The atmospheric valve does work ...but not if you want revs and power, as HD concluded nearly 110 years ago.
Diameter is one factor. The force available to open it = the valve area X the differential pressure (atmos to inside cyl)
Counteracting that force is the mass of the valve X the acceleration required to open it in the time available + any spring, if fitted.
In my calculations for the Supercharged (reverse) uni flow in Oddball I was looking at basic 28mm Titanium 4 stroke valves.
Force available with 0.5 atmos Boost (and 0 abs. in cylinder) was around 9.25kg
At 2500 rpm you have 0.006 sec to full open the valve from say 90 atdc to bdc.
For 7mm valve lift, the acceleration required is 388 m/s2.
Maximum permissible weight of a valve at 2500 rpm was around 24g, which is almost realistic.
Unfortunately, the acceleration increases by the inverse of the available time squared.
At 5000 rpm valve mass must be 6g. At 10,000 rpm = 1.5g.
Sufficient lift to achieve a decent Intake/scavenge STA plus the rpm limits are a problem.
Hence Frit's suggestion to make a Christmas wish for
Fireproof, pressure-proof, detonation-proof reeds that open at the slightest pressure differential, and with so little mass that they'll allow any rpm...
The other problem I have with a piston crown valve is that we still have a 'petroil' bottom end and are not eliminating a significant source of HC emissions.
On the other end...a super/turbocharged reverse uni-flow with a single, do-nut shaped CCC valve in the head
Real foundry stuff is also coming...
Cheers anyway! Daryl.
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