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compression ratio
On a 3.3 motor with stock pistons (97 mm) that have had the edge milled (to clear head) acting on a 3.6 crank, what would the compression ratio be? Keep in mind that the 3.6 crank is 2mm longer stroke.
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Kris @ Tech9 86' 930/GT-40R Sold  94' Rustang GT daily (long gone) 2008 C6/Z51 Corvette |
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03-31-2007, 06:01 PM
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Just the displacement increase alone would yield 7.63. However, the unknown is the volume remaining that was not machined off to clear the head. Chances are, the actual result would be higher.
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'77 930 turbo Garretson I/C 1 BAR spring, (2) '82 Triumph Bonneville Royal Wedding Edition Past rides: '74 914 1.9 liter twin plugged track car, '83 928S, '87 924S, '75 911S w '78 ROW 3.0, '72 911T, '70 911T and various other insignificant domestic examples. Happiness is a grey tailpipe! Turbo lag......it's worth the wait! |
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03-31-2007, 08:35 PM
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so you dont think that it would be high compression like 9 or 10:1? The pistons only had the edges milled down to clear the heads.
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Kris @ Tech9 86' 930/GT-40R Sold 94' Rustang GT daily (long gone) 2008 C6/Z51 Corvette |
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04-01-2007, 05:15 AM
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My 3.4 with 98 mm pistons with the new 3.6RS crank resulted in a compression ratio of 7.72
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Olli Selander 1989 930 - 3.5l - M48 - G64/51 |
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04-01-2007, 07:18 AM
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Oms, What piston crown hieght did you use? Did you get custom pistons?
I need to get the exact formula in order to calculate it.
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Kris @ Tech9 86' 930/GT-40R Sold 94' Rustang GT daily (long gone) 2008 C6/Z51 Corvette |
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04-01-2007, 11:19 AM
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Quote:
http://forums.rennlist.com/rennforums/showthread.php?t=325101
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Olli Selander 1989 930 - 3.5l - M48 - G64/51 Last edited by oms930; 04-01-2007 at 02:08 PM.. |
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04-01-2007, 01:54 PM
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Thank you, that was very informative- Im thinking the C/R will not be that high which will leave nice room for boost to be squeezed in there.
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Kris @ Tech9 86' 930/GT-40R Sold 94' Rustang GT daily (long gone) 2008 C6/Z51 Corvette |
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04-01-2007, 02:27 PM
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cycling has-been
Join Date: Sep 2004
Location: Jersey Shore
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probably a dumb question, but doesn't the effective C/R change when the chambers get boosted?
anyone know an equation? Bill K
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73 911T MFI, 76 912E, 77 Turbo Carrera |
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07-18-2007, 07:28 AM
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Yes, the effective - or dynamic - compression does change under boost. It is not directly proportional to the increase in absolute pressure as the effeciency of the engine will cause a reduction. More air forced through the same size holes (vavles, intake, etc.) will result in less air overall. This is one of my favorite links for approximate calculations;
http://www.turbofast.com.au/javacalc.html
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'77 930 turbo Garretson I/C 1 BAR spring, (2) '82 Triumph Bonneville Royal Wedding Edition Past rides: '74 914 1.9 liter twin plugged track car, '83 928S, '87 924S, '75 911S w '78 ROW 3.0, '72 911T, '70 911T and various other insignificant domestic examples. Happiness is a grey tailpipe! Turbo lag......it's worth the wait! |
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07-19-2007, 11:54 AM
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cycling has-been
Join Date: Sep 2004
Location: Jersey Shore
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thanks, pretty cool link.
I estimated VE at 70% and the numbers came very close to what I was expecting for the 3.0 L. Is the Volumetric Efficiency estimate black magic? Bill K
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73 911T MFI, 76 912E, 77 Turbo Carrera |
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07-19-2007, 12:42 PM
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2002 Porsche 996TT
