So.....since the rotors weigh the same within measurement error, the
ability to rev to the 9,000s range vs. 7,000s range is not related to the
orbiting mass of the rotor. (Note: the motion is NOT truly circular, it
is an epicycloid path that the center of mass of the rotor takes. That
10 lb. rotor flops around plenty (technical term) and 10 lb. is lots heavier
than an aluminum piston!
It is apparent from an article on the "other" site, that the wall
thicknesses and casting detail are lots more refined on the RX8
rotors than on earlier models...for more uniform and desirable heat
transfer and uniformity.....oil cooling the rotor, etc.
The mass being basically the same, it becomes a high probability that
since centripetal force is F = (Mass x rotational velocity
squared)/radius of rotation, {F=(m x w^2)/r}, it must be the weight
of the seals themselves that are the critical
element? The force at 8,500 vx. 6,500 is (8.5/6.5) squared or 1.71 times
greater. Might this be why seal wear on the original seals goes up
substantially at around 6,500 rpm?
Tell me....why would one increase the depth of the seal groove of an RX8
rotor to allow a heavier seal???? On the RX8, 3.25mm/9.5mm =>
approx. 34% reduction in apex seal mass!! A lighter seal means
a whole lot less force of the seal against the housing at 8,500 rpm!!
Anyone want to go back to old seals and rev to 8,500 rpm?
Note: the seal force against the housing at 8,500 rpm on the RX8 is
still higher than the old seal at 6,500.... (.66 x 1.71 = 1.129). Not
much more, but there are probably even more very small details that we
are not at first glance able to know and understand? Seal
material/housing material compatability is probably one significant
factor?? (I used 9,000 vs. 7,000 and the numbers still come out about
10% higher seal force on the RX8, even with the lighter seals.)
Having been an R&D engineer at FoMoCo, it is hard to explain to most
persons the creativity, detail, imagination, trial and testing and testing and
testing and testing and ...... which goes into making an engine
acceptable for production in quantities of XXX,XXX's and higher. (One
simply can't be wrong...it could bankrupt even the largest OEM.)
And....those Mazda engineers have done what many OEM's gave up on many years
ago. How? Through their persistence and incredible insight into
the issues.
Before one gets the wire EDM out and starts going counter to what Mazda
no doubt spent many $$$$ (more than all of our annual incomes put
together??) on how to increase HP in an RX8, more information is needed before
we start mixing and matching just because the parts will fit. I
know we are experimenters here, but lives of some who may not understand the
"physics" limitations will ultimately be at stake.
Above all: Just because something works for 100 miles in a sprint
race DOES NOT mean it will work while hummmming along
for 5 hours at a crack at 75-80% max. HP on a cross-country over and over and
over again....hopefully. So far, my Lyc is a piece of 30's era design
and materials...but it has run for 2,000 hours (350,000 miles) at 75-100%
without fail!!
Most of us aren't as lucky as Ed and his "on airport" emergency
landings. Perhaps it is that his green carpet (Carolina's) is lots
more friendly than our granite peaks out here?
Doug in Colorado
Dough,
sorry to disappoint you, but the rotor movement is truly circular. What
makes the rotor housings non circular shape is the "phase wobble of the rpm
difference between the e-shaft and the rotor, and, of curse, the rotor shape.
This is why the rotors are balanced by them selves before they go into the
system.
Richard Sohn
N-2071U