| with the most respect possible, if one asks these questions, its likely that one really should not be doing these type of mods.
"changing the pistons" as you mention is pretty vague. the E36 M3 is already running a 10.5:1 piston, and as such much more will play with your knock sensors, and your ability to perform on pump gas.
if you mean you want to bore the thing, i see no purpose in doing that on these cars, unless the cylinder wall has been damaged.
If you are going for a certain sound, the exhaust has more control over the tone of the car, but cams rather than pistons have a more drastic effect on how the car sounds. you can rest assure that any internal engine mod will effect the sound the car makes.
In terms of a power adder.. the question as to whether its OK to turbo a 100k mile M3 depends on the specific car, and the condition of everything.
i would concentrate on finding the right car first.. then work out the mods.
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