We have already presented our latest project—Subaru Impreza N14 VRT. A very interesting feature of this car will be the engine. This rally car will use a newer FA20DIT engine, but that’s not the only interesting thing. This engine will not be the normal 2.0 liter, but a smaller one—1.8 liter. The question is—why? So, let us dive more into the technical details and answer that question.
So this car will use the FA20DIT engine that is used in newer Subaru models, but not in the STI. This engine features direct injection, which can be found in the WRX models for the US and Japanese markets. The Subaru Forester in Europe has a very similar engine but with differences and less power.
In the technical regulations of rallying, the weight of the car and engine displacement go hand in hand. The larger the engine capacity, the higher the minimum weight of the car is required by the rules. This rule is widespread and balances out the power-to-weight ratio. This is important to maintain competition between the different cars. If the engine has a turbo, the cubic capacity is multiplied by a coefficient of 1,7. So if the total displacement is over 3,000 cc, the car should weigh at least 1,300 kg. With less than 3,000 cc, the weight can be 1230 kg. 70 kilograms is a lot, so the idea was to build an engine under 3,000 cc. The math is simple – the original FA20DIT engine with turbo comes to 3,400 cc (2,000*1.7). So if we want to stay under 3,000 cc, we need to build an engine with 1,7647 cc (3,000 / 1.7). With a 2% allowance, we need a 1,800 cc engine. Therefore we have to make FA20DIT smaller.
But that’s not all. A smaller engine runs better than a larger one because of the turbo restrictor. The hole through which the air flows to the engine always has a diameter of 34 mm – whether at 2,000 or 7,000 rpm. The thing is that the maximum air flow rate is always the same because of the restrictor. So the smaller the cylinder displacement, the less air is required at high rpm’s. A smaller 1.6-1.8 engine therefore reaches 7000-8000 rpm more easily than a 2.0 engine, which runs out of air at 5,000 rpm. It is no coincidence why R5/Rally2 or even WRC cars use 1.6 engines.
To downsize the FA20DIT engine, we need very specific and high-quality parts. We chose ZRP Parts for this, as we have already worked together on several projects. The many years of good cooperation with ZRP made the decision easy for us. For example, we have built some S54 engines with reduced displacement from 3.9 to 3.0 liters. We used S54 engines with S50 custom billet crankshafts and connecting rods from ZRP. These engines are still running perfectly and we will be competing with one at the 100 Acre Wood Rally in the USA. Our friends at MV Sport have also built a similar engine for circuit racing.
This Subaru engine project is absolutely unique and kind of crazy, so we are very grateful that ZRP took up this idea and agreed to help us make very special parts for this engine for a very special Subaru. We hope that this unprecedented project will benefit ZRP in the way of engineering ideas and bring fame among the worldwide Subaru community. The engine will be completed by Alex Drakos from ZRP and Vladas Ciunelis from Pono Vlado Motorai.