Just found it interesting that's all.
While playing with the degree wheel and ports I was wondering what exactly
happens in the inlet manifold when the apex seal goes over the ports - as you
say their open 24-7.
I was all over the shop before, but now I think
I've got it all sorted. I was trying to see the differences the PP gave in
overlap and open ( intake) time.
I was confusing myself yet again, until I
realized I was looking at the degrees of crank, when I should have
been looking at the degrees of the rotor.
With IO @ 32 degrees ATDC
and IC @ 40 degrees ABDC (12A
engine)
or IC @ 310 degrees ATDC = 278 degrees/3 = 93
degrees of the rotor
I did the same for Exhaust = 415 degrees/3 =131
degrees.
Overlap ( standard) =25 degrees/3 =
8 degrees.
Overlap PP = 144 degrees/3 = 48
degrees.
PP inlet = 430/3 =143 degrees.
Inlet time with the PP is an additional 50
degrees (very good) but with a penalty of 40 extra degrees of overlap (bad)
but only bad at low RPM's.
Interestingly the overlap is 6 times the
original - this all varies accordingly with the different
models.
While doing this exercise it is interesting to
see the RX 8 port and why it's placed where it is to eliminate overlap.
While it might be nice to have say 180 degree of rotor ( or more) for
complete burn of the fuel, realistically the power derived from this
exercise would be marginal at best. The power from combustion would (I
believe) be totally converted to mechanical power ( to the rotor) by
the time it reaches the existing exhaust opening.
George ( down
under)
It is endlessly interesting to turn this thing around slowly and watch
the ports open and close. The published open and close events from (for
example) Paul Yaw's web page
WWW.yawpower.com are at the crank.
So being so many (crankshaft degrees) ATDC or BTDC is looking at a very
small portion of a cycle that requires 1080 degrees (3 complete revolutions)
of crankshaft rotation to complete. One of the many advantages of this
engine is that everything is happening in slow motion. In regard to most
engine functions this is good news. Sadly this exposes way too much iron and
aluminum to the combustion process in each cycle. So you get quenched out
flame fronts and unburned hydrocarbons, (HC) and a bit less efficiency
compared to a piston engine of the same displacement. It has no squish areas
to drive mixture to the flame front or spark plugs. In the Fiat I could run
.040" clearance between the head and the piston top and move all of the
mixture into the plug and flame ball. So long as the piston didn't touch the
head too hard at TDC all was well, and it would run with 14:1 compression
ratio.
Of the two tube frame cars, the first gen with the factory Pport engine
was far easier to drive around in the paddock at below idle speed in first
gear. It was not required to declutch and add revs now and again to keep it
moving. The exhaust dilution was very bad and this gives you a very slow burn,
and a nice long push in each cycle. It was just like a stock car. Very
tractable. The third gen car has a bridge port that opens at 110 degrees BTDC
and the overlap is way more than the Pport. It is just about not drivable
without declutching and adding revs to 4,000, then letting in some clutch
(grabby 2 disc metallic) for a lunge, then repeat. Very hard on the clutch.
Engine stalls about 20 times on the way to the false grid and so on. So we tow
it there with a little tractor.
The Pport is very friendly. It is soft in power output until it steps up
on the tune at about 5,500 RPM, where the exhaust port closes soon
enough to keep a good amount of mixture in the engine. While the porting
numbers suggest that the intake port is closing at thus and so degrees, it
never actually closes does it?
Where the side port gets the flat side of the rotor actually sealing it
off, the Pport gets the point of a rotor passing through, valving mixture up
or down but never closing the port. Never closed is a lot of intake
time.
No matter how badly you design your inlet tract, the Pport will provide
outstanding power. Should do well from 3,000 RPM to about 14,000 RPM.
The Pport intake is open for business 24-7. That is where the power comes
from.
While the gearing allows the rotor to turn (rotate) one time for three
rotations of the crank, the stress on the crank is monumental. At 10,000 RPM
the full centrifugal loads of two 9 pound rotors are on the crank and rotor
bearings. It happens that the bearing area is well up to the job. Much
confusion results from the gearing and speeds involved.
The engine is far over-square. And the poor torque (from the short lever
arm of the short stroke) is exacerbated by the rotor/crank gearing. So when
you gear the reduction unit at 2.78:1 you have not even got back to one to one
looking at the rotors. But stick with the degree wheel on the crank. Thinking
about the rotor speed will damage your mind. It did mine.
Lynn E. Hanover
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