Paul Yaw wrote:
Paul wrote:
David Carter wrote:
Paul Yaw and Tracy Crook,
Good exchange of info and perspectives - as usual.
Looks like you are pretty much in agreement about what the two respective
items of equipment do, you both have hard data, but there has yet to be
direct dyno or "in-flight" comparison.
I normally print and file all this stuff and analyze it off -line but this
one is pretty important. Based on what PY said about MSD, I pretty much
decided last week I wanted the improved fuel burning efficiency (lower BFSC)
and maybe a bit more power and was willing to pay the dollar and weight
penalty. Was just going to "lurk" here a few more weeks then e-mail Tracy
and ask if his system could interface in any way with the MSD things, even
though I already have a feeling that they will not be compatible and that
I'd have to install the MSD system as one separate independent ignition
system and use Tracy's system as a separate system - which would then give a
a TRIPLE re?dundant ignition system. Using two separate systems that both
fire all 4 plugs would require use of the MSD brand "Y" or "T" connector on
top of each plug to allow each plug to be attached to both separate systems.
Tracy's system uses the stock Mazda trigger device. Assume I'd have to
install a Hall effect device on flywheel to trigger the MSD system.
However, Tracy's response, and PY's response to Tracy's response, seems to
show that the Stock Mazda coils are about as good as you can expect and in
fact the MSD's might not provide that much improvement.
Here's my questions: 1) Does the MSD system provide longer spark duration
and better burn than Tracy's system using the acknowledged efficient stock
Mazda coils? 2) Could Tracy's system be modified to provide longer
duration sparks to emulate the MSD capability?
I think there is some confusion here. The MSD is a capacitive discharge
unit which is used to fire the coils. You can use any coils with it. I
would suggest the stock coils. My own testing has shown that coil
selection is not that important if you are running an MSD, but if you
are using an inductive discharge system it is very important.
As for duration, I do not know which is better, but the MSD certainly
delivers more spark energy. I personally do not think that duration
matters a great deal at high rpm, but I may be wrong about that. I am
considering 6000 to be high rpm. The arrangement that you described
above seems quite complicated. If I was going to do this I would use
Tracy's system to Trigger the MSD. The problem is that now you have
added more pieces that can fail. If you want to experiment with this,
you need to talk it over with Tarcy to make sure that there are no
compatibility problems. To make things even more confusing, the MSD
seems pretty picky about how it is triggered. It works great if you use
a magnetic pickup, but if you try to run it from the stock '81-85
ignitors it doesn't work much better than the stock system. If you call
MSD and ask about this, they will say that you are crazy and it should
work just fine. I THINK what it needs is a squarwave if you use the
high level input. That is just my guess. If it can not be easily run
from Tracy's system it might not even be worth doing. You could spend
more time chasing your tail than anything. On race engines we just
build a crank trigger and run it with no advance. I'm not sure how well
that would work in a plane because it makes the idle pretty rough.
I am quite willing to incur the expense and wt penalty to install both the
MSD and Tracy's system and run one at a time for side-by-side comparison.
It will be a year before I am ready to install my 13B engine. I'm just
starting to work on my RV-6 Quick Build kit.
Another question: I couldn't tell which of you commented on the SDS
system - who was it and can you give us a brief evaluation of the system and
how it was used and on what engine?
I used one of their four cylinder fuel and igniton systems adapted for
the rotary. I used it for several reasons. Over boost control, Over
rev control, complete timing control based on manifold pressure, manual
mixture adjustment, knock sensor with programmable retard, and they have
a couple dozen in the air already.
If SDS is using crummy GM components,
have they been given feedback to suggest using different components to
improve performance? I am interested because they seem to have a really
good system and it is used in racing, both 13B rotaries and piston engines.
The GM coils are normally used in a wasted spark arrangement (On a
piston engine) Each coil fires two spark plugs at the same time. These
coils, I found out later, fire the plugs in series! It is not so bad in
a wasted spark arrangement because one of the plugs will normally be
firing under low pressure. Using it like I did in the rotary to fire
leading and trailing at the same time, both plugs are under pressure so
it is not easy to fire both of them. I ended up with a .025" plug
gap. Since the plugs fire in series, the polarity is wrong on one
plug. So, their system works OK on a piston engine, and it actually
worked OK for me too, but it certainly could have been better. Some
piston engines are not at all picky about how you fire the plugs. They
can configure the system to trigger an MSD with any coils that you wish
to use, and that is a popular option on turbocharged engines. They
don't actually have a rotary fuel AND ignition setup, I just talked them
into adapting this one.
This is getting long, but I need to add one more thing. Ross and Barry
at SDS are great people to deal with. They are very helpful, and Ross
is very knowledgeable when it comes to engines. Their product works
just as they say it does. I would not hesitate to use their product
again. I would however do the ignition system differently. If I do a
naturally aspirated engine for an aircraft I would like to use Tracy's
system. For the turbo application I needed the extra control that the
SDS unit had.
PY
The Aircraft Rotary Engine Newsletter. Powered by Linux.
http://home.earthlink.net/~rotaryeng/ http://www.linux.org