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(Bob) wrote in message ...
My Volvo AQ130C 4 cyl/130 hp engine (a factory rebuild with about 85
hours on it now) pings when I am at sea level and running above about
4400 rpm...not a real bad ping but a ping none the less that concerns
me...this despite using 91 octane gas with octane booster added to it.
It does not ping at all at on Lake Tahoe (6200') using the same
gas/octane booster. I checked the ignition timing today while out for
a cruise on Lake Tahoe and it was right on spec, which does not
surprise me since the engine was installed and tuned at Lake Tahoe.

My question is this...does altitude affect ignition timing? I guess
one way to find out is to put the timing light on it next time I have
it down at sea level.

Any other ideas why it might ping at sea level?

Is this a carburated or fuel-injected engine? If the engine was
"tuned" to run at 6200', the mixture may be set too lean for use at
sea level.

But yes, timing too far advanced can cause detonation too. And you
can get away with advanced timing at altitude if the mixture is too
rich.