Helpful Calculations
Immediately below is a list of the various charts/calculations on this page. Clicking
on an item in the list below will take you to the respective section of this page.
Engine Displacement Top↑
Engine displacement = bore X bore X stroke X 0.7854 X number of cylinders



Example:

Cylinder bore diameter = 4.000"



Stroke length = 3.480"



Number of cylinders = 8




Engine displacement = bore X bore X 0.7854 X number of cylinders



Engine displacement = 4.000 X 4.000 X 3.480 X 0.7854 X 8



Engine displacement = 349.8586 cubic inches (round up to 350 cubic inches)

Stroke Length
Top↑
Stroke Length = engine displacement / (bore X bore X 0.7854 X number of cylinders)



Example:

Engine Displacement = 350 cubic inches



Cylinder bore diameter = 4.000"



Number of cylinders = 8




Stroke Length = engine displacement / (bore X bore X 0.7854 X number of cylinders)



Stroke Length = 349.8486 / (4.000 X 4.000 X 0.7854 X 8)



Stroke Length = 3.480"

Cylinder Bore Diameter
Top↑
Cylinder bore diameter = square root of [engine displacement/(stroke X 0.7854
X number of cylinders)]



Example 1:

Engine Displacement = 350 cubic inches



Stroke Length = 3.480"



Number of cylinders = 8




Cylinder bore diameter = square root of [engine displacement/(stroke X 0.7854
X number of cylinders)]



Cylinder bore diameter = √[349.8486 / (3.480 X 0.7854 X 8)]



Cylinder bore diameter = 4.000"



Example 1:

NASCAR® has a 358 cubic inch maximum engine size rule. If we use a 3.480"
crank, what is biggest bore allowed?


Example 1:

Engine Displacement = 358 cubic inches



Stroke Length = 3.480"



Number of cylinders = 8




Cylinder bore diameter = square root of [engine displacement/(stroke X 0.7854
X number of cylinders)]



Cylinder bore diameter = √[358 / (3.480 X 0.7854 X 8)]



Cylinder bore diameter = 4.046"

Formula For Milling Pistons
Top↑
(For 4032 material only)
Piston dome cc's to gram conversion: 1cc (volume) = 2.8 grams (weight)


This is a good way to remove excess dome without having to recc piston: Mill a
small amount and reweight piston until total reduction is reached.



Example:

A piston has 12.5cc effective dome volume. The desired effective dome volume is
10.5cc.




To remove 2.0cc, cut 5.6 grams (2 X 2.8) from the piston dome.

Compression Ratio Top↑
Compression ratio = (swept volume + total chamber volume) / total chamber
volume


It is important that we understand two terms and their relationship to compression
ratio: Swept Volume and Total Chamber Volume. Swept Volume is the area the piston
travels through bottom dead center to top dead center. Total Chamber Volume is all
the area above the piston at top dead center. This would include the area above
the piston in the cylinder block, the area of the compressed head gasket, the combustion
chamber, the valve pocket, and the dome of the piston. The compression ratio is
the relationship of the swept volume to the total chamber volume.


To start, we need to know the Swept Volume of one cylinder. The size of one cylinder
figured in cubic centimeters.


Swept volume (cc) = cylinder bore diameter (inches) X cylinder bore diameter
(inches) X stroke (inches) X 12.8704



Example:

Cylinder head cc = 72.18 cc



Piston = flat top with two valve pockets that measure a total of 4 cc



Head gasket = 4.000" round and 0.038" thick when compressed



Deck clearance = The piston at top dead center is 0.010" below the surface
of the deck




Gasket cc = bore X bore X compressed thickness X 12.8704



Gasket cc = 4.000 X 4.000 X 0.038 X 12.8704



Gasket cc = 7.83 cc




Deck clearance volume = bore X bore X deck clearance X 12.8704



Deck clearance volume = 4.000 X 4.000 X 0.010 12.8704



Deck clearance volume = 2.059 cc




Total chamber volume = 72.18 + 7.83 + 4 + 2.059



Total chamber volume = 86.07 cc


Now we are finally ready to calculate the compression ratio!



Example:

Swept volume = 716.62 cc



Total chamber volume = 86.07 cc




Compression ratio = (swept volume + total chamber volume) / total chamber
volume



Compression ratio = (716.16 + 86.07) / 86.07



Compression ratio = 9.33:1

Total Combustion Chamber Volume For a Specific Compression Ratio Top↑
Cylinder head chamber volume = swept volume / (desired compression ratio
 1)



Example:

Swept volume = 716.62 cc



Desired compression ratio = 11:1




Cylinder head chamber volume = swept volume / (desired compression ratio
 1)



Cylinder head chamber volume = 716.62 / (11:1  1)



Cylinder head chamber volume = 71.66 cc

Cylinder Head Deck Machining To Reduce Total Chamber Volume Top↑
Cylinder head deck material removal = (current chamber volume  desired chamber
volume) X deck material per cc


By experience, we have learned that a small block Chevy cylinder head will need
0.006" deck removed for each cc we want to reduce. An open chamber big block
will take 0.005" per cc. These numbers will put us in the ballpark. Always
check by "ccing" the cylinder head chamber volume for accuracy.


Example:

Current chamber volume = 86.07 cc



Current chamber volume = 71.66 cc



Deck material removal per cc = 0.006"




Deck material to remove = (current chamber volume  desired chamber volume)
X deck material per cc



Deck material to remove = (86.07  71.66) X 0.006



Deck material to remove = 0.086"
