Compression Calculator
Thread Starter
Burning Brakes
Joined: Oct 2006
Posts: 1,089
Likes: 43
From: Native Californian CALIFORNIA
Army
Compression Calculator
What is the best and most accurate compression calculator out there which is accessible free on the web. I have been using the KB-silvolite.com calculator but it seems a little high.
I am planning on using speedpro hypereutectic, do they have their own site?
I am planning on using speedpro hypereutectic, do they have their own site?
Race Director
Joined: Aug 2004
Posts: 10,628
Likes: 132
From: Duvall, WA
Silvolite is accurate enough. They take into account the important variables. The important thing is that the information you enter needs to be accurate. Things like entering the correct cylinder head volume are the key, so you actually have to cc the heads and not rely on what the manufacturer tells you for complete accuracy.
Pro
Joined: Aug 2005
Posts: 613
Likes: 2
From: West Central Florida
If your engine is apart or you rebuilt it and wrote down some specs, I can give you the formula to figure it out. (Note; approximate CR change is [-1cc = +.1cr point])
CR= Compression Ratio
C=Combustion chamber volume (in head)
P= Piston dome Volume
G= Gasket volume
V= Cylinder Stroke volume
D= Deck height volume (room above piston at TDC)
CR=(C+P+G+D+V)÷(C+P+G+D) - for dished pistons
CR=(C-P+G+D+V)÷(C-P+G+D) - for dome pistons
CR= Compression Ratio
C=Combustion chamber volume (in head)
P= Piston dome Volume
G= Gasket volume
V= Cylinder Stroke volume
D= Deck height volume (room above piston at TDC)
CR=(C+P+G+D+V)÷(C+P+G+D) - for dished pistons
CR=(C-P+G+D+V)÷(C-P+G+D) - for dome pistons
Thread Starter
Burning Brakes
Joined: Oct 2006
Posts: 1,089
Likes: 43
From: Native Californian CALIFORNIA
Army
I need some help. this is a 350 bored .040 over with 64cc heads.
What would be the Gasket bore?
What would be the cylinder bore?
Piston head volume, is this the +11.0cc you would find on the mfg spec sheet?
I understand the gasket thichness, Rod Length & Deck Clearance.
The cam states close at 30 @ 50 so I add 15 and insert 45 in the calculator.
What would be the Gasket bore?
What would be the cylinder bore?
Piston head volume, is this the +11.0cc you would find on the mfg spec sheet?
I understand the gasket thichness, Rod Length & Deck Clearance.
The cam states close at 30 @ 50 so I add 15 and insert 45 in the calculator.
Pro
Joined: Aug 2005
Posts: 613
Likes: 2
From: West Central Florida
I need some help. this is a 350 bored .040 over with 64cc heads.
What would be the Gasket bore?look up the pt. no. and view the specs, this is the diameter of the hole for the cylinder.
What would be the cylinder bore?4.040in
Piston head volume, is this the +11.0cc you would find on the mfg spec sheet?yes
I understand the gasket thichness, Rod Length & Deck Clearance.
The cam states close at 30 @ 50 so I add 15 and insert 45 in the calculator.
What would be the Gasket bore?look up the pt. no. and view the specs, this is the diameter of the hole for the cylinder.
What would be the cylinder bore?4.040in
Piston head volume, is this the +11.0cc you would find on the mfg spec sheet?yes
I understand the gasket thichness, Rod Length & Deck Clearance.
The cam states close at 30 @ 50 so I add 15 and insert 45 in the calculator.
Thread Starter
Burning Brakes
Joined: Oct 2006
Posts: 1,089
Likes: 43
From: Native Californian CALIFORNIA
Army
This is what I have :
ENTER YOUR DATA CALCULATED DATA
Cylinder Head Volume (cc) Cylinder Head Vol
(cubic in.) 03.904
Piston Head Volume (cc) Piston Head Vol
(cubic in.) 00.671
Gasket Thickness (in.) Swept Volume
(cubic in.) 44.610
Gasket Bore (in.) T.D.C. Volume
(cubic in.) 05.213
Cylinder Bore Diameter (in.) Gasket Volume
(cubic in.) 00.510
Deck Clearance (in.)
Note: Neg. nubmer above deck, Pos. number below deck Deck Volume
(cubic in.) 00.128
Stroke (in.) STATIC COMPRESSION RATIO 09.557
OPTIONAL DATA
Rod Length (in.) Adjusted Stroke (in.) 03.105
Intake Closing Point (degrees)
ABDC @ 0.050 lift plus 15 degrees DYNAMIC EFFECTIVE COMPRESSION RATIO 08.635
Does this make any good sense to you? Is a DCR of 8.635 ok for 91 octane pump gas?
ENTER YOUR DATA CALCULATED DATA
Cylinder Head Volume (cc) Cylinder Head Vol
(cubic in.) 03.904
Piston Head Volume (cc) Piston Head Vol
(cubic in.) 00.671
Gasket Thickness (in.) Swept Volume
(cubic in.) 44.610
Gasket Bore (in.) T.D.C. Volume
(cubic in.) 05.213
Cylinder Bore Diameter (in.) Gasket Volume
(cubic in.) 00.510
Deck Clearance (in.)
Note: Neg. nubmer above deck, Pos. number below deck Deck Volume
(cubic in.) 00.128
Stroke (in.) STATIC COMPRESSION RATIO 09.557
OPTIONAL DATA
Rod Length (in.) Adjusted Stroke (in.) 03.105
Intake Closing Point (degrees)
ABDC @ 0.050 lift plus 15 degrees DYNAMIC EFFECTIVE COMPRESSION RATIO 08.635
Does this make any good sense to you? Is a DCR of 8.635 ok for 91 octane pump gas?
Thread Starter
Burning Brakes
Joined: Oct 2006
Posts: 1,089
Likes: 43
From: Native Californian CALIFORNIA
Army
The copy and paste did not look good let me try this
Cylinder head volume 64cc
Piston Head Volume 11cc
Gasket thickness .039
Gasket bore (in.) 4.080
Cylinder Bore (in.) 4.04
Dech Clearance .01
Rod Length 5.7
Intake closing ABDC@50 45
SCR = 9.566
DCR= 8.643
with the silvolite calculator
Cylinder head volume 64cc
Piston Head Volume 11cc
Gasket thickness .039
Gasket bore (in.) 4.080
Cylinder Bore (in.) 4.04
Dech Clearance .01
Rod Length 5.7
Intake closing ABDC@50 45
SCR = 9.566
DCR= 8.643
with the silvolite calculator
Race Director
Joined: May 2005
Posts: 10,674
Likes: 121
From: Millington Illinois
St. Jude Donor '08-'09
The copy and paste did not look good let me try this
Cylinder head volume 64cc
Piston Head Volume 11cc
Gasket thickness .039
Gasket bore (in.) 4.080
Cylinder Bore (in.) 4.04
Dech Clearance .01
Rod Length 5.7
Intake closing ABDC@50 45
SCR = 9.566
DCR= 8.643
with the silvolite calculator
Cylinder head volume 64cc
Piston Head Volume 11cc
Gasket thickness .039
Gasket bore (in.) 4.080
Cylinder Bore (in.) 4.04
Dech Clearance .01
Rod Length 5.7
Intake closing ABDC@50 45
SCR = 9.566
DCR= 8.643
with the silvolite calculator
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Le Mans Master
Joined: Sep 2001
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From: Unreconstructed, South Carolina
Melting Slicks
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From: Florida
Last edited by jimvette999; Feb 2, 2007 at 03:48 PM. Reason: added another source w/useful info
Le Mans Master
Joined: Sep 2001
Posts: 7,739
Likes: 630
From: Unreconstructed, South Carolina
I'm NOT certain ,,, but I suspect the rbr dcr calc is in error ... that where it species you enter IVC angle @ .050" Lift ... I suspect that angle should be entered as SAE degrees & not as 0.050" degrees. Otherwise, the calc returns a very high DCR. I'm certainly NOT a DCR expert, please set me straight if I'm wrong here.
