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Registered
Join Date: Nov 2004
Location: Redmond, WA
Posts: 98
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CR of a '70 911T?
The tech specs say a '70 911T has a CR of 9.1:1, but after adding a 2.4 crank I measure it to be 8.27:1.
I just came across some random web page that listed the '71 T as 7.5:1, which would make more sense. I quadruple checked all the measurements. The pistons are so flat that even with a deck height of 0 the CR only goes to 9.3. Everything is stock except for the crank, so I'd expect the CR to be a bit higher than from the factory. Is the 9.1 value wrong? Jeff |
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03-15-2005, 03:30 PM
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Registered
Join Date: Jan 2002
Location: VA
Posts: 591
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8.6 is what my Porsche 911 Red Book says. Es had 9.1, Ss 9.9.
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03-15-2005, 05:05 PM
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Registered
Join Date: Nov 2004
Location: Redmond, WA
Posts: 98
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Ok, that's closer. I still don't get how a longer crank lowered the CR
 Could you check what the stock deck height was? |
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03-15-2005, 05:53 PM
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PRO Motorsports
Join Date: Nov 2001
Location: Burbank, CA
Posts: 4,580
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A 2.2T is 8.6/1
A 2.4T is 7.5/1 Theoretically, you should end up with 9.15/1 when you put that carnk in your engine. But Porsche has apparently over-stated their compression ratios. Pretty much every engine is at least a half point lower than advertised CR.
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'69 911E coupe' RSR clone-in-progress (retired 911-Spec racer) '72 911T Targa MFI 2.4E spec(Formerly "Scruffy") 2004 GT3 |
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03-15-2005, 06:47 PM
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Registered
Join Date: Nov 2004
Location: Redmond, WA
Posts: 98
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Thanks, that's really helpful.
Right now my deck height is .050", and the CR is 8.27. Reducing the deck height or cutting the heads will increase that. Think the increase in CR is worth it? Jeff |
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03-15-2005, 07:04 PM
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