Post by metalbeast on Aug 30, 2005 10:06:33 GMT -5
Compression ratio is a term that all of us are familiar with, but very few of us really understand. Whether we are milling down stock heads, swapping for some aftermarket ones, changing the stroke, the pistons or just simply using a thinner head gasket, changes to you engine combo have a profound affect your compression ratio and, consequently, on overall performance and drivability. With that in mind, I developed and easy to use formula to calculate compression ratio.
Compression ratio is defined as "the volume of the cylinder at BDC (bottom dead center) divided by the volume of the cylinder at TDC (top dead center).
CR = (Vbdc/Vtdc)
Without getting into too much detail, we can expand this to the following equation:
CR = [{(B/2)^2 * S*Pi}+Vcc+Vp+{(B/2)^2*Pi*(DH+TG)}]
[{(B/2)^2*Pi*(DH+TG)}+Vcc+Vp]
Where:
CR= Compression Ratio
B = Cylinder bore (Stock LT1 = 4.00in)
S = Stroke (Stock LT1 = 3.48in)
Vcc= Combustion Chamber Volume (Stock Aluminum Head LT1 = 58cc = 3.539 in3; Stock Iron Head LT1 = 64cc = 3.905 in3)
Vp= Piston Volume (Stock LT1 = 4.5cc = 0.274606 in3)
DH = Deck Height (Stock LT1 = 0.015 in)
TG = Head Gasket Crush Thickness (Stock Aluminum Head LT1 = 0.05 in; Stock Iron Head LT1= 0.029in)
Pi = 3.1415
As long as all other variables remain constant, you can change a single variable (for example larger/smaller combustion chamber size) to determine your new Compression Ratio.
*Convert Cubic Cenimeters (ccs) to Cubic Inches (in^3) using the following formula
in^3 = (CCs/16.387064)
Compression ratio is defined as "the volume of the cylinder at BDC (bottom dead center) divided by the volume of the cylinder at TDC (top dead center).
CR = (Vbdc/Vtdc)
Without getting into too much detail, we can expand this to the following equation:
CR = [{(B/2)^2 * S*Pi}+Vcc+Vp+{(B/2)^2*Pi*(DH+TG)}]
[{(B/2)^2*Pi*(DH+TG)}+Vcc+Vp]
Where:
CR= Compression Ratio
B = Cylinder bore (Stock LT1 = 4.00in)
S = Stroke (Stock LT1 = 3.48in)
Vcc= Combustion Chamber Volume (Stock Aluminum Head LT1 = 58cc = 3.539 in3; Stock Iron Head LT1 = 64cc = 3.905 in3)
Vp= Piston Volume (Stock LT1 = 4.5cc = 0.274606 in3)
DH = Deck Height (Stock LT1 = 0.015 in)
TG = Head Gasket Crush Thickness (Stock Aluminum Head LT1 = 0.05 in; Stock Iron Head LT1= 0.029in)
Pi = 3.1415
As long as all other variables remain constant, you can change a single variable (for example larger/smaller combustion chamber size) to determine your new Compression Ratio.
*Convert Cubic Cenimeters (ccs) to Cubic Inches (in^3) using the following formula
in^3 = (CCs/16.387064)
