Calculating Compression Ratio
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Calculating Compression Ratio 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:
Where:
CR= Compression Ratio
B = Cylinder bore (Stock LT1 = 4.00in)
S = Stroke (Stock LT1 = 3.48in)
Vcc= Combustion Chamber Volume (Stock LT1 = 58cc = 3.539 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 LT1 = 0.05 in)
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 LT1 = 58cc = 3.539 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 LT1 = 0.05 in)
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)
Last edited by enisguy; Jan 17, 2005 at 10:33 PM.
Thread Starter
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From: Cleveland, Georgia
Originally Posted by seal
acording to this thing i have 19.4 compression
no wonder why math is my worst subject lol
it took me like an hour to figure out too
no wonder why math is my worst subject lol
it took me like an hour to figure out too
Check your numbers again. The formula works
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http://www.ls2.com/forums/showthread...5&pagenumber=1
a 4 page arguement about this subject, they are argueing bout how wrist pin location can make a diff etc, worth a read
a 4 page arguement about this subject, they are argueing bout how wrist pin location can make a diff etc, worth a read
Thread Starter
12 Second Club
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Joined: Dec 2003
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From: Cleveland, Georgia
Originally Posted by seal
http://www.ls2.com/forums/showthread...5&pagenumber=1
a 4 page arguement about this subject, they are argueing bout how wrist pin location can make a diff etc, worth a read
a 4 page arguement about this subject, they are argueing bout how wrist pin location can make a diff etc, worth a read
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Thread Starter
12 Second Club
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Joined: Dec 2003
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From: Cleveland, Georgia
Originally Posted by BRENTT94Z
That sucks!
This formula says I have 13.5:1 compression,
and to think I want to run boost.
This formula says I have 13.5:1 compression,
and to think I want to run boost.
Jeff
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