motor cc formula

vomitspot

vomitspot

Location
mobile alabama
ok i got the formula of
bore x bore x stroke x .7854 / 1000 x the # of cylinders
does the cc of the dome get added in?
exz. 81x81x68x.7854/1000x2=700.80 cc
but if i had 33 cc domes does that have anything to do with the cc of the motor
does changing the dome cc affect the cc of the motor?
jason
 
Speedfreak

Speedfreak

Location
So. IL
I agree that the head size doesn't change the motor cc but isn't it that motor cc is the space that the piston takes up from TDC to BDC. So without ports you could fill the cylinder at BDC check the cc's and then subtract the TDC cc volume and that would be the motor cc???

WOW that sounds confusing.. is that the way it is or am I really wrong. I thought that is what cc was refering to.
 
N

njfl

X-H2
cc is more commonly referred to as displacement. Displacement is the amount of volume of air/fuel that gets, well, displaced during a cycle of rotation of the crank. Since there is nothing moving above TDC (the dome) and the dome volume remains the same between BDC and TDC, it is not included in the calculation.

Instead of remembering magic numbers and such, it might be easier to consider each bore as a geometric cylinder shape and displacement is simply the volume of a cylinder (times the number of cylinders in the motor). The height of the cylinder is the stroke and the diameter of the cylinder is the bore.
 
Proformance1

Proformance1

Liquid Insanity
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Location
New York Crew
njfl said:
cc is more commonly referred to as displacement. Displacement is the amount of volume of air/fuel that gets, well, displaced during a cycle of rotation of the crank. Since there is nothing moving above TDC (the dome) and the dome volume remains the same between BDC and TDC, it is not included in the calculation.

Instead of remembering magic numbers and such, it might be easier to consider each bore as a geometric cylinder shape and displacement is simply the volume of a cylinder (times the number of cylinders in the motor). The height of the cylinder is the stroke and the diameter of the cylinder is the bore.
Click to expand...

Perfect answer! We used to refer to it as the "swept volume".
 
Speedfreak

Speedfreak

Location
So. IL
njfl said:
cc is more commonly referred to as displacement. Displacement is the amount of volume of air/fuel that gets, well, displaced during a cycle of rotation of the crank. Since there is nothing moving above TDC (the dome) and the dome volume remains the same between BDC and TDC, it is not included in the calculation.

Instead of remembering magic numbers and such, it might be easier to consider each bore as a geometric cylinder shape and displacement is simply the volume of a cylinder (times the number of cylinders in the motor). The height of the cylinder is the stroke and the diameter of the cylinder is the bore.
Click to expand...

Yea that is what I said in all my jibberish .. I knew that someone could explain it better:biggthumpup: :biggthumpup:
 
N

njfl

X-H2
steve802cc said:
Don't remember seeing that formula before.
Here's what I use for motor displacement.

Volume = Pi x r² x height x the # of cylinders

Steve
Click to expand...

What you posted is the mathematical exact formula for volume of a cylinder. However, that is not directly applicable to tangible specs of a motor (the half-bore is never specified). Therefore, most people have the "magic" number 0.7854 which allows bore (diameter) to be used instead of radius. 0.7854 is simply pi/4, the conversion between radius and diameter.
 
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