I asked the dealer about the venturis and he told me it should not be used to increase power but to improve thrust curve in the mid range. I have always liked the response of my 140DZ but if it can get better why not. I have allways liked shiny polished aluminum parts especially small ones which are ment to do great things

140dz: 9mm or 10mm
160dz: 8mm 8,5mm or 9mm

He told me the two engines have different type of 'needs' and that is why the sizes differ.