Piston volume
#1
Intermediate
Thread Starter
Piston volume
I am trying to determine what compression ration I have but I can’t seem to find out what kind of pistons I have( came in car already). Does anyone know how to calculate the + or - volume on piston tops ? I have a 4.155 bore, 4.125 stroke with stock LS7 heads ( 70cc combustion chamber ) I just don’t know what pistons I have and how to measure them so I can see what CR I have . Thanks
In advance
In advance
#2
How precise do you need to be? You can probably estimate pretty well the Clearance Volume at Top Dead Center using a pair of dial calipers.
#3
I'll take a stab at this. My numbers seem really high, but we can use this to get the conversation moving.
V_d = Displacement Volume
V_d = (pi/4)(b^2)(s) = 55.931in^3
where
b = Bore = 4.155 in
s = Stroke = 4.125 in
Compression Ratio = (V_d + V_c) / (V_c)
where
V_c = Clearance Volume = Combustion Chamber Volume = 70cc = 4.272in^3
Compression Ratio = 14.093:1
Again this seems really high so this is either a high performance motor or I'm bad a math.
V_d = Displacement Volume
V_d = (pi/4)(b^2)(s) = 55.931in^3
where
b = Bore = 4.155 in
s = Stroke = 4.125 in
Compression Ratio = (V_d + V_c) / (V_c)
where
V_c = Clearance Volume = Combustion Chamber Volume = 70cc = 4.272in^3
Compression Ratio = 14.093:1
Again this seems really high so this is either a high performance motor or I'm bad a math.
Last edited by Will_M1911; 12-17-2019 at 03:59 PM.
#4
Intermediate
Thread Starter
#5
Intermediate
Thread Starter
I'll take a stab at this. My numbers seem really high, but we can use this to get the conversation moving.
V_d = Displacement Volume
V_d = (pi/4)(b^2)(s) = 55.931in^3
where
b = Bore = 4.155 in
s = Stroke = 4.125 in
Compression Ratio = (V_d + V_c) / (V_c)
where
V_c = Clearance Volume = Combustion Chamber Volume = 70cc = 4.272in^3
Compression Ratio = 14.093:1
Again this seems really high so this is either a high performance motor or I'm bad a math.
V_d = Displacement Volume
V_d = (pi/4)(b^2)(s) = 55.931in^3
where
b = Bore = 4.155 in
s = Stroke = 4.125 in
Compression Ratio = (V_d + V_c) / (V_c)
where
V_c = Clearance Volume = Combustion Chamber Volume = 70cc = 4.272in^3
Compression Ratio = 14.093:1
Again this seems really high so this is either a high performance motor or I'm bad a math.
#6
Racer
This may or may not work with the engine in the car, but you should be able to seal off the top of the piston with a plexiglass plate and grease, then use a burette and water to determine the volume of the piston. If the piston is in the hole it gets trickier, but can still be done by sealing the piston walls, and doing more math, but could lead to getting some water down the piston walls and into the pan. It looks like there are plenty of videos online for "how to cc a piston dish".