Hemi Heads

[Keith Walker <100662.3423@domain.elided>]

>>Hemi heads are not about good breathing per se, but about valve area.
Hemi
head allows the biggest valves to fit when only two are used. Bigger valves

breathe better than smaller ones, duh. However, with multiple valves you
can get better breathing without going hemi shape. When you dial in big
bores and high compression you get multiple valve engines with pent roof
heads.<<

As I understand it a hemi head has no real advanatage over a pent
roof combustion for valve area. The big advantage of the hemi head
is the combustion chamber shape which is very good. However it
just doesnt work with 4 valve heads unless you have them laid
out radially around the head which becomes a manufacturing
nightmare. The only people I can think of who have radial valve
heads are Honda and Aprilia and both of those are on single
cylinder engines with twin cams

All the best

Keith
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