Formulas and breakdown!
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Joined: Jul 2008
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From: alabama
Formulas and breakdown!
I wasnt sure where to post this topic!
For the guys that wonder how to figure cubic inch and compression ratios!
Cubic in formula as follows:
Bore squared multiplied by the stroke multiplied by number of cylinders mulitplied by .7854
things you have to know:
bore : the whole your piston will be going into
stroke: how far the crank will be moving the piston
cylinders: V6, V8, V10 etc
.7854 is a constant durived from 3.14 or also known as pie not the kind you eat
example of the formula in actual use! Lets use the 302 for example
4.000 X 4.000 X 3 X 8 X .7854 = 301.5936 cu in
connecting rod length has nothing to do with cu in, it just decides where the piston will stop and start in the cylinders!
Compression Ratio formula as follows:
TV/CV = C/R
TV: is total volume of the cylinder
CV: is compressed volume of the cylinder
TV: V1 + V2 + V3 + V4 + V5
CV: V2 + V3 +V4 + V5
V1: Cylinder volume use bore squared X stroke X .7854 to find volume of 1 cylinder
V2: piston to deck clearance (normally not 0) should be between .008 and .020 measured with a dial indicator.
V3: Gasket thickness find as follows bore squared X gsk thik X .7854
V4: combustion chamber volume in cc`s will be found on your head info sheet
V5: piston volume in cc`s vlv relief, dome or dish will be on your piston info sheet , a dome cc will be a +cc and will infact subtract cc`s, true flat no vlv reliefs will be 0 cc, and vlv relief will be a -cc and will infact increase cc`s, dish will be in -cc and increase cc`s aswell!
things needed to be known cc to cu in conversion 16.4cc = 1 cu in
Ok now to see it in use, I`ll use my current build for example!
V1: 4.030 X 4.030 X 3.4 X .7854 = 43.369 cu in
V2: 4.03 X 4.03 X .011 X .7854 = .14031 cu in
V3: 4.1 X 4.1 X .039 X .7854 = .5419 cu in
V4: 60/16.4 = 3.6585 cu in
V5: 6.5/16.4 = .39634 cu in
43.369 + .14031 + .5419 + 3.6585 + .39634 / .14031 + .5419 + 3.6585 + .39634
simplified 48.106/4.737 = 10.1553 10.2:1 C/R
I hope this helps the guys who often wonder how to figure these 2 things out!
For the guys that wonder how to figure cubic inch and compression ratios!
Cubic in formula as follows:
Bore squared multiplied by the stroke multiplied by number of cylinders mulitplied by .7854
things you have to know:
bore : the whole your piston will be going into
stroke: how far the crank will be moving the piston
cylinders: V6, V8, V10 etc
.7854 is a constant durived from 3.14 or also known as pie not the kind you eat
example of the formula in actual use! Lets use the 302 for example
4.000 X 4.000 X 3 X 8 X .7854 = 301.5936 cu in
connecting rod length has nothing to do with cu in, it just decides where the piston will stop and start in the cylinders!
Compression Ratio formula as follows:
TV/CV = C/R
TV: is total volume of the cylinder
CV: is compressed volume of the cylinder
TV: V1 + V2 + V3 + V4 + V5
CV: V2 + V3 +V4 + V5
V1: Cylinder volume use bore squared X stroke X .7854 to find volume of 1 cylinder
V2: piston to deck clearance (normally not 0) should be between .008 and .020 measured with a dial indicator.
V3: Gasket thickness find as follows bore squared X gsk thik X .7854
V4: combustion chamber volume in cc`s will be found on your head info sheet
V5: piston volume in cc`s vlv relief, dome or dish will be on your piston info sheet , a dome cc will be a +cc and will infact subtract cc`s, true flat no vlv reliefs will be 0 cc, and vlv relief will be a -cc and will infact increase cc`s, dish will be in -cc and increase cc`s aswell!
things needed to be known cc to cu in conversion 16.4cc = 1 cu in
Ok now to see it in use, I`ll use my current build for example!
V1: 4.030 X 4.030 X 3.4 X .7854 = 43.369 cu in
V2: 4.03 X 4.03 X .011 X .7854 = .14031 cu in
V3: 4.1 X 4.1 X .039 X .7854 = .5419 cu in
V4: 60/16.4 = 3.6585 cu in
V5: 6.5/16.4 = .39634 cu in
43.369 + .14031 + .5419 + 3.6585 + .39634 / .14031 + .5419 + 3.6585 + .39634
simplified 48.106/4.737 = 10.1553 10.2:1 C/R
I hope this helps the guys who often wonder how to figure these 2 things out!
Last edited by Venomantidote95; Mar 18, 2010 at 07:47 AM. Reason: further explination!
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