| The basics of supercharger calculators... | | | | supercharger outlet temperature to be T2 = 309*F On |
| Supercharger calculators are based on several basic | | | | thing to think about here is intercoolers or aftercoolers.... |
| equations that govern the performance and the | | | | After coolers are radiators that wick heat away from |
| physical rules that bind superchargers. At the very | | | | the compressed air after it leaves the supercharger. |
| heart of the matter, superchargers work on the Ideal | | | | The ideal intercooler dramatically cools the air |
| Gas Law where PV = NRT Pressure x Volume = | | | | temperature without drastically impeding the air flow |
| Number of gas molecules X a constant X | | | | path and so with having a minimal pressure drop. The |
| temperature. What superchargers do, is that they feed | | | | intercooler increases horsepower in three ways: |
| the engine with more air molecules, by over feeding | | | | 1 - By cooling the air charge, the mixture's density ratio |
| the engine with forced air. This air is forced into the | | | | increases at the same pressure ratio. 2 - The final |
| engine due to the supercharger blowing more air into | | | | temperature of the air fuel mixture entering the engine |
| the engine inlet, than the engine would normally breathe | | | | drops, which gives a more power efficient combustion |
| under its own device. The result of this 'forced | | | | process (as the output power of the combustion |
| induction' can be observed and measured in one of | | | | event is directly proportional to the difference between |
| two aspects: Pressure or Temperature. In an ideal | | | | intake mixture temperatures and exhaust mixture |
| world, with a supercharger that has perfect adiabatic | | | | temperatures). 3 - Lowering the final octane |
| efficiency, we are able to feed the engine twice as | | | | requirements of the mixture, allowing us to add more |
| many air molecules (to double the horsepower figure), | | | | timing advance or more boost pressure, and make |
| by doubling the inlet air pressure (to 2.0 atmosphere or | | | | more horsepower within the same octane limitations. |
| what we call 15 pounds per square inch (PSI) of | | | | With a good intercooler, we are able to lower the |
| boost). In the real world, superchargers are not 100% | | | | temperature of the air intake charge to within 30 |
| efficient, and so it is possible that doubling the inlet | | | | degrees of the ambient air temperatures. At the same |
| boost pressure gives us less than double the | | | | time an intercooler will only have a marginal 0.5 to 1.0 |
| horsepower due to the following: | | | | psi pressure drop across the core. Having these |
| P*V=n*R*T Pressure increases by a factor of 2 | | | | figures in mind, the combination of a Supercharger with |
| Volume is fixed Number of gas molecules increases | | | | an efficient intercooler gives us a system that has an |
| by 80% (or a factor of 1.8) Temperature increases by | | | | adiabatic efficiency much closer to 100%, and this |
| a factor 11% (or a factor of 1.11) If we look at our | | | | means that we are able to make double the |
| equation above we can see: 2*P*V = 1.8*N*R* 1.11T | | | | horsepower of our original engine at around 18psi of |
| The equation is balanced as 2.0X1 = 1.8 * 1.11 (the rise in | | | | boost (instead of 27 without the intercooler, and |
| pressure is equaled by the combined effect of the rise | | | | instead of 15 for an 'ideal' supercharger) if you care to |
| in airflow and the rise in temperature). | | | | go through the math behind this scenario. |
| From here, we can also see that even at the same | | | | Once you have your pressure ratio, your density ratio, |
| 'boost' level, that a more efficient supercharger can | | | | your intercooler outlet temperatures and your overall |
| make more horsepower because more of the | | | | horsepower and flow numbers, most supercharger |
| supercharger energy is translated into compression | | | | calculators are then able to give you more detailed |
| and airflow rather than in thermal rise... So, how do we | | | | specs for your car's buildup (such as exact |
| bring these equations into the 'real world' in terms of | | | | supercharger gearing figures, and required intake and |
| horsepower and boost ? Let's start with a 2.0 liter | | | | exhaust dimensions, as well as fuel pressure or fuel |
| (volume), 140hp (air molecules) engine. Say we have a | | | | flow upgrade requirements). But at the heart of any |
| target of 280 horsepower. Our flow ratio will be | | | | supercharged or turbocharged vehicle, PV = nRT will |
| related to the ratio of our target horsepower to our | | | | always hold true. This is great information to know, |
| current horsepower.... Density ratio = 280/140 = 2.0 | | | | because several people have chosen to try and sell |
| Density = mass / volume and since the volume of the | | | | water evacuation pumps typically used on boats as |
| engine is fixed at 2.0 liters, then we need to fit 2.0 | | | | 'electric' superchargers for small displacement engines. |
| times the air mass into the same volume. This means | | | | It has been shown many times that by hooking up a |
| that we need to fit twice as many air molecules into | | | | boost gauge to the inlet of any of these 'electrically |
| the engine. Now let's assume we have a supercharger | | | | supercharged' engines that these bilge pumps do not |
| that is 70% efficient. This means that to reach a | | | | have the flow or block off pressure capability to raise |
| density ratio of 2.0 , we need a pressure ratio: P = 2.0 | | | | the inlet mixture's boost pressure by any measurable |
| 0.70 = 2.85 A pressure ratio of 2.85 is equivalent 27 | | | | amount. Pressure (as we've explained earlier) is not |
| psi. If we look instead at the temperature rise... then T2 | | | | the only indication of forced induction... but with NO |
| T1 = Pressure ratio / Density Ratio So the | | | | pressure rise at all, that means that the 'electric' |
| supercharger outlet temperatures T2 = Pressure ratio | | | | supercharger has a 0% efficiency, which means that |
| (P) / Density Ratio * T1 (where the temperature is in | | | | at best it will just heat up the inlet air and no excess air |
| degrees Kelvin). | | | | flow will be observed. |
| Assuming an inlet temperature of 80*F , we find the | | | | |