Been out of school awhile and can not remember the formula for figuring displacement. Anyone remember?
Tim

I think its pie r2*stroke

Been out of school longer than I thought, because you lost me.
Tim

PIE X radius squared x length = the volume of a cylinder
PIE= 3.1428

Find Pi on your calculator, or just use 3.14159

Take half the bore, that's r (the radius)

Then the displacement is Pi times r times r times the stroke

Displacement = pi x r x r x stroke

If you use mm, the answer will be in cubic mm, divide by 1000 to get cc (cubic centimeters)

If you use inch, the answer will be in cubic inches

Good luck!
Dave Olson

No, actually 3.1428 is 22/7. That only approximates Pi.

A calculator will show 3.1415927 if you punch the pi button, and that's an approximation.

3.142 is close enough for this, though.

Just being picky,
Dave Olson

Got It! Thanks Guys.
Tim

Hey Dave tlar. approx works for me. My cheap calc dont have a pi button. LOL

Scar & Bearmech - you're both right, and you're both wrong

Bearmech is talking about Pie and Scar is talking about Pi. One is a food, the other is a number.

My calculator show Pi as 3.1415926535897932384626433832795 (Windows calculator in scientific mode), but that's still only an approximation. Scientists still haven't been able to calculate the value of Pi to it's final decimal point.

3.1416 is close enough for me.

I have always had a question in my mind about the truc displacement calculation on two stroke engines. For a four stroke, the bore cross sectional area times the stroke is correct. But on a two stroke, should you subtract the exhaust opening from the stroke to get the "true" displacement? I know that the common practice is bore cross sectional area times stroke including the exhaust opening.

Just wondering.

2 and 4 strokes are measured the same. to many varibles with the ex port. Just by using a tuned pipe as opposed to an open ex messes up the exhaust displacement theory.

Not to belabor the math but...

Pi does not have a final number, it goes on forever.

http://grapevine.abe.msstate.edu/~ft.../cylinder.html

That depends which scientists you want to listen to. Some theorize it has an ending, some theorize it eventually becomes a repeating decimal.

And if you can "think outside the box", where 3 parallel lines intersect at infinity, then Pi should resolve to a final decimal after an infinite number of decimal points.

But we digress...

Numbers like Pi and e belong to a category called transcendental number. Even though the series are infinite, you can calculate them precisely to as many decimal places as you care to. Many have done just this first manually and later with computers to a gazillion number of decimal places. There are even competitions for people who can recite the longest Pi decimals - a genuine waste of brain cells IMHO.

As to how many decimal places you need for your calculation, you need simply ask yourself how many significant digits you require for your final answer and how precise you bore and stroke measurements are. You only need as many SD as you want in the final answer. For example, if all you want to do is to see if your engine is a 2.8 c.i. or 50cc then even 3.1 would work just fine for Pi. Plus, if your bore and stroke numbers carry no more precision than, say, 45.0mmx31.0mm, then you really only need 3.14 for Pi for a final answer of no more precision than 49.3cc.

Of course, more decimal places for Pi doesn't hurt your calculations; it just won't make the answer any more precise than your other operands.

Okay, have we peaked the geek meter already?

OH MY HEAD HURTS

FWIW
Bore x Bore x .7854 x stroke = Dissplacement in cubic inches

example:
Fox .60 bore= .906 stroke= .937
.906 x .906 x .7854 x .937 = .604 ci

Phred