i've driven both and own an si ... by the numbers both cars are pretty closely comparable ... compression ratio's, bore, curb weight, valvetrain etc. are basically the same, the only thing that caught my eye with the tc is the 163 lbs of torque versus the si's 132 ... however the driving experience is NOT comparable, i don't know what toyota did with that extra torque but you sure as hell can't feel it ... in my opinion the si is a much better drive.