as I understand it, Range 4 and above over-revs are grounds for voiding warranty coverage by PCNA (CPO or OEM). Yes, I understand it's only 1 ignition (a seriously quick catch on an almost serious $-shift) but it is in the range and all the way up to 6
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At the very least, you'll want a signed letter on the dealers stationery stating these over-revs occured prior to CPO certification. IMNSHO though, there are too many 986s and 987s out there which in all likely-hood do not have over-revs to risk picking one up that has them. Good luck in your search.