The basics of supercharger calculators …
Supercharger calculators are based on several basic equations that govern performance and the physical rules that tie superchargers together. At the heart of the matter, superchargers work according to the ideal gas law, where PV = pressure NRT x volume = number of gas molecules X a constant temperature X. What superchargers do is they feed the engine with more air molecules, supercharging the engine with forced air. This air is forced into the engine due to the supercharger blowing more air into the engine inlet than the engine would normally breathe on its own device. The result of this ‘forced induction’ can be observed and measured in one of two ways: pressure or temperature. In an ideal world, with a supercharger that has perfect adiabatic efficiency, we can feed the engine with twice the number of air molecules (to double the horsepower figure), doubling the intake air pressure (at 2.0 atmospheres or so). which we call 15 pounds). per square inch (PSI) of impulse). In the real world, superchargers are not 100% efficient, so doubling the inlet boost pressure may give us less than twice the horsepower due to the following:
P * V = n * R * T Pressure increases by a factor of 2 The volume is fixed The number of gas molecules increases by 80% (or a factor of 1.8) The temperature increases by a factor of 11% (or a factor of 1.11) If we look at our equation above, we can see: 2 * P * V = 1.8 * N * R * 1.11T The equation is balanced as 2.0X1 = 1.8 * 1.11 (the pressure rise equals the combined effect of the increased air flow and increased temperature).
From here, we can also see that even at the same level of ‘boost’, a more efficient supercharger can generate more horsepower because more of the supercharger’s power is translated into compression and airflow rather than boost. thermal … Do we take these equations to the “real world” in terms of power and power? Let’s start with a 2.0 liter (volume), 140 hp (air molecules) engine. Let’s say we have a target of 280 horsepower. Our flow ratio will be related to the ratio of our target power to our current power … Density ratio = 280/140 = 2.0 Density = mass / volume and since the engine volume is set at 2.0 liters, then we need to that will fit 2.0 times the mass of air in the same volume. This means that we need to put twice as many air molecules in the engine. Now suppose we have a supercharger with an efficiency of 70%. This means that to achieve a density ratio of 2.0, we need a pressure ratio: P = 2.0 / 0.70 = 2.85 A pressure ratio of 2.85 equals 27 psi. If we instead look at the temperature rise … then T2 / T1 = Pressure ratio / Density ratio Then, the supercharger outlet temperatures T2 = Pressure ratio (P) / Density ratio * T1 (where the temperature is in degrees Kelvin).
Assuming an inlet temperature of 80 * F, we find that the supercharger outlet temperature is T2 = 309 * F What to think about here are intercoolers or aftercoolers … Aftercoolers are radiators that absorb heat from the after compressed air . comes out of the supercharger. The ideal intercooler dramatically cools the air temperature without drastically hindering the airflow path and therefore with minimal pressure drop. The intercooler increases power in three ways:
1 – As the air charge is cooled, the density ratio of the mixture increases at the same pressure ratio.
2 – The final temperature of the air-fuel mixture entering the engine drops, which gives a more energy-efficient combustion process (since the output power of the combustion event is directly proportional to the difference between the intake mixture temperatures and exhaust mixture temperatures).
3 – Lower the final octane requirements of the mix, allowing us to add more timing advance or more boost pressure, and generate more horsepower within the same octane limitations.
With a good intercooler, we can reduce the temperature of the air inlet charge to less than 30 degrees from the ambient air temperature. At the same time, an intercooler will only have a marginal pressure drop of 0.5 to 1.0 psi at the core. With these figures in mind, combining a Supercharger with an efficient intercooler gives us a system that has an adiabatic efficiency much closer to 100%, and this means that we can double the power of our original engine by around 18 psi of boost. (instead of 27 without the intercooler, and instead of 15 for an ‘ideal’ supercharger) if you’re interested in brushing up on the math behind the scenes.
Once you have your pressure ratio, your density ratio, your intercooler outlet temperatures, and your overall horsepower and flow numbers, most supercharger calculators can give you more detailed specifications for your car’s build-up (like exact supercharger gear figures and required intake). and exhaust dimensions, as well as fuel flow or pressure enhancement requirements). But at the heart of any supercharged or turbocharged vehicle, PV = nRT will always hold true. This is great information to know, because several people have chosen to test and sell water evacuation pumps that are normally used on ships as ‘electric’ superchargers for small displacement engines. It has been shown many times that by connecting a boost gauge to the inlet of any of these ‘electrically supercharged’ motors, these bilge pumps do not have the flow capacity or pressure lock to raise the boost pressure of the inlet mixture. in a measurable amount. . Pressure (as we explained above) is not the only indication of forced induction … but without any pressure rise, that means the ‘electric’ supercharger is 0% efficient, which means at best In cases, only heat the intake air and excess airflow will not be observed.