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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.
Here's some thoughts on what might be happening(just a
SWAG). At lower rpm generally require less ignition advance because the
combustion has more time to get completed, therefore the spark does not
need to start as early (less advance). However, as RPM
increases the time for a the combustion event becomes less and less which
means you normally would have your ignition advancing to
compensate. I know you know this, but bear with
me.
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.
So what would you check.
1. I recall back a couple of years ago there was
some discussion about the stock pulleys on certain model year 13Bs being keyed
different (bolt hole pattern) on some year models such that the timing point was
10 deg difference. I don't suppose you have two pulleys laying around that
you could compare the bolt hold pattern in the hub (match two of them up with
the holes and check the timing marks?) and then check hub on you engine. A
very long shot, but thought I would mention it. Because in the
unlikely event you would have a hub mismatch with your pulley then of course,
your timing would be 10 degrees off.
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.
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?
Well, that is about all of the wild theories I can come up
with at the moment.
ED
----- 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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