I have to second yurimacs, the turbo tech for this game is stuck in the 80’s. Single geometry, single vane turbochargers. My understanding of the physics of how turbos work means that the higher the pressure (which is represented at boost - atmosphere for the pressure ratio) the smaller the efficiency area is. A turbo boost map looks like a topographical map.
In this example we see the “boost island” ranges from 1.8 to 3.0, or about 8-14 PSIa (here we use PSIa or absolute since atmosphereic air pressure is included when calculating the weight of the air). We then compare this to the mass air flow, or the weight of the air being consumed by the engine. This chart is in KG/s, and 1 cubic meter of air weighs 1.27Kg. A liter of gas is 0.71-0.77 Kg (depending on grade), and fuel + air = power.
Now, why did I turn this into a math lesson? The boost chart here is for an 11 PSI turbo, and you see how small the island is, anything outside the middle area is less than ideal, and the line on the left/top is called the surge line. This is a bad place.
Now lets look at a case study for an non-turbo engine. Burning fuel makes heat, but only about 1/3 of that heat is converted to power. To make 300 HP in an engine you woule need to burn about 91L of fuel per hour. That’s about 68Kg of fuel in the same time. I have yet to mention stoichiometrics, this the the fuel air ratio (in the fuel tab). The ideal ratio is 14.7:1 for gasoline, or around 7% fuel by volume. This can (and should) be adjusted in certain configurations. So to burn 68Kg of fuel, you need to burn 990Kg of air, or about 780 cubic meters.
What does it all mean? If a 2L engine made 185HP then 11Lbs of boost and bigger injectors (to maintain the ratio) will make 300HP at the same RPM. Anything above 6-8 Lbs requres a special bult engine. Boost is not simple.
Obviously there are variables, and a trubo recycles a lot of the heat lost on the exhaust (also roughly 1/3), and none of this takes into acount engine displacement, RPM, or volume efficency, but you get the idea of why massive boost numbers just don’t work. Plus the inertia of a single turbo would make it borederline undriveable. In your example, that car does not have a lockup torque converter, the “staging” at the beginning of the race give the turbo the several seconds it needs to spool up, then the transmission slips to allow the engine to just stay in the very narrow pressure ratio.