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re: compression ratio - there’s no magical line where 9.8:1 is fine and 10:1 is dangerous in a single plug application. Further, you’re only looking at static compression: it’s dynamic compression ratio (DCR) that has the most impact on detonation.
You can lower DCR by running a more aggressive cam: the 964 grind is mild vs. a 993SS grind from Dougherty or WebCam. With a 964-grind cam on a 3.2, your DCR is closer to 8.37:1 - with a 993SS grind, closer to 8.14:1.
You can also manage ignition timing here. Lots of variables to play with.
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1978 911 SC (3.2SS, EFI, 993SS cams + the trimmings)
Dynamic CR calculator: https://dcr.questionable.services/
Last edited by silverlock; 04-08-2025 at 09:58 PM..
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