We analyze clustering measurements of BOSS galaxies using a simulation-based emulator of two-point statistics. We focus on the monopole and quadrupole of the redshift-space correlation function, and the projected correlation function, at scales of 0.1 โผ 60 h โ1 Mpc. Although our simulations are based on wCDM with general relativity (GR), we include a scaling parameter of the halo velocity field, ฮณ f , defined as the amplitude of the halo velocity field relative to the GR prediction. We divide the BOSS data into three redshift bins. After marginalizing over other cosmological parameters, galaxy bias parameters, and the velocity scaling parameter, we find f ฯ 8 (z = 0.25) = 0.404 ยฑ 0.03, f ฯ 8 (z = 0.4) = 0.444 ยฑ 0.025 and f ฯ 8 (z = 0.55) = 0.385 ยฑ 0.019. Compared with Planck observations using a flat ฮCDM model, our results are lower by 2.29ฯ, 1.3ฯ and 4.58ฯ respectively. These results are consistent with other recent simulation-based results at non-linear scales, including weak lensing measurements of BOSS LOWZ galaxies, two-point clustering of eBOSS LRGs, and an independent clustering analysis of BOSS LOWZ. All these results are generally consistent with a combination of ฮณ 1/2 f ฯ 8 โ 0.75. We note, however, that the BOSS data is well fit assuming GR, i.e. ฮณ f = 1. We cannot rule out an unknown systematic error in the galaxy bias model at non-linear scales, but near-future data and modeling will enhance our understanding of the galaxy-halo connection, and provide a strong test of new physics beyond the standard model.