This calculator will help you choose the right Turbo Charger in conjunction with a Compressor Map. We recommend Garrett Turbochargers. One assumes you will be looking at Garrett Compressor maps in lb/min. If you look at other manufacturers you may need to convert from other units of measurement.

Imperial measurements with regard to engine tuning can be very helpful and easy to understand. For example, you will notice that air mass in lb/min is roughly equal to peak HP divided by 10. Or look at it another way, find the compressor map figure, in the middle of the island, where the turbo is at its most efficient. Look at the Air mass figure, multiply that by 10 and you have a clear idea of the power capability of the turbo at maximum efficiency.  In this case approx 300HP. Looking at the GT2871 - sure you can get more. This GT2871R map indicates that a pressure ratio of 3 will deliver 400HP. 

Enter the capacity in CC, together with the RPM that peak power will occur at. Then enter the boost figure that will occur at that peak RPM figure. Most Turbo engines run higher pressure ratios at lower RPM. This calculator is designed to size a compressor based on Air consumption in lbs a minute at Wide Open Throttle at peak RPM. However you could used it to work out how much power you can make at much lower RPM if you are limited to a peak HP figure. WRC cars make good use of this by making 300HP pretty much continuously ! Leave VE and BSFC alone. One exception might be to tweak VE to "tune" the calculator to a naturally aspirated base HP figure. Some naturally aspirated engines can achieve more than 100% VE.