An Engineering Query

Sir,

I am interested in the comment contained its Mr Stapley's letter regarding the burnt exhaust valves On his Hunter. I am under the impression that the only damage likely to occur through the use of high octane fuel in an engine not designed for it, is to theowner's bank balance!

Is it fact that one can actually do harm to an engine by using a higher octane fuel than the designer intended or is this the start of another "overfilled sump saga"?

Ashford. A. SHAPLAND