Bill:
Dave has mentioned the higher HP available via higher RPM-- which is allowed
by the lighter valves/ less inertia/ less tendency to float. Quite true,
and quite a sizable advantage.
There is also more HP available in a multi-valve due to better breathing.
Consider a 3.5" bore; assume you have room for the spark plug, an exhaust
valve, and--say, a 1.7" dia intake valve. At .1" lift, the flow window
"cylinder" (between the lip of the intake valve and head) is 1.7pi X 0.1=
0.53sq.in.
In that same space, you could easily put 2ea. 1.4" diameter valves. Again,
looking at 0.1" lift, 2 X 1.4pi X 0.1 = 0.88sq.in. As you can see, a
4-valve engine can easily achieve a 60% improvement in breathing. Run the
numbers and you'll see that this holds-up throughout the range of lift (it's
a linear equation).
Russ, #1226B
-----Original Message-----
From: owner-land-speed@autox.team.net
[mailto:owner-land-speed@autox.team.net]On Behalf Of ardunbill@webtv.net
Sent: Wednesday, February 26, 2003 2:05 PM
To: land-speed@autox.team.net
Subject: Four-Valve Pentroof Chamber VS Two-Valve Hemi Ditto
One of my West Coast Vincent friends,
Bill Martz, who enjoys the Ardun and LSR items I send him from our List,
wanted to pose a question to the technical experts here. Bill was half
of the Martz-Auger team that was famous in Southern California for years
in the '50s, campaigning a 90% nitro Vincent Black Lightning mc on the
dragstrips. He was the technical side, and his pal Tommy Auger was the
fearless lightweight rider. Some of you with white hair like me may
remember them from Hot Rod in that era. They sometimes got the ink.
Bill's question is, what are the advantages of the four-valve head of
today compared with the traditional two-valve hemi head design(still
very much with us)? Thanks, Ardun Bill
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