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How can I determine the compression ratio?
Motor is in my 78SC. Engine numbers say the case is out of an 85. So I'm unsure whether its a a true 78 configeration with 3.0 and 8.5 to 1. Question is, is there a way to tell the displacement and compression ratio without tearing the motor apart? I'm considering a sc and need to know. Thanks.
------------------ Paul 78SC Targa [This message has been edited by pbs911 (edited 08-21-2001).] |
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08-21-2001, 05:01 PM
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Senior Member
Join Date: Feb 2000
Location: Lacey, WA. USA
Posts: 25,310
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I know of no way to tell what pistons are in an engine without looking inside. But if the engine numbers say it's an '85, I'd guess it IS an '85 engine. Whatever that compression ratio was. I doubt if someone would rebuild an '85 engine to 3.0 specs.
------------------ '83 SC |
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08-21-2001, 09:46 PM
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That's what I was thinking. But does the fact a 85 case was used mean the 3.0 cylinders and pistons were not? Can a 85 motor run on the CIS system?
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08-22-2001, 07:53 AM
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Noah,
All the parts I have replaced, i.e. rotor, cap, CIS composents, etc., have been ordered for a 78 3.0. The only thing that demonstrated its a 85 engine is the engine number. I really don't want to install a sc desined for the 8.5 to 1 compression ratio if I have the compression of a 85. I could attempt to contact the PO. Does anyone know how to such a person down. I bought the car from a dealer so I never met them before. Thanks. ------------------ Paul 78SC Targa |
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08-22-2001, 10:05 AM
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The main difference between the 3 l cis and the 3.2 DME (besides the fuel management,cr etc) was the crankshaft. The 3.2 DME using a 74.4mm throw and the 3 l cis using a 70.4mm throw(there are other differences big end dia. & width wristpin offset etc). They both used the same 95mm bore.
NASCAR uses a sonic device to check cr and cyl vol. since its not likely that one will be available to a mere mortal. Its unlikely that you will be able to dtermine much without disassembling at least 1 cylinder. ------------------ Bill Verburg My Home Page  My Pelican Gallery page My Porsche Owners Gallery Page |
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08-22-2001, 10:24 AM
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Bill,
I actually have a friend that is heavily involved with several of the NASCAR teams and cart teams I think I'll hit him up. Thanks. ------------------ Paul 78SC Targa |
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08-22-2001, 10:43 AM
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1978 Porsche SC Targa 3.6
1976 Porsche Carrera 3.0
1995 Porsche 993 Carrera Coupe
