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It makes no sense for a 2.2L engine to be at 35deg ign while the sister 3.0L engine is at 25deg. For some reason the factory detuned the 3.0 and 3.2 engines.
Sal,
The reason is history. After the oil embargo, Porsche decided that advertising lower fuel consumption numbers for each new model would be very important to maintaining image and sales. They decided that increasing compression was the way to go in 1980 and 1984, but with the unleaded fuel mandate, this required detuning the ignition advance. The later SC fuel spec is 87 CLC octane.
The later 3.0 and 3.2 are very different engines in terms of knock sensitivity. The SC has much smaller ports and runners that boost the low rpm torque peak. Unfortunately with a distributor it is very hard to reduce the advance around this point. An SC that runs hot will ping like crazy at 4000 rpm with 30 BTDC timing. One of the the best things you can do with a stock SC is get the hot breather oil out of the intake. The higher temps and oil dilution raises the engine's octane requirement.
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Paul
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