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Al, let me clarify my comment about the split
timing. In the automobile the trailing plug is electronically set to
"trail" the leading by approx 15 deg (as best I recall). I believe the
physical location of the trailing plug offsets the timing something like 5
deg, so even if the sparks happen simultaneously from the EC2 , the trailing
plug is still further behind in the rotation combustion timing
progression. Now, whether this would have the effect you are seeing, I
certainly don't know.
I would certainly check and make certain they didn't send
you home with the incorrect pulley (just kidding).
Perhaps while the engine appears to be running OK at the
lower rpm, it might be that the effect is not as adverse because leading plug is
still within an acceptable sparking region - but as rpm gets higher and more
advanced is needed/signaled it advances out of the optimum zone and the trailing
plug moves into it. In otherwords, correcting the problem might give you
even more power at lower rpm.
Yes, I probably did disable the trailing when I was
experimenting trying to less the SAG effect, but once I found that disabling the
leading apparently help raise the temps and burned off some of the carbon
temporarily eliminating the SAG effect, I just didn't try eliminating the
trailing spark any more.
I personally would double check (without the timing mark)
your static timing mark using one of the many techniques to establish Top Dead
Center by viewing the apex seal, etc, and verify that the mark you have
on the cover and/or the pulley is indeed TDC.
Good Luck
Ed
----- Original Message -----
Sent: Wednesday, September 19, 2007 12:00
PM
Subject: [FlyRotary] Re: Strange
Ignition?
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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