well it more to it than .3 liters over. you also change the stroke of the motor and therefore make it perform better. the other thing is that when you make a 3.0 or 3.1L engine, you also do valve work, port the head in some cases, use stronger pistons, balance everything, do the exhaust, and intake work. in the end it is costly for all the extras. if you were to just get a crank and throw it in along with some longer rods and bigger pistons, it wouldn't cost that much at all, a little more than a rebuild. with a nicely built engine you can run NOS or high boost turbo, and then youll notice the power difference.