Al, I did not catch what your
ignition timing you have set when encountering this. IF you set the
ignition timing with little/no advance/retard then you are around 25 deg BTDC.
ED;
The static timing is set according to Tracy’s spec; 35o
BTDC with 2-point trigger aligned. From there it’s up to the EC2
built-in timing curve.
IF you ignition was advancing to the
point that the leading plug spark point was exceeding the optimum for those
combustion conditions (rpm, manifold pressure, ignition timing, etc),
then the trailing spark which lags might start to become the optimum
spark in relation to the optimum spark point. If so then I would expect
the higher the rpm the more influence the trailing spark might have.
Thank you for that. We had experienced
this on the dyno; but my recollection has been backwards. I have been thinking
that it indicated the timing was late. You forced me to go back and check my dyno
report; which says:
2.) Engine ran better
on trailing plugs than on the leading plugs. After much double checking,
head scratching, and some further testing we concluded that the only
explanation could be that the timing was actually very much early. And
the only way that could be true was if the timing marks and the pointer did not
relate to the position of the rotors.
By viewing the
position of the apex seal through the two spark plug holes, measuring angles,
etc. we made a new TDC mark on the pulley, and a new 20 Degree BTDC mark.
Then reset the static timing on the crank angle sensor, and fired up. Ran
well, and disabling leading had a bigger effect than disabling trailing, as one
would expect. To verify timing we put a pressure transducer into the
trailing plug hole, ran an oscilloscope trace triggered by an inductor on the
leading plug wire. One step back on the EC2 timing adjustment gave us the trace
we wanted. (Fortunately, operators knew what the right trace looks like based
on their prior rotary development work). The original timing mark was about 15
degrees too early – apparently the result of using a 12A front cover
(with pointer) on a 20B; using the stock 20B pulley.
So; now I believe the
timing is too early at the higher power. But the question remains – why?
And is it curious that it seems right at low power, and too early at high
power? In any case, I will retard the spark and see what that does.
2.
Unlikely
as well, but I assume there is no change the coils (you have six?) could be
sequenced/hooked up improperly. I don't know what the effect would be if
the leading coils were sparking the trailing plugs with the EC2. I know
the timing split between the leading and trailing is much less than in the
automobile ignition timing - but I do not believe it is zero. So the
engine might well run, but might have some unexpected things happening.
Worth another check. My understanding
from Tracy is that leading and trailing fire at the same time – unless it
has changed since we talked about it.
3.
I
have disabled my leading ignition while flying (it helps if you encounter
a bad case of SAG) and I notice no difference in power although the EGT on both
will increase about 150F from 1600-1750F. Do you notice any change in
your EGT when you do this?
That’s interesting – I would
expect that you would/should. Have you tried disabling the trailing?
Al
----- Original Message -----
Sent: Tuesday,
September 18, 2007 3:40 PM
Subject: [FlyRotary]
Re: One for the guys that don't give up
The reason Tracy gave for
the ECU not working was because of that set-up, as his Vacuum pick -up
is at the Plenum - something to do with fluctuations within the tube,
whereby the plenum was static or less successful to wild fluctuations.
George ( down under)
I
have accumulator and orifice which smooths the MAP nicely.
Dave said: Besides a slight difference in the
mixture necessary between the 2 computers, both locations seem to work well.
Dave:
Mine works well also - except for the anomaly noted. I don’t know
if you mean that yours specifically doesn’t exhibit that phenomenon?
Al, was
35° BTDC Tracys suggested timing?
The
35o BTDC is the static setting specified in Tracy’s manual; line
up the 2-point trigger wheel with the reluctors at that point.
Quite frankly, I haven't tried the coil disable
feature at high rpm yet. So, I don't have an answer to your
question. Heck, I can't even get my auto-tune to work.
Mark;
well, whenever you get that far, give it a shot and see what you get. Good luck
with the auto-tune.
Does anyone else experience these symptoms?
That’s the
question.
Thanks,
guys,
Al
OK; Mark; (or anybody). Since we both have 20Bs, and both use
the EC2 controller, maybe you have a clue for this one. I’ve brought this
up here before, but no solution.
I
have all the latest updates on the EC2, and I have double checked the static
timing set at 35o BTDC. From that point on the EC2 is handling
the timing curve with rpm and MAP.
At
lower power levels, disabling the leading ignition clearly has a larger effect
than disabling the trailing – as one would expect. At somewhere
around 18” MAP, (don’t know right now what rpm that is, maybe close
to 4000) the effect is about equal when disabling either set. At higher
power levels, there is a larger effect of disabling the trailing than the
leading. That troubles me. I think the leading should always have a
greater effect. It makes me wonder about the timing; or if something else
is wrong.
I
have in the past tried varying the timing 2 or 3 steps while at power, but
couldn’t discern a change in rpm greater than the normal variation in the
readout. Tracy sent me the XL spreadsheet with the timing curve data, but I
haven’t yet figured a safe way of checking it with that prop spinning
close by.
Does
your installation exhibit the same behavior? Is there some explanation
for this? What test should I perform?
One
thing that occurs to me is that Tracy measures MAP out before the runners. I measure MAP at the
manifold, downstream from intake plenum and three short runners and the
3-barrel TWM throttle body. At WOT my MAP is not atmospheric pressure
– it is maybe 2-3” HG less. I can’t quite see how that
is an issue; but maybe someone else with a TWM TB setup with the MAP port
downstream would know.
Other
than that I’m very pleased with the new mixture correction table setup
for the 20B. Much less tuning and seamless transistion between tables and
through the stage point. Probably the pulse clamping and injector
isolation diodes are part of that.
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