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Thanks Lynn,
It goes without saying that I always appreciate your contribution. I may have to refer back to what you were saying to clarify some points.
I now understand the closing event has the most effect on the mid range power we need in Aviation (why is that? and why is your BP closing of 80 degrees flowing very little - there seems to be plenty of suction still going on?)
The intake closing event is shown as ABDC. After Bottom Dead Center, in the case of the intake cycle is in the top of the rotor housing. (a bit confusing) and since BDC for both intake and exhaust cycles is the largest volume attainable, that closing point is after the volume is already decreasing. So some of the mixture is being forced back into the intake manifold. Early closing means more mixture is trapped in the closing chamber to be used
no matter what the state of tune. So at lower and medium speeds where inertial charging is low to nonexistant, the engine still developes some amount of power. The later the closing point, the more accurate the tune must be to support the same performance down low, as only high inertia can overcome the mixture being pushed out from the closing chamber.
So an early closing point captures more mixture, at lower speeds, and low and medium power is improved. Same as advancing the cam in a piston engine. Even though it screws up the other three timing functions, the early closing intake valve makes so much difference it is worth the work to do it. In a minor way this affects the effective compression ratio as well. More degrees of closed chamber means higher compression. This becomes painfully obvious when measuring compression at cranking speeds. My Fiats had 245 pounds of compression cranking. Run the engine 10 seconds and shut it off because the NOX would fry you eyes. I could retard the intake cam 5 degrees and loose 10 pounds.
and that closing event should not exceed 70 degrees ABDC. This is probably something
you told me previously and I hadn't remembered ( or understood properly). However the Mazda Factory PP is 75 degree IC, perhaps allowing for higher HP at the higher RPM range. Whereas the Leman's engine seems to be about 70 degrees ABDC.
All accurate. The Lemans engine you should point out, was only turned up to about 7,600 RPM. So the early closing point was adequate. Most of the fine work they did was to pump up the mid range so the engine could have a broad power band. The Lemans circuit has a very slow first gear corner, and a 230 MPH straightaway. It is typical when fooling with piston engines to measure degrees of open only after a valve is .050" off its seat. So little flow is available below that point that it is not counted. So your cam card will have lobe centers, total lift, lift minus the valve lash, and timing (measured once the valve is at .050")
(Crane gives you duration at running lash as well).
For timing I Use oil in the port. When the oil begins to flow I mark the port as being open.
There is nothing to record from a dial indicator or similar that I can use to determine this as in the piston engines.
So, the oil works fine. Without the radius the port would open at a bit less than 80 degrees.
So it is not as exotic as it at first sounds.
Secondly, the later the opening event the better ( I understood that one) because of overlap and contamination of the inlet charge at lower RPM. Now if we could just close it before we open it, we would be way ahead - but of course that is not possible, so the squat PP is the next best shape and timing.
So the opening later is better; but the closing later is not good! As we say in Australia - BUGGER!!
Anyhow there is another reference in your response which I don't quite understand and that is "So even with red lines at or above 8,000 RPM this modest port closing is more than adequate (this is understood).
If I remember correctly (this becomes less likely with time) " Can you explain the
last sentence about (less likely with time). Do you mean later openings gave better higher RPM, HP in the racing industry.
Nope. It means I am over 65 now and remembering anything is difficult. LEH
TIA
George (down under)
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