im after some help on 2 things,

one is does anyone know of my Rs turbo, i am trying to find out the engine spec of it, as the owner i brought it off didn`t know anything about it, it was just a car to him.lol

the number plate is G300 S*D, is a red s2 turbo running on momo arrow rep wheels.


also when i brought it the engine was not running right, it was blowing the oil cap off and pumping smoke out of it.
i thought it was either blocked il pipe or rings gones, well cleaned all the oil pipes and breather system, and still it did it. i did a compression test and i was getting just over 100psi in 3 bores and 45psi in one bore. so this to me means the rings are gone.
well on taking the head off i had a look at the valves just to make sure they where all ok, and they seem to look fine.
the pistons on the other hand shocked me a bit, they where flat topped pistons unlike the mahle standard pistons.
what i would like to know is how can i tel if its defo a low comp bottom end or not?? the top of the piston comes flush with the top face of the block, is this the same as on the standard Turbo??

thanks for any help, im just trying to get to grips with what i have before fixing it.