You may have the start of a head gasket leak causing coolant
to enter a cylinder under high-load conditions. As soon as the exhaust
and catalytic converter get very hot, the water may vaporize completely
and stop showing up as white smoke. The coolant (ethylene glycol) will
solidify and form deposits on front of the catalyst, eventually causing
it to overheat and melt down. Have it tested for the head gasket leak
first.
—Jim O'Neill
Chino Autotech Inc.