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So here are my approximated values for A/F ratio, BSFC, and VE for the naturally aspirated S2000 F22C engine.
Here I’ve plotted new values for A/F ratio and BSFC for my hypothetical turbocharged S2000 vs. the car naturally aspirated. To approximate the turbocharged A/F ratio, I multiplied the NA A/F ratio by 0.95 to make it richer. To approximate the BSFC, I multiplied the NA BSFC by 1.1. These are certainly not hard fast numbers to use, but a decent approximation in the absence of real data. Of course, I made my turbocharged torque curve flat from 3000rpm to 8000rpm at 250lb-ft because you can do that with turbos by simply adjusting the pressure ratio.
So here are the values I used in the equations to calculate compressor mass flow for my hypothetical turbocharged S2000.
Using my calculated compressor mass flow, I then calculated my intake manifold pressure. To calculate the compressor pressure ratio, I had to estimate the air filter and intercooler pressure drops (delta pressure, dP). If you have one data point for pressure drop vs. mass flow, you can approximate the pressure drops at the other mass flows with the relationship: pressure drop * constant = mass flow ^2. This equation says pressure drop increases to the square of mass flow. So I used ~5kPa and ~25kPa as my data points and calculated the lower engine speed/mass flows from there.
For my ~380hp turbocharged S2000, I would go with a GTX3067R as my 250lb-ft of torque from 3000rpm to 8000rpm fits nicely on the compressor map. Notice that the compressor PR is ~2.0 where the actual intake manifold pressure is ~10.1psi. This is due to the pressure drops from the air filter and intercooler.
The Garrett Boost Advisor is the quick and dirty turbo matching app if you have limited data. Using the Garrett Boost Advisor, let’s plug in a couple of my values. There is a fault in this app in that it does not allow a VE greater than 1.0. Modern gasoline engines often have VEs better than 1.0 (100%).
Plugging in my hypothetical values, the Garrett Boost Advisor cranks out similar values as it should. Of course, the pressure ratio is a little off due to the VE value not being the same. There is no GTX3067R compressor map in the Boost Advisor, so I used the GTX3071R compressor map. If I were looking to maximize peak power, the GTX3071R would be a better option as the peak power point is in a high efficiency spot on the compressor map. But I would pick the GTX3067R for better spool-up and mid-range.
