hi compressions: wasDIY_EFI Digest V1 #258

[Dirk Wright]

On Tue, 3 Sep 1996, RD Rick wrote:
> 
> I have read that the big reason for four valves is to get the spark 
> right in the center.  
> That's as I understand it.  Comments?


According to Mr. Mackerle, of "Air Cooled Motor Engines:" 

	"More advantages are offered by the use of a hemispherical
combustion chamber with inclined valves. The exhaist valve of such a
layout can be efficiently cooled on the whole of its circumference. The
maximum flow area is about 32% at the inlet valve and 22.3% at the exhaust
valve. Small changes can still be made by altering the respective sizes of
the valves and by construction details. The conditions prevailing with
aluminum alloy heads, in which inserted valve seats are used of necessity,
are probably less favorable. 
	"By the use of a "pent roof" four-valve cylinder head layout, the 
flow area at the exhaust valve seats may also be increased to about 32% 
of the piston crown area. The coefficient of flow through the ports is 
however less favorable than in the forgoing case (hemispherical 
combustion chamber), for flow is restricted by the close proximity of two 
valves and on the outer side also by the vertical wall."

Hope this helps

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Dirk Wright 					            wright at uspto.gov
"I speak for myself and not my employer."               1974 Porsche 914 2.0
"A real hifi glows in the dark and has horns."            1965 Goodman House
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