Tumble flow has been recognized as an important and positive enhancement of combustion for SI engines. Tumble flow modeling with quasi-dimensional models is difficult because of the transient nature of tumble vortex, compared with swirl flows. Although multi-dimensional models have obtained plenty of attention recently in engine research, quasi-dimensional SI engine models will continue to dominate industrial applications in the near future. In the present research, a bulk flow model has been developed for tumble flows based on angular momentum conservation. Its effect on turbulence was then modeled using a Two-Equation Model (k-ε Model). A methodology has also been developed to use particle tracking velocimetry (PTV) measurement to calibrate the quasi-dimensional bulk flow model at engine BDC to model tumble vortex and tumble-generated turbulence. The Entrainment Combustion Model was used for combustion modeling. A 1.6L 14 4-valve and a 6.8L V 10 3-valve research engines were used for model validation. Results showed that the model can predict early burn duration to within 1-2 CA of experimental data, which is considered good for engine codes. Engine analysis with the model also suggested that the effect of tumble on combustion rate is not linear. The methodology developed in the present research is a powerful and efficient tool for up-front engine analysis and development.