Hello everybody, I am working on the whole vehicle calculations, engine, brakes, suspension and engine simulation, using that software, take a look: http://www.speed-wiz.com/calculations/engine-simulation/engine-simulation-conditions.htm That software, you input the values at the top, and it calculates and outputs the results shown in the bottom of the screen my work is to get the formulas which are used to get those ouputs, and i am just stuck with the intake air density, of those inputs in the screen i sent. well, here are the formulas i used for "outside air density" calculations, and it gave me 0.0771 Ibs/cubic.ft, see how i got it, to help you understanding what i am requiring, for the "intake air density". 3- outside air density: By substituting in the formula: Density = P / (R * T) Where p: is the outside air pressure (Ibs/inch^2), R: is the Gas constant = 53.35 (ft-lb)/ (lbm•R), and T: is the outside air temperature in °R, And to convert P from (Ibs/inch^2) to (Ibs/ ft^2), we divide by (0.083) ^2, so we get: Air pressure P = 14.68 /.083^2 = 2130.933 (Ibs/ft^2), so we get: Density = 2130.933/ (53.35*518.67) = 0.077I Ibs/cf. i am sure we will use same formula, but how can i calculate or get the intake air pressure to substitute in that formula, as the R is known, and T: is the intake air temperature is given as 80 F in the inputs. hope anyone familiar with internal combustion engines help me with that, will appreciate your help a lot, Thanks.