Norm
See my earlier e-mail on the NGK plugs. The David Vizard book "Tuning the A
Series Engine- the definitve manual on tuning for performance or economy"
(the "bible" for the A series engine builder) says that the plugs are 3/4"
reach.
The listed plugs tend to be the extended, or projected, tip plugs as these
are said to protrude into the combustion chamber for better cooling and more
power.
By heat ranges from coldest to hottest:
NGK BP8ES, CHAMPION N-7Y, N-6Y, Bosch W260T30
NGK BP7ES, CHAMPION N-9Y, N-8Y, Bosch W230T30
NGK BP6ES, CHAMPION N-10Y, Bosch W175T30, W200T30
Vizard suggests that race A series engines use the BP7ES or BP8ES, although
he says that it is worth trying out the retracted nose plugs, which is what I
use. He says that for no obvious reason some engines seem to respond better
with the retracted nose plugs. He says that the only drawback is that
starting from cold sometimes may be a problem, but that has not been a
problem in my experience.
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