In the situation you described above, ya u should always call with 43% equity versus his range. That is the equation if you like, is your equity vs his range greater than the odds you are getting. Again tho, be verrry careful that the range you assign somebody is accurate, it's really easy to justify a call/fold if you assign a range that is ATC/just the nuts.

Oh and tell your friend that minraising with underpairs to fold out bluffs is not a good way to play poker In the situation u described he's better off just calling, as he's unlikely to get double-barelled by worse if he's got a nitty image.