And school starts.... now..
I'm going to assume no knowledge of terms here so I'm sorry if I explain things already known. I'm getting the stock bore and stroke from yamaha's website (64 x 54mm). The 64mm is the cylinders diameter so to get the volume of the stroke we'll convert to centimeters and do the math.
3.1416 * 3.2^2 = 32.17 (pi * radius squared)
32.17 * 5.4 = 173.718 cc's/cylinder hence the 347cc's
If we add to that the dome size we get the total volume when the piston is at the bottom its stroke. I think the stock size is 23cc.
173.718 + 23 =196.718cc
196.718cc / 23cc = 8.5:1 hmmm..... did I do something wrong? nope it's because the actual compression ratio is calculated from the top of the exhaust port in the cylinder to top dead center. If we take the 23 ( the "1" in 6.5:1) times 6.5 we'll get the total volume once the exhaust port is cleared.
23*6.5=149.5 (149.5:23 = 6.5:1) Then if we subtract the dome volume and divide that by the initial area of the cylinder's flat circle we can get how far the stroke is in the cylinder after the exhaust port.
149.5-23=126.5
126.5/32.17=3.93 cm This tells me that the exhaust port opening in the stroke is 5.4-3.93= 1.47cm in height. Can anyone confirm that? I can't remember what it looked like when we put the cool head on my friend's banshee, but it sound about right.
Yeah, my mother always told me I should've been a math teacher! |