Bullwinkle,
One thing that everybody is forgetting is that most MG engines
are
small bore, long stroked engines. This automaticly gives more
complete combustion as the flame front does not have to travel as
far
in the time available. This provides a two fold benefit: 1)
lower
octane fuel may be used for a given compression ratio, 2) lower
emissions. Other side benefits are: lower inertial stresses
imposed
on the rods and pistons and less thermal loss to the head and
cylinder
walls due to less surface area rusulting in higher thermal
efficiency.
The bad side: long rods are more prone to brakage at high rpms,
lower
crankshaft strength, taller engine, greater ring wear (though
somewhat
offset by better modern oils), greater pumping losses due to
small
valve area.
Power is directly related to how much air is pumped by the
engine.
Since long stroke engines can't turn real high rpms, less air is
moved
and less power is developed.
After running is most often the result of hot spots in the
combustion
chamber. Getting rid of sharp edges, particually around the plug
hole
where the metal is quite thin at the face of the combustion
chamber.
This is more of a problem on engines that have had the
compression
raised buy milling the head. By removing the hot spots and by
using
the correct heat range of plug to keep fouling at a minimum under
your
normal driving conditions then carbon build up will be kept down.
Keeping the operating temp high will help promote more complete
combustion and less deposits from forming, thus reducing the
chance of
hot spots caused by "coke". Indexing the spark plugs will also
help
in keeping after running to a minimum, though this is most often
done
to help clear burned fuel from around the plug points to promote
better ignition of the fuel air mixture.
It is a balancing act of getting the right fuel mixture, plug
heat
range, fuel octane, combustion chamber design, ignition timing,
valve
settings (and timing), coolant thermostat temperature, etc. to
get a
smooth, efficient, and well mannered engine.
zandor
|