This paper measures turbulent spark ignition probability and minimum ignition energy (MIE) of the pre vaporized iso-octane/air mixture at an equivalence ratio phi = 0.8 at 373 K with Le approximate to 2.98 over a wide range of turbulent intensities (u '/S-L), where Le is the mixture's effective Lewis number and S-L is the laminar burning velocity. Ignition experiments using a fixed 2-mm electrode gap are conducted in a large dual-chamber, constant-temperature/pressure, fan-stirred 3D cruciform burner capable of generating near-isotropic turbulence. Spark discharges having nearly square voltage and current waveforms are created for accurate determination of the ignition energy (E-ig) across the electrodes. MIE = E-ig(50%) that is determined statistically from many repeated experiments at a given condition using a range of Pig to identify an overlapping energy band within which ignition and non-ignition coexist even at the "same discharge E-ig", where the subscript "ig(50%)" indicates 50% ignitability. Results show that the increasing slopes of MIET/MIEL = Gamma versus u '/SL change drastically from linearly to exponentially when u '/S-L is greater than a critical value of 4.8, which is much smaller than previous rich methane data (Le > 1) at = 1.2 with (u '/S-L)c approximate to 16 and at 0 = 1.3 with (u '/S-L) approximate to 24, revealing MIE transition. The subscripts T and L represent turbulent and laminar properties. When a reaction zone Peclet number Pe(Rz) =u 'eta(k)/alpha(Rz) is used for scaling, it is found that both present lean iso-octane and previous methane data can be collapsed onto a general correlation of Gamma(1) = 1 + 0.4P(eRz) in the pre-transition and Gamma(2), P-eR,(4) in the post-transition with the transition occurring at (P-eRZ)(c) approximate to 4.2, showing similarity on MIE transition. 71, is the Kolmogorov length scale of turbulence and alpha(Rz) is the reaction zone thermal diffusivity estimated at the instant of kernel formation. (C) 2017 The Combustion Institute. Published by Elsevier Inc. All rights reserved.