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10-18-2002, 01:47 AM | #1 |
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Location: Portland Oregon
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Help determine static compression ratio
I have 62 CC heads
I have 20 CC dishes on my pistons I have a head gasket that compresses to .039 inches I have piston to deck clearance of .025 inches I have a 4.030 bore I have a 3.5 inch stroke Anyone know the calculation to determine the static compression ratio?
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1966 Customized for daily street and highway domination. 358 Windsor running 425 HP C-4 Auto and 3.25 Posi |
10-18-2002, 11:12 AM | #2 |
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Using my weak math skills, I come up with 11.3:1. I did most of this in my head, but it should be close. I will try and come up with a more precise answer later when I have a little more time (math gives me headaches).
Take care, ~Chris
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Webmaster: Rice Haters Club Jim Porter Racing Peckerwoods Pit Stop Support Your Local
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10-18-2002, 11:52 AM | #3 |
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I'm not that good at math myself either..but i came up with 11.5:1?? Sounds about right i guess.
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68 Camaro Gene Fulton 632ci Two stages of Jug 8.41 164mph Rockingham 1-26-03 |
10-18-2002, 12:02 PM | #4 |
or '331 LX Eric'
Join Date: Jan 1999
Location: Columbus, Ohio
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I thought that dish pistons were for lower compression and that dome pistons were for higher compression? If so, 11.3-11.5 sounds too high. I was thinking more in the area of 9.3 or 9.4:1 compression.
E
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1991 5.0 LX Coupe - 40,750 miles 331 cu. in. / Tremec 3550 / BFG Drag Radials 12.22 @ 114.31 mph - w/1.89 60' |
10-18-2002, 06:05 PM | #5 |
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Well, so much for doing it in my head. I just sat down with the numbers and a calculator, and came up with 8.4:1 compression. Here are my notes:
Compression equals Cylinder Volume plus Chamber Volume divided by Chamber Volume. So: 731.3351 + 99.033001 = 830.3681 830.3681 / 99.033001 = 8.3847615:1 (or, 8.4:1) Cylinder Volume: 731.3351cc Chamber Volume: 99.033001cc 62 + 20 + 6.6535166 + 10.379485 = 99.033001cc Combustion Chamber Volume: 62cc Valve Reliefs/Dish: 20cc Piston to Deck .025": 6.6535166cc Head Gasket .039": 10.379485cc
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10-18-2002, 09:51 PM | #6 |
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Man my math skills are BAD. I think i saw where i made my mistake though.. DOH.
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68 Camaro Gene Fulton 632ci Two stages of Jug 8.41 164mph Rockingham 1-26-03 |
10-19-2002, 01:22 PM | #7 |
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Thanks for the help.
Some of the deck hight goes away as the rod grows under temp, and my heads were shaved, so I figure I lost some cc's. Even so, the final compression ratio should not exceed 8.5-9.0. In the future, I should be able to strap on a super charger without any worries--other than having an INSANE ride.
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1966 Customized for daily street and highway domination. 358 Windsor running 425 HP C-4 Auto and 3.25 Posi |
10-20-2002, 01:26 AM | #8 |
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Hey Peckerwood,
I went back and remeasured all the important stuff. Head gasket compressed will be .039. Deck is actually .018 inches. Dish measured at 15 CC. The original combustion chamber was 64 CC but the head was shaved 0.1 inches. The shop told me it would raise me about 1/2 a compression point..... I figure the volume is somewhere between 59 and 62 CC I used the EZ Engine Analyzer to calculate compression ratio. This is what it said. 8.96 to 1 at 62 CC or 9.51 at 59 CC. Thanks for the help. You were right on with your second calculation based on my original data. At 9.5 to one compression I will probably need a water injector if I strap on a supercharger. Oh well, I love steam cleaning my exhaust and combustion chambers anyway. You have to just love today's pump gas........
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1966 Customized for daily street and highway domination. 358 Windsor running 425 HP C-4 Auto and 3.25 Posi |
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