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Engine detonation

  • 1983
  • 911 SC
90 000
Grosse Pointe Park, 


im building up a nice 83 SC. The engine is stock except for PMO 40s, headers, centrifugal only distributor with a curve that fits within Porsche recommendations for earlier engines. MSD ignition.

I can’t seem to rid it of detonation at low speeds below 3000. I have to feather it in or it sounds like a bucket of bolts. I’m running Sunoco highest octane and have backed starting timing as far as 5ATDC. It makes a difference but still rattles if I get on it even a little.

Any ideas? Are these things really that sensitive to detonation? My timing at the flywheel is 10 at 1500, 20 at 2200, 25 at 2600



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