Unleaded Conversion 2 ?

["Peter Voorhorst" <peevee@open.net>]

I went to a Morgan specialist to ask his advice about unleaded conversion
for my Kent engine.
He told me: " Using unleaded fuel RON 95 requires a different ignition
timing,   3  instead
8 degrees B.T.D.C.  This will reduce the performance of your engine by 10
to 20 % ".
Is he right ? 
Who has experience ?

Peter Voorhorst
The Netherlands
4/4-2str. 1979
peevee@open.net