NO NO NO!!!
there is not any set degrees per mm because of the circular action of the crankshaft.
it is a trigonometric calculation which is why you always use a special calculator to figure out the port durations
Exhaust Duration Calculator
Stroke: 40 mm
Conod Length: 90 mm
Piston Crown to Top of Barrel at TDC: .7 mm
Height over Port, Top of port to top of barrel: 26 mm
Exhause Duration (degrees): 162.14
Auto Fill Other Fields
Once you have filled in your Stroke, rod length and Crown to top of barrel above. Click Auto Fill Button.
Auto Fill to clear the fields press Clear
Transfer Duration Calculator
Stroke: 40 mm
Conod Length: 90 mm
Piston Crown to Top of Barrel at TDC: .7 mm
Height over Port:, Top of port to top of barrel 32 mm
Transfer Duration (degrees):122.83
Once you have calculated your exhaust and transfer timing click this to give;
Blowdown
Blowdown degrees:19.65
Inlet Duration Calculator for piston port motors
Stroke: 40 mm
Conrod Length: 90 mm
Piston Crown to Top of Barrel at TDC: mm .7
Piston height inlet side: 44 mm
Inlet Floor Depth, Top Barrel to Bottom Port: 56 mm
Inlet Duration (degrees):117.72
Ignition Timing in mm Before TDC Calculator
Timing Degress A:
Conrod Length: mm
Stroke: mm
mm before TDC: mm
CC Calculator
Bore: 47 mm
Stroke: 40 mm
CC = 69.4
Corrected and uncorrected compression ratios calculator
Bore: 40 mm
Stroke: 90 mm
Height over exhaust port, top of port to top of barrel 26 mm
head volume (head cc) cc 6
uncorrected 12.57 :1
corrected 8.52 :1
Two stoke oil mix calculator for %
oil %, enter your chosen oil %: %
litres of fuel: Litres
ml of oil required ml
Two stoke oil mix calculator for ratio
oil ratio , enter your chosen oil ratio (eg. for 25:1 enter 25): :1
litres of fuel: Litres
ml of oil required
This is the lambretta port calc's results now if you raise the height by one mm in the piston height inlet side feild the duration changes to 123.65 so what now your telling me that they are wrong!And this is the calc you refer to!
Exhaust Duration Calculator
Stroke: 40 mm
Conod Length: 90 mm
Piston Crown to Top of Barrel at TDC: .7 mm
Height over Port, Top of port to top of barrel: 26 mm
Exhause Duration (degrees): 162.14
Auto Fill Other Fields
Once you have filled in your Stroke, rod length and Crown to top of barrel above. Click Auto Fill Button.
Auto Fill to clear the fields press Clear
Transfer Duration Calculator
Stroke: 40 mm
Conod Length: 90 mm
Piston Crown to Top of Barrel at TDC: .7 mm
Height over Port:, Top of port to top of barrel 32 mm
Transfer Duration (degrees): 122.83
Once you have calculated your exhaust and transfer timing click this to give;
Blowdown
Blowdown degrees: 19.65
Inlet Duration Calculator for piston port motors
Stroke: 40 mm
Conrod Length: 90 mm
Piston Crown to Top of Barrel at TDC: .7 mm
Piston height inlet side: 43 mm
Inlet Floor Depth, Top Barrel to Bottom Port: 56 mm
Inlet Duration (degrees): 123.65
Ignition Timing in mm Before TDC Calculator
Timing Degress A:
Conrod Length: mm
Stroke: mm
mm before TDC: mm
CC Calculator
Bore: 47 mm
Stroke: 40 mm
CC = 69.4
Corrected and uncorrected compression ratios calculator
Bore: 47 mm
Stroke: 40 mm
Height over exhaust port, top of port to top of barrel 26 mm
head volume (head cc) 6 cc
uncorrected 12.52 :1
corrected 8.57 :1