In a message dated 5/25/2012 12:42:43 A.M. Eastern Daylight Time,
echristley@att.net writes:
I'm
showing a MAP of around 55kPa, about half of sea level static, with an idle of
1400 and an AFR of 18:1.
I'd like to drop the idle further. I had
it closer to 900 before, but the idle is now rather rough, which I'm
attributing to the ultra lean mixture. Is this the lowest MAP I can
reasonably expect? Or is there a reasonable expectation of a manifold
leak?
A garden hose on the suspect manifold junctions will show up a leak, as the
engine runs better with water blocking part of that leak. But don't panic yet.
Observations seem to be normal so far. In closed throttle situations where
little air is available you see timing have a new power over performance. Lean
mixtures burn very slowly and you may find happiness with more advance just at
idle. Over-lean idle tends to hunt a bit more than a rich idle. Also the load
from the prop drops off rapidly with RPM.
The RX-8 maps up to 44 degrees on high RPM closed throttle, like going down
hill, or slowing from speed.
Get some idle RPM data from another user. There is a too slow number to be
avoided. While the rotary does not have reversals like a piston engine it does
have two major torque pulses per revolution.
With little flywheel effect and low RPM it can shake the daylights out of a
gear box. The racer has only a 5 1/4" Tilton button clutch bolted on over a
flex plate. If the idle is too slow it shakes the transmission so hard you can
hear it a block away. The late Mr. Graham stripped off the teeth in his gear
box, fortunately on the ground. Notice that Mazda
rotaries have flywheels that look like Caterpillar diesel
pieces.
The racer idles at 2,200 RPM. Minimum useful RPM is about 7,800.
Had a bit of a flood here a few weeks back. Had to run back from Florida
early. Racer is OK. The spare engine was on 4X4 blocks on the floor and now
needs a rebuild to check for water (and mud) damage.
Lynn E. Hanover
BTW, Lynn, now that I have a fairly stable idle, I'm
looking closer at the timing. It looks as if the RPM jumps from 1450 to
1250 as the timing drops from 21 to 20. There are many places in the
graph where I can watch the RPM following the ADV up and down, which tells me
that I still have a lot of power left hiding in the timing tables. (The RPM
rises when the timing does.)
I also made a point of noting the EGT
gauge reading. I stayed down around 1200*, for the most part, but did
have an excursion up to 1600* with the throttle 70% open. The MAP read
93kPa. The AFR was swinging between 15 and 14.5. I've since
shifted the numbers to avoid doing that, but it will have to wait to get
tested. Had surgery to repair a torn meniscus on my knee
today.
--
Homepage: http://www.flyrotary.com/
Archive and
UnSub:
http://mail.lancaironline.net:81/lists/flyrotary/List.html