Exhaust port 65%
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If we say that an exhaust port should measure 65% of the diameter of the cylinder and we know that the diameter is 69 mm, so that 65% would be 44.85 mm. How do we measure these 44.85 mm? Directly in the cylinder in a straight line from side to side of the port? Or we draw the port on a paper and then curve the paper into the cylinder? There is a big difference
- jonny snatchsniffer
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straight across in a direct line from edge to edge
- coaster
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I believe that it applies to the curved measurement not the cord (straight line), you need to roll up a sheet of paper and tape insid the bore and then do a 'rubbing' with a pencil to get the outline to the port then roll it out flat and measure with a ruler.santacama wrote:If we say that an exhaust port should measure 65% of the diameter of the cylinder and we know that the diameter is 69 mm, so that 65% would be 44.85 mm. How do we measure these 44.85 mm? Directly in the cylinder in a straight line from side to side of the port? Or we draw the port on a paper and then curve the paper into the cylinder? There is a big difference
I've been doing a lot of this lately
- coaster
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I have a 225 barrel that measures 45mm across the Chord (straight line) which has snapped the bottom ring after less than 700 fairly gentle miles, ita's 55mm measured around the circumference which would equate to about 78% I thinkjonny snatchsniffer wrote:straight across in a direct line from edge to edge
Happy to learn more on this subject
- jonny snatchsniffer
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if you have good wire rings you can go to 70% of bore or more with a good shape port but they will need changing more often
45mm with cast rings should be ok on a 70 mm bore, chamfer the port edges
45mm with cast rings should be ok on a 70 mm bore, chamfer the port edges
- sean brady scooters
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the %age of port widths that you can safely go to and use is crucial and greatly dependant on the quality of parts used...
much depends on not only the quality of pistons and ring pegs but also on the quality of the rings and their spec ,the thinner they are and deeper section they are as well as their materials dictates how far you can safely go on port widths
also the shape of the ports themselves have a serious factor in the equation of performance/reliabity
whenever I widen an ex port ,i do it as a % age around the bore and not chord/straight across.
much depends on not only the quality of pistons and ring pegs but also on the quality of the rings and their spec ,the thinner they are and deeper section they are as well as their materials dictates how far you can safely go on port widths
also the shape of the ports themselves have a serious factor in the equation of performance/reliabity
whenever I widen an ex port ,i do it as a % age around the bore and not chord/straight across.
Sean Brady Scooters - 01765 690 698
- sean brady scooters
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sorry but I thought i,d made it plain....around the bore/curve
Sean Brady Scooters - 01765 690 698
Taffspeed use to measure theirs straight across.