head gasket, it was noticed that the turbo was dripping a bit of oil; nothing serious, but enough to get me thinking about its eventual replacement. Never content to do a simple replacement without looking into other options, I started to research and found that I had an opportunity to make some improvements. As time progressed, this thought process got a little out of control and gave rise to a project much bigger than I had originally intended.

Various upgrades to the turbo turned out to be possible, but doing so would also require improvements to an assortment of other engine components. At this time, my intention was to assemble a collection of improved components and fit them to my existing engine. However, part way through this process, a message from Sarge changed the game. In early 2014, Sarge acquired a brand new 1.4 TDI; just the core engine, without any ancillaries. His intention was to fit it to one of his A2s, but life got in the way and he eventually decided that it was a project that would never reach the top of his priority list. I am hugely grateful to him for offering the engine to me. My original plan to upgrade my existing engine changed in an instant. Here was a unique opportunity to wind back the years and to create something really special: my ultimate 1.4 TDI.

For me, the ultimate 1.4 TDI comes from maximising all its existing qualities. It’s about bulletproof reliability, efficiency and refinement as well as an ability to thrill. If maximising output power sacrifices reliability, then the overall engine has been skewed in favour of one characteristic over another rather than having its improvements in balance.

From factory, the 1.4 TDI came in two basic configurations: 75bhp and 90bhp. Both can be tuned by means of a software remap without any physical modifications, with the TDI75 thereby achieving 95-105bhp and the TDI90 achieving 110-120bhp. Whilst both are very good engines, the consensus is that the TDI75 is the more reliable and the more frugal, albeit not by much. A remapped TDI90 is a lot of fun, but the extra power comes at the expense of simplicity and reliability, its turbo and flywheel designs being the documented weaknesses. In creating my ultimate 1.4 TDI, the goal was to get the best of both worlds. I wanted to create an engine with a split personality; a Jekyll and Hyde machine capable of top-drawer fuel efficiency but with the power to be exhilarating when desired.
However, to keep within my OEM philosophy, everything had to fit as standard. No fettling of parts from other VAG Group vehicles was permitted. Instead, methods had to be found to improve the design of the original A2 components. My engine and its installation had to retain all the character of the original.

In this thread, I hope to explain, in a manner that’s accessible to all, how this goal was achieved. There’s a lot to read, but I’ve broken the project down into sections, so there’s no need to read it all at once. I hope it proves to be interesting. Those who are already well versed in the principles and inner workings of VAG diesels may wish to skim read certain sections.
 
Last edited:

timmus

A2OC Donor
2. TDI Basics

TDI stands for Turbocharged Direct Injection and refers to the way in which air and fuel are delivered to the combustion chamber. In order for an internal combustion engine to run, two chemical reagents are required: fuel and oxygen. Their reaction releases energy, which turns the engine and moves the vehicle. If the quantity of either one of these reagents is limited, the power output of the engine is also limited. Power output can only be increased by making larger quantities of both reagents available; thus injecting more fuel cannot release more power unless there is also sufficient oxygen in which to burn it.
The name TDI is an acronym derived from the way in which the engine supplies itself with oxygen and fuel.

The ‘T’: Supplying oxygen through forced induction
When the piston in an engine moves downwards in its cylinder, air rushes into the cylinder to fill the void. The quantity of air that fills the cylinder is called the charge. This process is a mechanical analogue of human breathing; as the diaphragm moves downwards, air rushes in to take up the space that’s been created inside the ribcage, thus filling the lungs with a ‘charge’ of air. Conventionally, atmospheric pressure outside the engine is the force that causes the air to fill the cylinder. Once the air pressure inside the cylinder has reached atmospheric pressure, no more air will enter, thus limiting the amount of oxygen available for burning fuel. Engines that work on this principle are referred to as naturally aspirated. Both the 1.6 FSI and 1.4 petrol engines available in the A2 are naturally aspirated.
More air can be forced into the cylinder by using a pump, allowing more fuel to be burnt and therefore more power to be produced than when relying on atmospheric pressure alone. Engines that use a pump to fill the cylinders with air are referred to as forced induction. The pump is able to create a much denser charge of air containing much more oxygen: a supercharge! The pump is therefore called a supercharger. A supercharger is an air compressor that increases the density of air supplied to each cylinder with every rotation of the engine. More air means more fuel burnt and more power produced.
However, something has to drive the air compressor. A conventional supercharger is driven mechanically by the engine, usually by means of a belt or chain. As the engine rotates, it drives the supercharger as well as the car itself. Unfortunately, this means that the supercharger is a parasite, stealing some of the engine’s output power for itself and thus decreasing fuel economy. The solution to this problem is instead to power the supercharger by introducing a turbine into the flow of exhaust gas. As exhaust exits the engine, it spins the turbine which in turn drives the supercharger. A supercharger that is driven by the flow of exhaust gas is called a turbosupercharger, or just turbo for short. All diesel A2s are fitted with a turbo, hence the ‘T’ in TDI. Improving the turbo’s ability to deliver large quantities of oxygen to the engine is a major aspect of this project, as discussed later.

The ‘DI’: Supplying fuel by direct injection
Once the cylinder is filled with air, the piston moves upwards, squeezing the charge of air into a tiny space at the top of the cylinder. At just the right moment, the fuel is injected under immense pressure into the cylinder. The fuel reacts with the oxygen in the air, causing an explosion that forces the piston back down again, thus turning the engine and driving the car forwards. This technique of introducing the fuel directly into a cylinder of highly compressed air is called direct injection, hence the ‘DI’ in TDI. Of the engines available in the A2, only the 1.4 petrol is not direct injection. Increasing the amount of fuel that can be injected into the cylinder with each cycle of the engine was another essential part of my project. Practically, however, increasing the supply of oxygen is by far the greater challenge, so much of this thread is dedicated to how this was achieved.
 
Last edited:

timmus

A2OC Donor
3. The Core Engine

Fig. 3.1 and 3.2 show all sides of the core engine, as collected from Sarge. It is a standard 3-cylinder 1.4 TDI, ready assembled by Audi themselves. It’ll be the base for everything else. It’s brand new with zero miles on the clock.

Fig. 3.1
3.1 - Core Engine Sides.jpg


Fig. 3.2
3.2 - Core Engine Faces.jpg

The selection of this core engine was determined by two factors. The first was simple availability (it was the only brand new engine on offer to me!) and the second was my active preference for the variant of core engine that favours fuel efficiency. The core of the 1.4 TDI was available in two flavours; one for the TDI75 and one for the TDI90. The only difference is their compression ratio; that is the ratio of the maximum volume of the cylinder to the minimum volume of the cylinder. The TDI90 has a compression ratio of 18:1, meaning the cylinder is 18 times smaller when the piston is at its highest point than when the piston is at its lowest point. The TDI75, on the other hand, has a compression ratio of 19.5:1, meaning the charge of air is squeezed more. As a general rule, higher compression ratios result in greater efficiency. Given that greater performance can be derived from improved ancillaries, such as the turbo, the TDI75 core was my choice.

There are all manner of modifications that could have been made to the internal components of the core engine. Despite this, I have chosen not to modify it at all because the design has, in either TDI75 or TDI90 guise, already proved itself capable of all the qualities I’m looking to attain. Even with my inclination to tweak things, there are areas where I decide to let the don’t-fix-what-isn’t-broken rule apply.

Core Engine Basics
Fig. 3.3 shows the core engine with some basic annotation. For those who are new to the workings of the core engine, a familiarity with some terms will assist in following several later sections of this article.

Fig. 3.3
3.3 - Annotated.jpg

The block is the part in which the pistons move up and down. As the pistons move, they turn the crankshaft, the rotation of which is ultimately what drives the car. The cylinder head houses the fuel injectors as well as the valves that allow air and exhaust gas to enter and exit the cylinders. The rotation of the camshaft governs the timing of the engine; when air is allowed to enter the cylinder, when exhaust gasses are allowed out and when fuel in injected. The rocker cover is simply the engine’s lid. The sump houses a pool of oil, which is continuously pumped around the engine whilst it is running.
 
Last edited:

timmus

A2OC Donor
4. The Turbo

As previously mentioned, a turbo is a pump that uses the flow of exhaust gas to drive a compressor. Fig. 4.1 is an annotated graphic showing the standard turbo from the AMF engine (earlier TDI75).

Fig. 4.1
4.1 - How Turbo Works.jpg

Hot exhaust gasses exit the core engine from each of the three cylinders, marked C1, C2 and C3. The gasses combine in the exhaust manifold, marked EM, and then collect in the turbine housing. As the gas escapes into the exhaust pipe, marked EP, it spins the turbine (essentially a small windmill). The turbine is connected via a rotating shaft to the compressor wheel (another small windmill). As such, as soon as the turbine starts spinning, so does the compressor wheel. The rotation of the compressor wheel draws fresh air from the atmosphere, marked A, and compresses it, creating pressurised air (referred to as ‘boost’) at P. This pressurised air contains large quantities of oxygen, ready to burn fuel. Once the pressurised air has been used to burn fuel, it becomes the exhaust gas that drives the turbine, thus compressing more fresh air and keeping the process going.

However, getting this process started isn’t straightforward. When the engine is at idle, it doesn’t produce enough exhaust gas to properly spin the turbine. Without a spinning turbine, there’s no spinning compressor and therefore no boost. In essence, the turbo is a highly ineffective supercharger when the engine is at low revs. Consequently, when getting going from idle, the engine is reliant upon atmospheric pressure to deliver oxygen to the cylinders. As engine revs build, more and more exhaust gas is emitted, causing the turbine to spin and the compressor to create boost. Once boost has been created, more fuel can be burnt with each cycle of the engine and therefore much more power is generated. This delay between first pressing the accelerator and the delivery of appreciable power is called turbo lag. Most drivers of the A2 TDI will be familiar with the phenomenon.

The ideal turbo would be able to deliver lots of boost very quickly, thus causing the engine to generate lots of power with as little turbo lag as possible. However, a number of engineering trade-offs exist that must be finely balanced in order to create a turbo that is as suitable for its application as possible. Below are the explanations of the changes that have been made to the standard design.

The Exhaust Manifold

Fig. 4.2
4.2 - Exhaust Manifold.jpg

The exhaust manifold combines the exhaust gas emitted from each of the engine’s three cylinders into one flow of gas. Comparing Fig. 4.1 and 4.2, the most obvious change is the design of the exhaust manifold.
Whereas the turbo from the AMF engine (earlier TDI75) has its exhaust manifold and turbine housing as separate parts that bolt together, the turbo from the BHC engine (later TDI75) has its exhaust manifold and turbine housing combined into one part. This combination part is designed to optimise the smooth flow of exhaust gas through the turbine.
When an engine starts its exhaust stroke, the piston moves up the cylinder, causing high pressure exhaust gas to escape into the exhaust manifold, creating an 'exhaust pulse'. Exhaust gas is emitted from the three cylinders of the 1.4 TDI in a sequence of pulses. Notice that the distances from each of the exhaust ports to the centre line of the turbine housing is a multiple of d. As such, as the exhaust pulses travel along the manifold, they mesh together perfectly, like a 3-sided zip, creating a single, smooth flow. The left-hand and right-hand branches of the exhaust manifold are curved at the centre line towards the turbine housing, further aiding smooth flow. This smooth flow helps to get the turbine spinning sooner, resulting in reduced turbo lag.

Another noticeable difference between the two exhaust manifold designs is the positioning of the EGR output. This will be discussed later.

The Turbine

Fig. 4.3
4.3 - Turbine Angle.jpg

Fig. 4.3 shows the turbo from a different angle, allowing the turbine to be seen. For ease of orientation, its annotation is consistent with Fig. 4.1. The exhaust from the manifold arrives behind the turbine and finds that its only means of escape is to flow through the turbine, thus causing it to spin.

Looking more closely at the turbine itself reveals that the profile of the individual turbine blades has been modified, using a technique called cut-back, shown in Fig. 4.4 below. Cut-back of the turbine blades involves cutting away a tiny bit of metal from the tips of the blades, introducing a slight angle of roughly 7 to 10 degrees to the trailing edges of the blades. This reduces the amount of metal that is in the path of the exhaust gas, thereby lowering the resistance that the turbine presents to the exhaust gas flowing through it.

Fig. 4.4
4.4 - Turbine Cut-Back.jpg

Allowing the exhaust gas to escape more quickly increases engine power once the turbine is up to speed. However, because the turbine blades are now fractionally smaller, the turbine takes longer to build speed when there’s low exhaust flow. As such, the trade-off for increased power at high RPM is a slight increase in turbo lag.

The wastegate, shown in Fig. 4.3, provides a secondary route for exhaust gas to flow from the turbine housing into the exhaust pipe, thus bypassing the turbine. Should the turbine be at risk of spinning too fast, potentially causing catastrophic failure, the wastegate opens. As the wastegate is controlled by the engine management unit, it allows the amount of boost generated by the turbo to be precisely controlled.

The Compressor Wheel

As the turbine spins, so does the compressor wheel. The rotation of the compressor wheel draws air from the atmosphere and compresses it, like a rotary version of a bicycle pump. Just as a larger bicycle pump compresses more air per stroke than a smaller pump, a larger compressor wheel compresses more air per rotation. Fig. 4.5 shows the original compressor wheel on the left and the new compressor wheel on the right.

Fig. 4.5
4.5 - Compressor Comparison.jpg

The original compressor wheel is made from cast aluminium, where molten aluminium is poured into a mould. As the molten aluminium solidifies, the individual atoms come to rest in a haphazard manner, resulting in a metal that is very porous, filled with tiny air bubbles and doesn’t have very consistent density throughout the material. Internally, its texture is very grainy, meaning it gets brittle when thin. As such, there’s a limit to how fine the individual blades of the compressor wheel can be made.
The modified compressor wheel is machined from billet aluminium. Billet aluminium is made by pouring impurity-free molten aluminium into a simple form under immense pressure. The high pressure removes all traces of air and causes the individual atoms to align, resulting in a solid block of aluminium that has no grain and is effectively a single, massive molecule of aluminium. The compressor wheel is then made by cutting away the unwanted material. Due to its strength, the blades of the compressor wheel can be made much thinner, thus reducing weight. Consequently, the new compressor wheel is 25% larger than standard but, crucially, its total mass is no greater.

Keeping compressor wheel mass to a minimum is important due to rotational inertia. The greater the mass of the compressor wheel and the greater the distribution of that mass towards the outside edge, the more rotational inertia the compressor wheel has and the more energy is therefore needed to get it spinning. This is analogous to a playground roundabout that’s being spun by someone stood on the ground. Without any children on the roundabout, its mass is low and it is therefore easily spun without a great deal of energy expenditure. As children climb onto the roundabout, total mass increases. If the children stand close to the centre of the roundabout (close to the axis of rotation), total rotational inertia increases only slightly and therefore only a small increase in energy expenditure is needed. However, if the children all stand close to the edge of the roundabout, total rotational inertia increases hugely and the person driving the roundabout has to expend huge amounts of energy getting the roundabout spinning and then keeping it going.
Whilst the new compressor wheel has no more mass than the original, its increased size means more of its mass is further from the axis of rotation. As such, rotational inertia is slightly increased and more exhaust gas must pass through the turbine in order to get the compressor wheel spinning. However, once it is spinning, much more boost is created.

The Bearings

There are two bearings that support the entire rotating assembly at the heart of the turbo, namely the journal bearing and the thrust bearing. Fig. 4.6 below shows a section of Fig. 4.1, but additionally shows the location of the two bearings.

Fig. 4.6
4.6 - Turbo Bearings.jpg

The journal bearing is a supportive sleeve that wraps around the rotating shaft that links the turbine to the compressor wheel. Engine oil straight from the oil cooler is continuously poured into the journal bearing, keeping the bearing cool and well lubricated.
In Fig. 4.6, the red arrows, representing exhaust gas flow, and the smaller of the blue arrows, representing atmospheric air entering the compressor wheel, all point in the same direction. As a result, the entire rotating assembly experiences a force along its axis of rotation; as seen in the graphic above, it is continuously being pushed to the left. The thrust bearing supports the back of the compressor wheel and counteracts that axial force. Like the journal bearing, the surface of the thrust bearing is continuously covered in oil, lubricating and cooling the bearing faces.

Fig. 4.7 shows the standard journal bearing and thrust bearing. On the left, they are arranged as per Fig. 4.6. The journal bearing contains a series of holes, allowing oil to flow through the bearing. On the right, the thrust bearing is shown placed against the back of the standard compressor wheel.

Fig. 4.7
4.7 - Standard Bearings.jpg

Both of these bearings have been upgraded. An uprated journal bearing allows for better lubrication and decreased friction between the inner surface of the bearing and the shaft it supports. Less friction means the turbine and compressor wheel assembly spins with greater ease, reducing turbo lag. The original thrust bearing only supports 270° of the rear face of the compressor wheel, as can be seen on the right of Fig. 4.7. This allows for easy assembly but will not adequately support a larger compressor wheel that is capable of higher boost pressures. Consequently, this has been changed for a larger thrust bearing that supports all 360° of the rear face of the compressor wheel. This means that the larger compressor wheel is uniformly lubricated and that the axial load is evenly distributed.

The Total Product

Once fitted to the car, the final turbo appears to be absolutely standard. Whilst it’s filled with exotic components, its exterior dimensions and fitment are no different. All other parts that attach to the turbo, from oil feed pipes to pneumatic lines controlling the wastegate, do so in their usual way.
Of the internal modifications made, some increase performance but inevitably cause more turbo lag. Other modifications have been made specifically in an effort to reduce turbo lag. The combined effect of all these modifications should be a turbo that exhibits similar lag to that of the AMF enigine’s standard turbo but is capable of delivering much more boost.

Fig. 4.8
4.8 - Total Product.jpg

Under most circumstances, the compression of a gas results in the temperature of the gas increasing. Many will have noticed that, when pumping up a bicycle tyre, the pump gets hot. This is due to the temperature of the air inside the pump increasing as it is squeezed into the tyre. The same is true for a turbo; the compressed air that the turbo generates is very hot. Before this compressed air is used to burn fuel in the engine, it must be cooled down. This is the job of the intercooler.
 
Last edited:

timmus

A2OC Donor
5. The Intercooler: Compromises in Existing Choices

An intercooler is just like a radiator, designed to transfer heat from that which flows through it to the atmosphere around it. The A2’s intercooler is an air-to-air radiator; the compressed air from the turbo flows through the intercooler, giving up its heat to the atmospheric air around it. Colder air is denser than hot air, meaning it contains more oxygen for a given volume. As such, cooling the air that’s used to burn fuel promotes more thorough combustion, increasing power and efficiency. Fig. 5.1 illustrates the workings of the intercooler.

Fig. 5.1
5.1 - How Intercooler Works.jpg

The A2’s intercooler consists of three primary pieces: two ends tanks and a core. It is mounted at the very front of the car, just behind the bumper. Compressed air from the turbo (marked ‘hot boost’) enters the lower end tank and then starts to travel through the core along a series of parallel tubes. The gaps between these parallel tubes are crisscrossed with cooling fins. As the car drives along, comparatively cold atmospheric air, marked A, is funnelled through this mesh of fins, cooling down the tubes and the boost that travels within. The boost that emerges from the upper end tank is now cool, having given up its heat to the atmospheric air exiting the back of the core.

The major problem with the A2’s standard intercooler is poor build quality. The intercooler has to be able to withstand the internal pressure of carrying compressed air, but unfortunately the standard design simply isn’t strong enough to last, especially once a vehicle is remapped. Whilst the TDI75 is widely regarded as the most reliable of all the engines available in the A2, intercooler failure is nevertheless a relatively common topic. If your intercooler hasn’t yet failed, you can be sure that in time it will. The major weakness is the point where the core attaches to the end tanks, as shown in Fig. 5.2. The metal core is crimped around the plastic end tanks with a rubber seal in between. In time, this join weakens and the end tank begins to separate from the core. This causes the compressed air inside the intercooler to escape, wasting the effort of the turbo and causing the car to enter ‘limp home mode’.

Fig. 5.2
5.2 - Intercooler Failure.jpg
(Photo credit: Vincenzo Saiya, Stealth Racing UK Limited)

Should an A2 be afflicted by this problem, all existing solutions have intrinsic compromises. A like-for-like replacement from Audi is expensive and will, in time, fail in the same way. Various third-party manufacturers make much cheaper copies, but they usually suffer the same fate only sooner.
In early 2008, Forge Motorsport attempted to solve this problem by manufacturing an intercooler entirely from alloy, devoid of any problematic seals between different materials. The Forge intercooler was first commissioned by Stealth Racing for an A2OC member whose existing intercooler had failed. Their car was off the road until a replacement could be manufactured, meaning the development process was rushed. Whilst the Forge intercooler solved the problem of the failing seal, it introduced a series of other shortcomings, all caused by one fundamental design flaw, namely its size.

The Forge intercooler is big. Whilst its frontal area is no greater than that of the standard Audi intercooler, it is twice as deep and therefore has twice the internal volume. Whilst conventional wisdom would suggest this will result in better cooling due to the boost spending twice as long in the intercooler, the unusual positioning of the A2’s intercooler means it’s likely the opposite is true. The A2’s intercooler sits behind the front bumper, where there is very little flow of atmospheric air needed to cool the core. The only part of the intercooler that is directly exposed to airflow is the lower third, which sits just behind the lower grille between the fog lights. In order to ensure that atmospheric air passes through the entirety of the intercooler, Audi have designed a scoop that draws air upwards from the lower grille and downwards from just beneath the service flap, forcing it through the more sheltered sections of the intercooler. The Forge unit is so thick that its leading face is pushed into the void behind the front bumper, meaning it is only more sheltered and there is no longer space for the scoop to be fitted. As such, the upper two thirds of the Forge unit are completely sheltered behind the front bumper, resulting in only the lower third performing its job as a heat exchanger.
A sheltered intercooler also increases the likelihood of heat soak. Heat soak occurs when the intercooler can't dissipate the heat that it absorbs from the boost air fast enough, causing the intercooler temperature to gradually rise. When the intercooler can no longer extract any more heat from the boost air, its effectiveness is lost.
The problems due to its size don’t end there. When the turbo first spins up, it has to compress a slug of air between its compressor wheel and the engine's air intake. Before that slug of air is compressed, the engine feels no benefit from the turbo. The total volume of the intercooler is therefore one of the many things that contributes to turbo lag. As mentioned, the Forge intercooler has an internal volume approximately twice that of the OEM intercooler, meaning the turbo has a lot more work to do before its effects are felt. The additional depth of the core also means that the intercooler presents greater resistance to the air trying to flow through it, meaning more air is likely to spill around the sides of the unit rather than travel through the heat exchanger. Furthermore, Forge’s unit is extremely heavy. The A2 TDI is already very nose-heavy, so mounting additional weight at the very front of the car, forwards of the front wheels, is to be avoided.
Whilst the Forge intercooler solves the problem of reliability, it cannot be considered a performance product and the consequences of its design are in conflict with my OEM philosophy. Another solution to the intercooler problem is needed.
 
Last edited:

timmus

A2OC Donor
6. The Intercooler: A No-Compromise Solution

The ideal intercooler for the A2 TDI needs to fit the car as Audi intended, retaining the air scoop that’s fitted to its leading face. It also needs to have bulletproof reliability, without the fragile joins between the core and the end tanks. In order not to increase turbo lag, its internal volume must be no greater than the original Audi unit. It must also be a highly effective heat exchanger, able to remove as much heat from the boost air as possible without resulting in heat soak. Fig. 6.1 below shows a new intercooler design that achieves exactly this, while Fig. 6.2 shows the original Audi unit for comparison. As can be seen, all exterior dimensions and mounting points are identical. As such, the new intercooler fits the A2 as Audi intended, without the need to modify any components of the car in any way.

Fig. 6.1
6.1 - Timmus Intercooler.jpg

Fig. 6.2
6.2 - Audi Intercooler.jpg

Fig. 6.3 shows the intercooler mounted on the car with the air scoop fitted in front. As the car drives along, cool atmospheric air, marked A, travels over and under the front bumper, represented by the obstruction marked FB. With the scoop fitted, this air is funnelled through the intercooler, thus negating the shelter of the front bumper.

Fig. 6.3
6.3 - Air Flow.jpg

A frontal view of this arrangement, as shown in Fig. 6.4, further emphasises the indispensability of the scoop. The blue rectangles highlight the areas over which the scoop collects atmospheric air, whilst the red rectangle highlights the total frontal area of the intercooler’s core, through which atmospheric air must flow. The total blue area is 6% larger than the red area, meaning plenty of atmospheric air is collected to cool the entirety of the core. Were the scoop not fitted, the area shaded in purple is the only section of the intercooler’s core that would experience the flow of atmospheric air. It is just 37% of the total core. This demonstrates that OEM fitment is vital.

Fig. 6.4
6.4 - Areas.jpg

The scoop results in a lot of atmospheric air approaching the intercooler’s core at an angle, as indicated by the blue arrows, marked A, in Fig. 6.3. On the standard intercooler, the cooling fins that crisscross the gaps between the parallel tubes are continuous from front to back, meaning only air that approaches the intercooler head-on passes through the core easily. Fig. 6.5 shows how these fins have been redesigned to allow air to pass through the core at a much greater range of angles.

Fig. 6.5
6.5 - Fins.jpg

Rather than the fins running as continuous sheets from front to back, they are instead made up of a series of very thin fins that have been offset relative to one another. As such, air approaching the core at an angle also finds an easy path through, increasing flow and thus aiding cooling.

The parallel tubes have also been improved. Fig. 6.6 shows a cross-section of the parallel tubes as seen from inside one of the end tanks. A series of internal fins increases the inner surface area of the parallel tubes enormously. As a result, the hot boost entering the parallel tubes loses its heat to its surrounding structure much more readily, resulting in more efficient cooling without increasing intercooler volume.

Fig. 6.6
6.6 - Tubes.jpg

Lastly, the intercooler is powder coated in black. Although it is made entirely of alloy and therefore not susceptible to corrosion, the coating further protects the intercooler against debris and weathering. Being black also increases its ability to absorb and dissipate heat, further adding to its effectiveness.

Fig. 6.7
6.7 - Powder Coating.jpg

The boost air that exits the intercooler is now in an ideal state for burning fuel; cold, dense and full of oxygen. However, before it’s used, it must travel from the front of the car to the rear of the engine, passing through a hot engine bay. Keeping it cold in this environment is the next challenge.
 
Last edited:

timmus

A2OC Donor
7. The Inlet Manifold

The inlet manifold splits the flow of cold boost arriving from the intercooler between the engine’s three cylinders. It isn’t a particularly complex piece, though it is meticulously designed to ensure smooth and even distribution of the incoming boost. Fig. 7.1 shows the standard inlet manifold. Cold boost arrives from the intercooler at P and is divided between the runners, marked R1, R2 and R3. Each of the runners then feeds air into its associated cylinder, marked C1, C2 and C3.

Fig. 7.1
7.1 - How Manifold Works.jpg

The same manifold is used on other VAG cars that are fitted with the 1.4 TDI. Various other components sometimes need to be bolted to the inlet manifold, so the manifold is manufactured with a few attachment points, as highlighted in Fig. 7.1. In the A2, these attachment points serve no purpose. A bitumen-like covering is also applied to an area of the manifold, presumably as a method of noise reduction or as a partial thermal barrier.

The runners of the inlet manifold sit nestled among the exhaust manifold (reference Fig. 4.2), which is extremely hot. As such, thermally insulating the inlet manifold against the heat of the exhaust manifold is critical if the boost air is to be kept cool. Fig. 7.2 shows how the standard inlet manifold was improved.

Fig. 7.2
7.2 - Progression.jpg

The standard manifold, shown on the left, was dipped in solvent to remove all inner and outer grime, as well as the bitumen covering. All excess metal, including the redundant mounting points and the surplus between runners 2 and 3, has been removed. A white ceramic coating was then applied to the inlet manifold, as shown on the right, in order to prevent heat transfer from the exhaust manifold.
This ceramic coating was first developed to protect components near to the reactors of nuclear power stations. It is only 0.3mm thick but is a highly effective barrier to both radiated and conducted heat, meaning the inlet manifold is much less affected by its hot surroundings and its close proximity to the searing temperatures of the exhaust manifold. Consequently, the cold boost that travels within is kept as cold as possible until the moment it enters the engine’s cylinders. Fig. 7.3 shows a close-up of the ceramic coating.

Fig. 7.3
7.3 - Runners.jpg

Fig. 7.4 shows the ceramic-coated inlet manifold from both sides.

Fig. 7.4
7.4 - Front and Back.jpg
 
Last edited:

timmus

A2OC Donor
8. Cool Connections

Although the turbo and the inlet manifold sit within close proximity of each other, the location of the intercooler at the front of the vehicle means that the boost air generated by the turbo has to travel a considerable distance before eventually reaching the inlet manifold. Keeping the boost air insulated from the heat of the engine bay is therefore important.

Between the turbo and the intercooler, there are two rubber hoses and a rigid pipe. Similarly, between the intercooler and the inlet manifold, there are also two rubber hoses and a rigid pipe.
On both AMF and BHC variants of the TDI75, the rigid pipe between the turbo and the intercooler is made of plastic. However, to withstand higher boost pressures, the same pipe on the TDI90 is made of metal. This is shown in Fig. 8.1.

Fig. 8.1
8.1 - Lower Boost Pipe.jpg

By using the metal pipe from the TDI90, a ceramic coating can be applied, thus preventing the boost air within from absorbing any heat. Whilst a white or silver ceramic coating is best at repelling radiated heat, colour isn’t a consideration when insulating against conducted heat. The location of this pipe means that conducted heat is of much greater concern, so any colour of ceramic coating will do an equally good job of preventing heat transfer. I chose green, as can be seen in Fig. 8.2.

Fig. 8.2
8.2 - Ceramic.jpg

On left-hand-drive A2s, the path from the intercooler to the inlet manifold is relatively short, but on right-hand-drive A2s, the positioning of various other components means that the cold boost exiting the intercooler must instead travel a longer, circuitous route. Consequently, thermal insulation of this section is especially desirable. On all variants of the 1.4 TDI, the rigid pipe in this section is made of metal, meaning it too will accept a ceramic coating. Fig. 8.3 shows this pipe coated in green ceramic, alongside the pipe shown in Fig. 8.2.

Fig. 8.3
8.3 - Boost Pipes.jpg

As mentioned previously, there are normally rubber hoses that connect to the ends of these pipes. Whilst the hoses perform their job acceptably well, they exhibit a number of shortcomings due to material from which they’re made. Firstly, they conduct heat, which is undesirable in this application. They also become fragile with age, resulting in splits that lead to boost leakage and ‘limp home mode’, just like a split intercooler (see Fig. 5.2). Additionally, they are prone to swelling if exposed to oil for long periods, causing weakness and eventual failure. Manufacturing these hoses from silicone instead address all these disadvantages. Silicone is an exceptionally poor conductor of heat, helping to keep the boost air cool. It’s also an incredibly stable compound, so is extremely resistant to aging and degradation, meaning greater long-term reliability. Fig. 8.4 shows a full set of four silicone hoses for carrying the boost from the turbo via the intercooler to the inlet manifold. They are, in size and shape, exactly like the OEM rubber hoses.

Fig. 8.4
8.4 - Silicone Hoses.jpg

To prevent ‘ballooning’ under pressure, the silicone hoses are reinforced with a double layer of fabric, as shown in Fig. 8.5. The fabric is highly resistant to stretching, meaning that the air pressure generated by the turbo is maintained rather than being partially wasted by the expansion of tubing.

Fig. 8.5
8.5 - Reinforcement.jpg

Combining the ceramic-coated pipes with the silicone hoses creates a complete heat-resistant pathway for the boost air, as can be seen in Fig. 8.6. The result is that little or no additional heat is absorbed between the turbo and the intercooler, and the cooling provided by the intercooler isn’t wasted as the boost air travels to the inlet manifold.

Fig. 8.6
8.6 - Cool Connections.jpg
 
Last edited:

timmus

A2OC Donor
9. Getting in the Way: The Anti-Shudder Valve and EGR Valve

In an ideal world, the boost air would be allowed to flow completely unimpeded from the intercooler, along the silicone and ceramic piping, into the inlet manifold. However, just prior to the inlet manifold, in the path of the boost, sit two additional devices, namely the anti-shudder valve and the EGR valve. Both these devices present an obstruction to flow. The AMF engine combines these two devices into one component, as shown in Fig. 9.1. The blue arrows represent the flow of boost air.

Fig. 9.1
9.1 - ASV & EGR.jpg

The anti-shudder valve is only used to stop the engine. It’s possible to stop a TDI engine from running simply by cutting its supply of diesel. However, this causes the engine to shudder to a stop rather than stopping smoothly. The solution to this problem is to also starve the engine of oxygen as well as fuel. This is achieved by introducing a butterfly valve into the flow of boost air, as shown in Fig. 9.2. When the engine is running, the butterfly valve angles itself so as to present as little obstruction to the flow of boost air as possible, shown on the left. When stopping the engine, a vacuum actuator pulls a lever on the right of the anti-shudder valve upwards, as shown on the right. This causes the butterfly valve to rotate, thus completely blocking the flow of boost air and bringing the engine to a halt.

Fig. 9.2
9.2 - How ASV Works.jpg

Directly behind the anti-shudder valve is the EGR valve. EGR is an abbreviation of exhaust gas recirculation. EGR involves taking a portion of the exhaust gas, mixing it with the boost air, and sending it through the cylinders for a second time. It is a method of reducing the amount of polluting nitrogen oxides emitted by the engine. Fig. 9.3 shows how the EGR valve works. A small branch of the exhaust system is fed to the EGR input, directly beneath the EGR valve. When vacuum is applied to the EGR actuator, the EGR valve lifts upwards, like the lid being removed from a cauldron, causing exhaust gas to mix with the boost air.

Fig. 9.3
9.3 - How EGR Works.jpg

Whilst the objective of EGR is unquestionably commendable, it has a number of undesirable consequences. Firstly, it causes the boost air to get hot. Having invested so much in getting the boost air as cold and as dense as possible, it is totally counterproductive to mix it with hot, oxygen-depleted exhaust gas just prior to entering the cylinders. This dilution of the boost air, accompanied by the obstruction to flow presented by the EGR valve, causes decreased performance and increased fuel consumption. EGR also causes a gradual build-up of sticky tar in the inlet manifold, cylinder head valves and the EGR valve itself, as shown in Fig. 9.4. This introduction of abrasive contaminants leads to increased component wear and increased engine oil acidity, both of which reduce the longevity of the engine. EGR also increases soot and particulate matter emission, meaning that its positive environmental consequences are counterbalanced by a negative environmental consequence.

Fig. 9.4
9.4 - Sticky Tar.jpg

I intend to keep my A2 forever. Whilst I believe that EGR has a net positive environmental impact for those with a disposable attitude towards their cars, the same cannot be said when a vehicle is destined to be eternally cherished and maintained. As such, I have decided to completely eliminate the EGR system. It is my choice based on the pros and cons. Others are, of course, welcome to disagree with me, but I’d rather discussion/argument about this topic be conducted elsewhere.

The AMF engine combines the anti-shudder valve and EGR valve into one component, which means that removing the EGR without also removing the anti-shudder valve is a challenge. Whilst the BHC and ATL engines split these devices into two separate components, making the removal of just one very easy, the standalone anti-shudder valve is unreliable. Graham – forum stalwart Spike – devised a clever solution to this problem, allowing the EGR valve to be removed from the combined unit, leaving the more reliable anti-shudder valve intact. Fig. 9.5 shows that the EGR input has been capped with a blanking plate. The additional black component attached to the anti-shudder lever is the vacuum actuator, as mentioned in reference to Fig. 9.2.

Fig. 9.5
9.5 - Input Blanking Plate.jpg

However, there’s more to this blanking plate than first meets the eye. Graham has painstakingly removed all the internal components related to the EGR valve, meaning they no longer present an obstruction to air flow. Fig. 9.6 shows that the blanking plate has been precisely machined to fill the hole left behind by the blanking of the EGR input and the removal of the EGR valve. The result is that the internal wall is completely smooth, aiding air flow, and no evidence of the EGR valve remains.

Fig. 9.6
9.6 - Machined.jpg

Fig. 9.7 shows a comparison of the old unit compared to the new unit made by Graham. Only the anti-shudder valve remains, presenting much less obstruction to the flow of boost air.

Fig. 9.7
9.7 - Old vs New.jpg

Graham, I shall remain eternally grateful to you for making this unit for me. It has allowed me to eliminate the EGR system without compromise. I’m delighted to have a piece of your engineering as part of my project. Fig. 9.8 further demonstrates what a gifted and inimitable gent Graham is and what an asset he and his knowledge are to A2OC.

Fig. 9.8
9.8 - ASV EGR Sides.jpg
 
Last edited:

timmus

A2OC Donor
10. High Flow Fuel Injectors

Having successfully delivered lots of oxygen-rich air to the cylinders, fuel must now also be delivered. The TDI engines in the A2 deliver fuel using PD injectors. PD is an abbreviation of the Germany term ‘pumpe düse’, meaning pump jet in English. Fig. 10.1 shows a PD injector. There is one injector for each cylinder, so three are required to run the A2 TDI.

Fig. 10.1
10.1 - PD Injector.jpg

As the camshaft rotates, the spring at the top of the injector is squeezed, causing the fuel inside the injector to be compressed. The fuel is compressed to immense pressures of approximately 1900 bar, which is roughly 800 times the air pressure generated by the turbo. At just the right moment, the engine management unit instructs the injector to fire by sending a signal into the injector’s electrical connector, shown on the right. Upon receiving this signal, the tip at the very bottom of the injector opens, causing the fuel to escape into the cylinder as a fine spray. Here, the fuel mixes with the compressed air supplied by the turbo, causing the fuel to combust. This combustion releases energy that ultimately powers the car.

In order to release more energy, thereby creating a more powerful engine, more fuel is needed. To achieve this, injectors are needed that are capable of spraying more fuel into the cylinder with each instruction from the engine management unit. The more fuel an injector is capable of spraying, the higher its flow rating. The flow rating is expressed as the output power of an engine when using four identical injectors. A standard 1.4 TDI uses PD100 injectors, meaning the injectors are capable of delivering enough fuel to generate approximately 100bhp when working as a group of four. However, the 1.4 TDI is a 3-cylinder engine, meaning only three injectors are used. Three quarters of 100 is 75, hence why the standard 1.4 TDI is referred to as a TDI75.

The standard injectors are capable of delivering a bit more fuel than their flow rating would suggest. This excess capability is what makes regular remapping possible. By asking the turbo and the fuel injectors to work at their absolute upper limit, it’s possible to generate more than the rated 75bhp without making any physical alterations. However, in order to generate 120bhp, fitting injectors with a higher flow rate is essential. Fortunately, these are commonplace in other VAG diesel engines, so are readily available. I have chosen to fit PD150 injectors, as shown in Fig. 10.2. They are exceptionally sensitive to contaminants, hence why they are photographed in their protective bags.

Fig. 10.2
10.2 - PD150.jpg

Warning: do not install high flow fuel injectors without also increasing the turbo’s ability to supply oxygen. A custom remap performed on a rolling road is essential in order to avoid over fuelling and bore wash.
 
Last edited:

timmus

A2OC Donor
11. All United

All the components listed so far can be seen loosely assembled in Fig. 11.1. It shows how all the upgraded parts attach to each other and to the core engine.

Fig. 11.1
11.1 - All United Sides.jpg

Exhaust gas travels along the exhaust manifold (1) and then spins the turbine (2) as it escapes into the exhaust pipe. The spinning of the turbine causes the compressor wheel (3) to spin, thus generating compressed air called boost. This boost is hot, so must travel along piping (4) in order to be cooled by the intercooler (5). Once cool, the boost travels along more piping (6), through the anti-shudder valve (7) to the inlet manifold (8). The inlet manifold divides the boost between the three cylinders, where is it used to burn fuel supplied by the injectors. Once combustion of the fuel is complete, the boost has become exhaust gas. It exits the engine via the exhaust manifold, causing the turbine to spin. As the turbine spins, so does the compressor wheel, thus creating more boost and keeping the cycle going.

When fitted to the car, the intercooler is mounted vertically, meaning the core engine leans back much further than Fig. 11.1 would suggest. The engine remains far from functional, hence why black tape has been applied to cover fluid holes that must remain free of dust and debris. Although just loosely held together with a few nuts and bolts in select places, this minimal assembly clearly demonstrates how a TDI engine supplies itself with oxygen. This same assembly can be seen in Fig. 11.2 through to 11.8.

Fig. 11.2
11.2 - Back.jpg
The EGR output on the exhaust manifold has been capped with a genuine Audi blanking plate. The EGR input on the underside of the anti-shudder valve has also been capped, thus eliminating the EGR system entirely.

Fig. 11.3
11.3 - Compressor.jpg

Fig. 11.4
11.4 - All United Manifolds.jpg
The runners of the inlet manifold sit extremely close to the intense heat of the exhaust manifold, hence why a ceramic coating that rejects both radiated and conducted heat is advantageous.

Fig. 11.5
11.5 - Angle.jpg

Fig. 11.6
11.6 - Back Section.jpg

Fig. 11.7
11.7 - All United IC Turbine.jpg

Fig.11.8
11.8 - Angle Section.jpg

In order to run, the engine needs much more than just air and fuel. It will need to be able to keep itself cool and supply lubrication where needed. It will need to generate electricity in order to run its engine management system and power the fuel injectors. It will need to filter the incoming atmospheric air and clean its oil, and much more besides. Many of the parts needed to perform these functions had to be taken from my A2’s original engine, so before any further progress could be made, the existing engine had to be removed.
 
Last edited:

timmus

A2OC Donor
12. Out with the Old

I gave my A2 a wash in the sunshine and then reversed it onto the lift. I switched off its engine for the last time with 191,000 miles on the clock and thanked it for its reliable service. Bit by bit, the car’s front end was dismantled until the engine was accessible. Fig. 12.1 shows my A2 ready to have its engine removed. The engine hoist stands to the left, ready to free the engine from its home of 15 years.

Fig. 12.1
12.1 - Front End Off.jpg

Once the engine was removed, it was mounted on the engine stand, ready to yield components for the new engine. This can be seen in Fig. 12.2. The oil filter housing, toothed wheels for the camshaft and crankshaft, various brackets and bolts, heat shields, etc were all removed for use on the new engine. None of these components wear out, so there was no reason not to recycle.

Fig. 12.2
12.2 - Old Engine.jpg

This was one of the last jobs to be done at WOM Automotive before they moved to their new premises. Their previous workshop was quite small, meaning space was limited when a car was on the lift. As such, my car was pushed outside whilst the new engine was built, as can be seen in Fig. 12.3.

Fig. 12.3
12.3 - Outside.jpg
 
Last edited:

timmus

A2OC Donor
13. Piecing Things Together

With all the required parts, the process of building the new engine could begin in earnest. The new core engine was mounted on the engine stand and all necessary workshop manuals were opened on the laptop. Every procedure was followed to the letter and every nut and bolt was tightened to the required torque. Every component that was removed from the old engine was meticulously cleaned and refurbished where required. New seals and gaskets were used throughout. I may even have been caught polishing bolt heads!

Fig. 13.1 shows the first stages of the build. The timing belt is fitted, employing the later design of tensioner. The camshaft position sensor can be seen fitted at the 5-o’clock position of the toothed camshaft wheel. The oil level sensor is fitted in the top of the sump, to the left of the toothed crankshaft wheel. The large bracket that holds the alternator and air conditioning compressor is bolted to the front face of the engine, on the right.

Fig. 13.1
13.1 - Timing Belt.jpg

Fig. 13.2 shows the turbo fitted to the cylinder head. The EGR output blanking plate has been fitted to the exhaust manifold. A new oil feed pipe will pour oil into the turbo, keeping the bearings cool and lubricated, and a new oil drain returns the oil to the sump, via the cylinder block.

Fig. 13.2
13.2 - Turbo.jpg

Fig. 13.3 shows the back of the engine. The upper engine mount has been fitted over the timing belt. The fuel pump and vacuum pump have been installed on the left-hand end of the camshaft. Coolant distribution pipes have been fitted to the left-hand of the cylinder head, along with the green coolant temperature sensor. The black rocker cover at the very top of the engine has been removed, allowing the camshaft and rockers to be seen. The rocker bolts have been loosened, ready for the fuel injectors to be fitted. Of all the photos I took throughout this project, this is one of my favourites.

Fig. 13.3
13.3 - Cover Off.jpg

Fig. 13.4 shows the rockers removed and the fuel injectors installed.

Fig. 13.4
13.4 - Injectors.jpg

Fig. 13.5 shows the rockers reinstalled. As the camshaft rotates, the rockers compress each injector in turn. The middle injector is shown undergoing compression.

Fig. 13.5
13.5 - Rockers.jpg

Fig. 13.6 shows the black rocker cover refitted at the top of the engine. The ceramic-coated inlet manifold has been bolted to the back of the cylinder head. The timing belt covers have been installed and the auxiliary belt pulley has been installed on the end of the crankshaft. The auxiliary belt drives a new alternator as well as the original air conditioning compressor. The auxiliary belt and tensioner are both new.

Fig. 13.6
13.6 - Auxiliary.jpg

The engine must now be removed from its stand in order for further progress to be made. Fig. 13.7 shows the flywheel installed on the opposite end of the crankshaft. The oil filter housing and oil cooler are fitted to the front of the engine, shown here on the left.

Fig. 13.7
13.7 - Flywheel.jpg

Fig. 13.8 shows the engine almost fully assembled, with its clutch installed against the flywheel and the pressure plate fitted over the top. The engine is now ready to be mated to the gearbox. Only once the engine is in the car can its remaining components be fitted.

Fig. 13.8
13.8 - Clutch.jpg
 
Last edited:

timmus

A2OC Donor
14. In with the New

With the new engine ready, it was mated to the ultimate 6-speed gearbox, which had been freshly cleaned with a toothbrush and filled with new gearbox oil. The gearbox shift tower bearings were also renewed and the selector mechanism cleaned and lubricated. The engine and gearbox can be seen in Fig. 14.1, supported by the engine hoist, all set for installation.

Fig. 14.1
14.1 - Gearbox.jpg

With the workshop clear, my A2 was pushed back onto the lift. Fig. 14.2 shows my A2 waiting to have its new engine installed. However, it’s not often that the engine bay is so easily accessible, so various other jobs were carried out before the engine was fitted. The original anti-roll bar was removed and replaced with the H&R anti-roll bar, along with Meyle HD drop links. Everything forwards of the windscreen was meticulously inspected, cleaned and restored where required. The windscreen wiper motor was dismantled and rebuilt, the wiring looms had new tape applied, the air conditioning seals were renewed, etc, etc. I even hoovered the black fabric on the bulkhead. Given the ease of access, the looms required to retrofit heated washer jets and washer fluid level monitoring were added.

Fig. 14.2
14.2 - Ready.jpg

Fig. 14.3 shows the engine and gearbox fitted in the car. At first, the old starter motor and fuel pump were fitted, as these components would experience a reasonable degree of stress in getting the engine running for the first time. Once the engine was primed and could repeatedly start ‘on the button’, both the starter motor and fuel pump were exchanged for new parts.

Fig. 14.3
14.3 - Engine In.jpg

Now it was time to reassemble the front panel and fit it to the car. As with the engine bay, every piece of the front panel was examined, cleaned and refurbished as necessary. The results can be seen in Fig. 14.4. Notice the all-alloy intercooler mounted on the right hand side.

Fig. 14.4
14.4 - Front Panel.jpg

Fig. 14.5 shows the front panel fitted to the car. The intercooler scoop, as previously shown in Fig. 6.3, can be seen installed to the left of centre.

Fig. 14.5
14.5 - Radiators.jpg

With the front panel fitted, the engine was filled with fresh oil and coolant and was then able to be started for the first time. The engine was allowed to run until it reached optimum temperature, at which point it was switched off and had its oil drained. Consequently, any residual particles from manufacturing processes were flushed out. The engine was once again filled with fresh oil, but was this time allowed to drive out of the workshop. Fig. 14.6 shows my A2 reborn, albeit with some reassembly still required.

Fig. 14.6
14.6 - Reborn.jpg

After some testing, Fig. 14.7 shows the car waiting to get back into the workshop for its reassembly to be completed.

Fig. 14.7
14.7 - Awaiting Completion.jpg

Fig. 14.8 shows the new engine neatly sat in its home. It is mostly an AMF engine but employs crucial parts from the BHC and ATL (TDI90) engines.

Fig. 14.8
14.8 - Home.jpg
 
Last edited:

timmus

A2OC Donor
15. Simplified Vacuum System

On A2s fitted with the AMF engine, there are usually three valves mounted to a bracket at the back of the engine bay, behind the coolant expansion tank. The opening and closing of these valves is controlled electrically by the engine management unit. When instructed to do so, they distribute either pneumatic pressure or vacuum to the turbo’s wastegate actuator, the anti-shudder actuator or the EGR actuator. Due to the EGR system having been removed entirely, the valve that controls the EGR actuator, known as the N18 valve and shown in Fig. 15.1, can also be removed.

Fig. 15.1
15.1 - EGR Control.jpg

The removal of this valve and all its associated tubing significantly reduces the common untidiness at the back of the engine bay. Fig. 15.2 shows the remaining two valves. The black valve on the left controls the anti-shudder system and the pale brown valve on the right controls the turbo’s wastegate. It is via this brown valve, referred to as the N75 valve, that the engine management unit is able to regulate the amount of boost that is generated by the turbo.

Fig. 15.2
15.2 - Valves.jpg

The removal of the N18 valve also means that the long, unsightly tube that emanates from the atmospheric air pipe just prior to the MAF sensor can be removed. Fig. 15.3 shows the remaining attachment point for this tube, with a small blanking cap applied. This attachment point now serves as a useful anchor for the windscreen scuttle drainpipe.

Fig. 15.3
15.3 - Reference.jpg

The final outcome is a very neat pneumatic and vacuum system, with a minimal amount of tubing that all runs in one loom along the very back of the engine bay, as can be seen in Fig. 15.4.

Fig. 15.4
15.4 - Lines.jpg
 
Last edited:

timmus

A2OC Donor
16. Remap and Results

A car's map is basically a software look-up table that allows the engine management unit to calculate how much fuel and air to supply based on the readings from all the electronic sensors as well as the accelerator position. The map stored on my engine management unit was written by Audi for a TDI75 with a standard turbo, PD100 injectors and an EGR system. My engine no longer matches that description, so a new map must be written that is tailored for my unique engine. After completing its reassembly, my A2 was loaded onto the back of a trailer and towed to a rolling road. Driving the car on the rolling road, as shown in Fig 16.1 and 16.2, allows a bespoke map to be written and the engine’s power output to be calculated.

16.1
16.1 - Rolling Road 1.jpg

16.2
16.2 - Rolling Road 2.jpg

I plan on having the engine remapped by various establishments to see who can write the best map. The company whose rolling road is pictured above are experienced at writing maps for TDIs fitted with high flow fuel injectors, hence why they were chosen to write the first map. However, given that Stealth Racing have remapped more A2s than anyone else and had remapped my previous engine, I shall post comparative performance graphs once my new engine has paid them a visit. All rolling roads are calibrated slightly differently, so I think this will allow for the most meaningful direct comparisons. However, at the moment, my engine is producing exactly 120bhp. In terms of torque, it is producing 250Nm, which is the rated upper limit of the gearbox.

Since it was remapped, I’ve driven nearly 10,000 miles, so have got to know the new engine well. It’s utterly wonderful. My A2 is undoubtedly a faster car than it was before, but my greatest pleasure comes from how smooth, quiet and refined it is compared to the standard 1.4 TDI. It revs freely across the entire rev range, always seeming totally comfortable and never sounding stressed or throaty. Numerous club members have been a passenger in my car since the new engine was fitted and have all commented on what an exceptionally quiet engine it has.

Although it produces fractionally more power than a remapped TDI90, they remain very different engines and I’d wager that my car isn’t as quick to accelerate from standstill. The TDI90’s variable vane turbo delivers peak power and torque much lower down the rev range than my A2’s wastegate turbo, which exhibits the same turbo lag as any other TDI75. In many ways, my A2 still drives like a TDI75; it just happens to be a very fast TDI75 capable of silky, effortless acceleration.
 
Last edited:

timmus

A2OC Donor
17. Conclusions

I set out to create my ultimate 1.4 TDI; an engine with the simplicity, efficiency and reliability of the TDI75 and with the performance of a remapped TDI90. In terms of performance, peak power output has been equalled, even though the delivery of that power is different. It doesn’t urge you to go faster when you don’t want it to, allowing you to pootle about without feeling hassled by your own car. However, when you want it to go, it’ll go, creating an addictive turbo whistle to accompany the acceleration. It definitely has the split personality I was hoping to achieve. So far, I’ve only noticed a reduction in fuel efficiency when it’s being driven in a spirited manner, which is to be expected. It remains every bit the frugal, long-distance mileage muncher it’s always been. In terms of reliability, only time will tell, though the omens are good. My A2 has the most reliable version of every engine component: a single-mass flywheel, a wastegate turbo, the vacuum-actuated anti-shudder valve, etc. Fingers crossed, I see no reason why it won’t deliver decades of service.

I’m very pleased that, despite all the refinements, the engine retains all that’s charming and quirky about the A2 TDI. I never feel as though I’m driving a car that’s had an engine transplant. My aim was to keep the build of the engine and its installation as per factory and I feel that’s definitely been achieved. Look under the bonnet and, notwithstanding the bright colours, everything looks normal and is in it right place. The Audi workshop manuals still apply to my car.

There is most definitely still scope for further development. As mentioned, I plan on getting the car remapped on at least one other rolling road and then selecting my favourite map. I’d like to look at improving the exhaust and, although only cosmetic, it would be nice to have a more attractive engine cover than the one fitted at factory.

Not infrequently, I drive A2s that are totally factory standard. They’re great, though always serve as a stark reminder of how much I’ve developed my own A2. With its silky engine, a 6-speed gearbox, wide-ranging suspension upgrades and my wheels and tyres of choice, my A2 hasn’t lost any of what makes it an A2. It’s the same car it’s always been, with the same character and the same appearance, but yet it’s totally different. I utterly adore it.

16.3 - Done.jpg
 
Last edited:

timmus

A2OC Donor
18. Reflections and Acknowledgements

The publishing of this article brings to a conclusion something to which I have devoted an awful lot of time and energy. Between my other professional pursuits and working on club members’ cars, I have driven thousands of miles and had countless meetings with manufacturers. I’ve stayed up late into the night researching, done trial fitments and refinements, and collectively spent months in workshops and garages. It’s been utterly fantastic and it feels a little odd to be reflecting upon it rather than still being in the thick of it. The seeds of this project were sewn nearly 5 years ago. Although I never imagined it would grow into what it has become, the idea that I would document every stage and eventually write this article was there from the beginning. I wanted to write an article that would be interesting to those with prior knowledge and accessible to those without. It has in itself been a huge undertaking. I’ve spent weeks selecting and editing photos, creating diagrams, thinking of ways to explain things, composing text and bringing structure to 12,000 words. Whether or not I’ve been successful, only you can decide.
One thing, however, is certain; a project like this cannot be done alone. Finding manufacturers willing to take on jobs and work to my pedantic standards wasn’t always easy, but those who were willing to embrace my project have all been outstanding. You know who you are. There are also a number of people from this community to whom I’d like to express my heartfelt gratitude for their contributions...

Sarge
Quite simply, I would not love my car’s new power plant half as much as I do were it not for your kindness. Had I done all these upgrades to my previous engine, there’d have still been 191,000 miles on the clock and an enduring ignorance about how previous owners may have treated it. You’ve allowed me to truly reset the mileage under the bonnet and get closer to owning a new A2 than I ever imagined possible. I remember when you first acquired the new engine, I looked upon it and wished I could also have a new engine. I never entertained the idea that it would one day be mine. I will cherish it and make sure it always receives the best possible care. Thank you so, so much.

Hilary (YorkshireHill)
Hilary, when your FSI went for a rather catastrophic unpiloted excursion, I never imagined its front panel would end up as part of my car. Much of what you see in Fig. 14.4 is from your FSI. Given its comparatively low mileage, the components you gave me from your car were generally in better condition than those I removed from mine. So, you’ve also helped me to roll back the years. Thank you very much.

Mo (Audi2012)
Mo, when I bought your crashed A2, it was my sincere hope that it could be brought back to life. Unfortunately, the damage was too extensive and so I had no choice but to break it for parts. However, its value to this project cannot be understated. Your car’s intercooler is featured in Fig. 5.1 and 6.2 and was the unit on which the new intercooler was modelled. The silicone hoses wouldn’t be the right shapes were it not for the rubber counterparts given up by your car. The engine management unit from your breaker now runs the TDI120. Additionally, I’ve used your old car for trial fitments, not just related to this project but for many retrofits. It has proven invaluable and, although it might no longer exist, it most definitely lives on. Thank you, Mo.

Bruce (Rainman)
Bruce, I know you intended to fit the dipped inlet manifold to your A2, but unfortunately circumstances transpired against you. I hope you’re happy with its new home. The ceramic coating could never have been applied were it not for your efforts in getting it back to bare metal. It’s a beautiful piece of this engine that I’m proud to own. Many thanks to you.

Jeff (Mustang Owner)
Jeff, you probably remember that, some years ago, you gave me a brand new Webasto. This exceptional generosity will keep my cherished engine comfortable throughout many British winters to come. Your contribution has also played a huge part in rolling back the years and I’m hugely grateful. Thank you.

Murdo
Murdo, you have provided neither parts nor knowhow to this project, but instead I thank you for your unfailing confidence, encouragement and support. That intermittent feeling that I may have bitten off more than I could chew was consistently but kindly stomped on by you! A thousand thank-yous.

Rob and Marcus of WOM Automotive (chumsofmanutd)
Rob, I know of no one else who provides such a flexible, tailored service. Across the board, you really do define customer-orientated service. You’ve been endlessly accommodating and I cannot thank you enough for the huge logistical part you have played in this project.
Marcus, you’ve been an ever-present source of advice and friendly discussion throughout this project, but during the build stage in particular, you were invaluable. Interested, enthusiastic and hugely knowledgeable, you embraced my philosophy and worked with a care and eye for detail like no other mechanic I’ve ever met. I could not have achieved this without you.

Graham (Spike)
Graham, your contribution to this project has been immense and your specialist knowledge of diesel engines has been a decisive factor in its success. Aside from the vast amount of time you invested in making the perfect anti-shudder valve, you’ve been a sounding board for my ideas and contributed your considerable expertise generously and with huge enthusiasm. Collaborating with you on this has been a great deal of fun. You’re as responsible as I am for the creation of the TDI120. Thank you very, very much.
 
Last edited:
Top