Displacement Formula

When customers come in needing a top end bored to an oversize piston, I am often asked, "What will the displacement be?" I have tended to say, "oh, maybe about a couple of cc's more than stock." That is really a lame answer, so I wrote this little program to quickly spit out the answer. After entering the number of cylinders and the stroke, different bore sizes can be entered and their corresponding displacements seen.

Thanks to Ron West, we have simplified the process. So just plug in your numbers and go!
(if you are using netscape, this will not work, sorry)

# of Cylinders
Bore (mm)
Stroke (mm)

Displacement (cc)

Common Stroke Measurements
*Bike*	*stroke (mm)*
YSR 50	39.2
TZM50	47.8
NSR50	41.4
NS 50	41.4
MB5	41.4
RM 80	'89 on 46.8
CR 80
YZ 80	"93 ob 47.8
XR 100	45

Formula for computation developed by Jonathan Teraji of Team Calamari

This can also be written in Q basic.

DEFSNG A-Z
CONST pi = 3.14159
g = 1
f = 1
WHILE g = 1
j = 1
CLS
LOCATE f, 1
INPUT "# of cylinder "; n
INPUT "input stroke in mm "; h
PRINT "input bore in mm "
WHILE j = 1
LOCATE f + 2, 21
INPUT d
x = pi * (d / 2) ^ 2 * h * n / 1000
LOCATE f + 2, 30
PRINT x; "cc"
LOCATE 20, 20
PRINT "press any key to change bore or to quit or to start again",

INPUT q$
IF q$ = "q" THEN
END
ELSEIF q$ = "a" THEN
j = 2
END IF
f = f + 1
WEND
f = 1
WEND

So...copy this into your computer and plug in numbers and see how various bore sizes affect the displacement, or use the calculator above if your not into math!

That's it for this month, shoot me some E-mail if you have specific YSR questions and I'll do my best to answer them as time allows, and/or suggestions for topics in "Tech Tips!" Remember this page is for you!

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