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Author Topic:   compression calculation
65driver
Gearhead

Posts: 216
From: Syracuse, NY
Registered: Feb 2000

posted 03-04-2002 06:03 PM     Click Here to See the Profile for 65driver   Click Here to Email 65driver     Edit/Delete Message   Reply w/Quote
If I have 9:1 compression, with a 64cc head, on a 289 thats been bored 30over, how do I calculate my compression if I switch to a 60cc head or a 58cc head?

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capri man
Gearhead

Posts: 7611
From: doerun, ga.
Registered: Nov 2000

posted 03-04-2002 08:15 PM     Click Here to See the Profile for capri man   Click Here to Email capri man     Edit/Delete Message   Reply w/Quote
try this 65driver.

http://www.kb-silvolite.com/calc.phtml#comp1

------------------
mike r
racing is real
everything else is just a game.
81 capri-7.56 @88mph 1/8
1.56 60 ft.

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Ron
Gearhead

Posts: 137
From: Newcastle, Wa.
Registered: Feb 2002

posted 03-05-2002 12:39 AM     Click Here to See the Profile for Ron     Edit/Delete Message   Reply w/Quote
quote:
Originally posted by 65driver:
If I have 9:1 compression, with a 64cc head, on a 289 thats been bored 30over, how do I calculate my compression if I switch to a 60cc head or a 58cc head?

Work the math backwards
9 X 64 = 576 - 64 = 512
so 512 is your starting point
now lets go with the 58 cc head
512 + 58 = 570 divided by 58 = 9.83

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n2oMike
Gearhead

Posts: 2831
From: Spencer, WV
Registered: Jan 2001

posted 03-05-2002 09:52 AM     Click Here to See the Profile for n2oMike   Click Here to Email n2oMike     Edit/Delete Message   Reply w/Quote
First off, you don't have 9 to 1 with a 64cc head on a flattop 289. It's around 8.4

swept volume = 600.3 cc
clearance = valve notches + deck + gasket + chamber

clearance = 4 + 4.2 @ 0.020" deck + 9 + 64
clearance = 81.2 cc

cr = (swept + clearance)/ clearance
cr = (600.3 + 81.2)/81.2
cr = 681.5/81.2
cr = 8.4

w/60 cc head

cr = (600.3 + 77.2)/77.2
cr = 8.78

w/58 cc head

cr = (600.3 + 75.2)/75.2
cr = 8.98

Most people over estimate their compression ratios by not taking all the variables into account.

Good Luck!

------------------
Mike Burch
66 mustang real street
302 4-speed 289 heads
10.63 @ 129.3
http://www.geocities.com/carbedstangs/cmml_mburch.html
http://www.fortunecity.com/silverstone/healey/367
http://www.mustangworks.com/cgi-bin/moi-display.cgi?220

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65driver
Gearhead

Posts: 216
From: Syracuse, NY
Registered: Feb 2000

posted 03-05-2002 08:27 PM     Click Here to See the Profile for 65driver   Click Here to Email 65driver     Edit/Delete Message   Reply w/Quote
Hey, thanks for all the info!

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