Journal of Applied Sciences1812-56541812-5662Asian Network for Scientific Information10.3923/jas.2012.161.167MashkourMahmoud A.22012122An analytical solution to estimate the effective diameter of a naturally aspirated internal combustion engine intake pipe is presented in this paper. A formula to predict the effective diameter for the geometry of the intake pipe as a function of cylinder bore, stroke, engine speed, pipe length, ambient temperature and aerodynamic losses, is created. In this analysis, the kinetic energy of a charge column in the period of a filling cylinder and the maximum kinetic energy are taken into consideration. A comparison between the results of the novel suggested formula and the actual published work to determine the intake pipe diameter is done for different engines. The results indicated that a good agreement to estimate the intake pipe diameter, especially in high-speed engines is obtained.]]>Heywood, J.B.,2002Ferguson, C.R. and A.T. Kirkpatrick,2001Pearson, R., M. Bassett, P. Virr and S. Lever,2006Tabaczynski, R.J.,1982Taylor, C.F., J.C. Livengood, D.H. Tsai,1955Estop, T.D. and A. McConkey,2009Benson, R.S.,1982Eberhard, W.W.,1971