CA18DET version lighter than the SR20DET version? that doesn't make sense. since the CA18DET is made out of iron it should be heavier than the SR20DET because the SR20DET is made out of aluminium. even though the SR20DET is .2L bigger than the CA18DET, the SR is made out of aluminium so that .2L difference in size shouldn't make up the weight difference and make it heavier because aluminium is lighter that iron, right?