Compression formula Helppp?
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Joined: Feb 2001
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From: IN, USA
Compression formula Helppp?
What is the formula to find the comression ratio. I can't seem to figure it out. I have a 350 (.030 over),the pistons are .125 domed, the the deck height is .030 ,the head gasket is .031, and the heads are 67cc. Everytime I try and figure it it comes out to around 9.8:1 and I know it is higher than that. I would apreciate all the help you all can give. Thanks
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From: 51°N 114°W, 3500'
Car: 87 IROC L98
Engine: 588 Alcohol BBC
Transmission: Powerglide
Axle/Gears: Ford 9"/31 spline spool/4.86
You need to find out how much that .125 dome displaces in cc's or the formula will be wrong.
(bore x bore x stroke x 0.7854 + deck height(negative number if piston is below the deck) + head gasket volume + combustion chamber size less dome volume) / (deck height + head gasket volume + combustion chamber size less dome volume)
Dome volume isn't usually included with piston specs on dome pistons but you can find out roughly what it is with a little work. Make a clay impression of the top of the piston. Fill the dome impression with water then measure the water volume.
If you had flat top pistons with the typical 6cc total valve reliefs, that engine would be 9.486:1
------------------
Follow my racing progress on Stephen's racing page
and check out the race car
87 IROC-Z Pro ET Bracket Race Car
383 stroker (carbed) with double hump cast iron heads and pump gas
461 Big Block installed and ready for the 2001 racing season
Best results before the 383 blew up
Best ET on a time slip: 11.857 altitude corrected to 11.163
Best MPH on a time slip: 117.87 altitude corrected to 126.10
Altitude corrected rear wheel HP based on power to weight ratio: 476.5
Best 60 foot: 1.662
Racing at 3500 feet elevation but most race days it's over 5000 feet density altitude!
Member of the Calgary Drag Racing Association
87 IROC bracket car, 91 454SS daily driver, 95 Homebuilt Harley
[This message has been edited by Stephen 87 IROC (edited March 09, 2001).]
(bore x bore x stroke x 0.7854 + deck height(negative number if piston is below the deck) + head gasket volume + combustion chamber size less dome volume) / (deck height + head gasket volume + combustion chamber size less dome volume)
Dome volume isn't usually included with piston specs on dome pistons but you can find out roughly what it is with a little work. Make a clay impression of the top of the piston. Fill the dome impression with water then measure the water volume.
If you had flat top pistons with the typical 6cc total valve reliefs, that engine would be 9.486:1
------------------
Follow my racing progress on Stephen's racing page
and check out the race car
87 IROC-Z Pro ET Bracket Race Car
383 stroker (carbed) with double hump cast iron heads and pump gas
461 Big Block installed and ready for the 2001 racing season
Best results before the 383 blew up
Best ET on a time slip: 11.857 altitude corrected to 11.163
Best MPH on a time slip: 117.87 altitude corrected to 126.10
Altitude corrected rear wheel HP based on power to weight ratio: 476.5
Best 60 foot: 1.662
Racing at 3500 feet elevation but most race days it's over 5000 feet density altitude!
Member of the Calgary Drag Racing Association
87 IROC bracket car, 91 454SS daily driver, 95 Homebuilt Harley
[This message has been edited by Stephen 87 IROC (edited March 09, 2001).]
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Joined: Apr 2000
Posts: 223
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From: Wilmington, IL Age: 35
Killer,
Check this Compression Ratio Calculator out. It should give you a pretty good idea of what's up.
http://www.prestage.com/carmath/calc_compression.asp
------------------
86 Trans Am WS6 Black with tinted windows, shaved door handles
ZZ4, Mini-ram, true duals
***Too many other mods to mention***
"In the future, cities will become deserts,
roads will become battlefields, and the hope of mankind
will appear as a stranger" The Road Warrior
Check this Compression Ratio Calculator out. It should give you a pretty good idea of what's up.
http://www.prestage.com/carmath/calc_compression.asp
------------------
86 Trans Am WS6 Black with tinted windows, shaved door handles
ZZ4, Mini-ram, true duals
***Too many other mods to mention***
"In the future, cities will become deserts,
roads will become battlefields, and the hope of mankind
will appear as a stranger" The Road Warrior
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