Blake, If the header is cracked close to the flange and its a good sized crack, that could cause the valve to burn. Relatively cold air getting sucked in there during reversion with unburnt fuel being present, can raise localized EGT and burn a valve. Not sure how yours is tuned but I've seen SM's tweaked to around 13.0:1 AFR's at full load. Not much margin for error there. Not common but certainly possible and I've seen it before on other highly tuned (lean) N/A engines. More common in motorcycle engines.
Cheers, Emilio Cervantes >www.949Racing.com >26242 Dimension Dr #130 >Lake Forest, CA 92630 >949.716.3111 phone / fax
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