72.50mm bore +4mm crankshaft
- Thread starter 400 duster
- Start date
Well, I'm not sure what the cc means and I know that it isn't exactly 250cc, so I went with cc. That's my vote.
cylinder head deck height, combustion chamber volume, and rod length also come into play when determining exact cc's of an engine. jus saying 
http://www.cbperformance.com/v/enginecalc.html
http://www.cbperformance.com/v/enginecalc.html
It is the measurement of the swept volume that determines the capacity.
http://www.pugheaven.co.uk/ENGINE CAPACITY AND COMPRESSION RATIOS.htm
http://www.pugheaven.co.uk/ENGINE CAPACITY AND COMPRESSION RATIOS.htm
cylinder head deck height, combustion chamber volume, and rod length also come into play when determining exact cc's of an engine. jus saying
http://www.cbperformance.com/v/enginecalc.html
Deck height, head volume, and compression ratio don't have a say in displacement. They are involved in combustion chamber volume, but not all of that is displaced. If you have a square that is 1" x 1" and reciprocates 1", it will displace (1x1x1) 1ci^1. If you increase the volume above that by 10 billion cubic feet but don't change the area of the top of the piston nor the stroke, you displace the same amount.
Also, if you play around with that calculator, you can set anything to anything you want. The only fields that change CC are bore, stroke, # of cylinders.
Simple formula:
Bore x Bore x Stroke x .0007854 = displacement.
Blaster: 66 x 66 x 57 x .0007854 = 195cc
Banshee : 64 x 64 x 54 x .0007854 x 2 = 173.7 (double for 2 cylinders) = 347cc
OP's question: 72.5 x 72.5 x 61 x .0007854 = 251cc
Was looking to hear a response lol i gave a quick simple answer. Was starting to second guess myself. Can't over think it
Short answer: 3.14159 x radius x radius is the same as .7854 x diameter x diameter.
Typically, bore and stroke are given in millimeters, whereas displacement is given in cubic centimeters. Since there are 10mm in 1cm and since they are cubed, you have to account for this in the calculation. There are 1000 cubic mm in 1 cubic cm.
You can use .7854 x bore x bore x stroke for displacement. You do it this way and get cubic mm. Since we want centimeters and we're working with cubed numbers, you have to multiply the numbers of mm in a cm and then cube whatever that is. To make the entire calculation easier, you can just add that calculation in somewhere. I've always used the .7854 and gotten .0007854.
In the end, you have moved from
3.14159 x radius x radius x stroke / 1000 =
.0007854 x bore x bore x stroke
good info!! Im actually learning the same kinda stuff right now in my trig/geometry class for welding, cool to see stuff apply to real world things I'm interested in!
