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Registered
Join Date: Jan 2005
Location: Los Angeles CA
Posts: 323
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911 2.2 to 2.4 E or S pistons?
I was looking in the rebuil book deciding on my new engine configuration. I luckily have access to both a set of E and S 2.2 P/C's and was considering stroking with the 2.4/2.7 crank.
In Wayne's book he recommends using both of these setups but states that the E pistons /2.4 crank give a Comp. Ratio of 10.1 and the S pistons give a CR of 9.8. Can this be right? I would prefer to use the S pistons as I already have them where I would have to buy the E ones. Also is there a rod difference?
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1971 911E 2.7RS interpretation -- Signal Orange baby! |
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Re: 911 2.2 to 2.4 E or S pistons?
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John '69 911E "It's a poor craftsman who blames their tools" -- Unknown "Any suspension -- no matter how poorly designed -- can be made to work reasonably well if you just stop it from moving." -- Colin Chapman |
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Registered
Join Date: Jan 2005
Location: Los Angeles CA
Posts: 323
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I can get good pump gas (los angeles area) I don't really want to twin plug. That's why i was leaning to the lower CR. I was just surprised that the book stated that the S pistons would give a lower CR than the E pistions. I will customize the cam grind to the motor, again not sure here, probably an E or S grind.
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1971 911E 2.7RS interpretation -- Signal Orange baby! |
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Join Date: Mar 2003
Location: napier, new zealand
Posts: 33
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Even after you search on this topic it still remains a little confusing as to whether 2.2S pistons with a 2.4 crank is o.k. on todays gas without plugging etc.
There are some very knowledgable people on here that hopefully will chime in???? i read here somehere that the CR in porsche engines was generally overstated - so the actual CR of 2.2s pistons in a 2.4 is below what it should calculate out to if the original 2.2 CR was as stated... 2.2E pistons will have a lower CR in either application. Plenty of people have done this upgrade on 2.4's on this board and i have not seen a warning of it yet. I think you have to be careful if you a re building up a motor from different years that may have been machined etc that could bump up the compresson further. I am replying on this hoping i am right.... I have 1000miles on this rebuild - 2.2s pistons 2.4crank 69E cams 2.2 T heads. single plug using 96 RON to be safe - my mechanic had done this mod before - no problems reported by other owners. awesome motor but i have no real comparison to offer re different cams etc. hoping its going to last..... nathan |
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Warren Hall Student
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Although there seems to be a bit of confusion over what the actual compression ratio is. Rest assured that the 2.2 E pistons will give a lower CR than the 2.2 S pistons when used with the 2.4 crank.
If you already have the 2.2S pistons then I would keep them. You can always lower the CR with shims under the cylinders if you need to.
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Bobby _____In memoriam_____ Warren Hall 1950 - 2008 _____"Early_S_Man"_____ |
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